Automotive Rear Lighting and Signaling Resea~h

HSRI Report No. HuF-5

Automotive Rear Lighting and Signaling Resea~h

Rudolf G. Mortimer

Highway Safety Research Institute University of Michigan Huron Parkway and Baxter Road Ann Arbor, Michigan 481 05

January 14, 1970

Final Report .

July 1, 1968 - December 3 1,1969

Federal Highway Administration Department of Transportation Donohoe Building Washington, D.C. 20591

The contents of t h i s report r e f l e c t the views of the Highway Safety Research I n s t i t u t e which i s responsible fo r the f a c t s and the accuracy of the data presented herein. The contents do not necessar i ly r e f l e c t the o f f i c i a l views or policy of the Department of Transportation. T h i s report does not cons t i tu te a standard, spec i f ica t ion or regulat ion,

1 4. Title and Subtitle

1 . Report No.

J

I Automotive Rear L i g h t i n g and S i g n a l i n g Research

5 . Report Date

Januarv 30, 1970 6. Performing Organizatron Code

1 ,

2. Government Accession No. 3. Reclplent's Catalog No.

I

9. Performing Orpnizatlon Name and Address 1 10. Work Urut No.

7. Author(s)

Rudolf G. Mortimer

Highway S a f e t y Research I n s t i t u t e U n i v e r s i t y of Michigan Huron Parkway and Bax te r Road Ann Arbor, Mich. 48105

8. Performing Organlzatlon Report No. I

HuF-5 !

12. Sponsoring Agency Name and Address

F e d e r a l Highway A d m i n i s t r a t i o n N a t i o n a l Highway S a f e t y Bureau Washington, D .C . 20591

FH-11-6936

F i n a l Report J u l y 1, 1968-Dec. 31, 1969 14. Sponsoring Agency Code

f I

15. Supplementary Notes t- i !

1 16. Abstract 1 A review of p rev ious NHSB v e h i c l e r e a r l i g h t i n g s t u d i e s was c a r r i e d o u t , and a i r e s e a r c h program was planned. Experiments were conducted i n t h e l a b o r a t o r y , by i s i m u l a t i o n , by ou tdoor s t a t i c t e s t s , and i n dynamic s t u d i e s on p u b l i c highways. 1 Experiments concerned w i t h t h e coding of s i g n a l l i g h t s showed t h a t s e p a r a t i o n of '

lamps by f u n c t i o n and c o l o r were e f f e c t i v e t echn iques . I t was recommended t h a t : presence lamps shou ld be g reen-b lue , t u r n lamps amber, and s t o p lamps r e d . An a n a l y t i c a l c a r - f o l l o w i n g s i m u l a t i o n showed t h a t u s e of such a sys tem should reduce rea r -end c o l l i s i o n s . There was a n e g l i g i b l e e f f e c t upon response t o r e a r i s i g n a l s of low d o s e s of a l c o h o l . I t was found t h a t r e a r t u r n s i g n a l s should be '

augmented by forward mounted, amber r e p e a t e r s i g n a l s . Improvements i n d r i v e r s e n s i t i v i t y t o c l o s u r e w i t h a n o t h e r v e h i c l e a t n i g h t were o b t a i n e d i n s i m u l a t i o n and f i e l d s t u d i e s by an a r r a y of f o u r p resence lamps, two mounted h igh and two c o n v e n t i o n a l l y . S i g n a l s shou ld n o t be g iven on each r e l e a s e of t h e a c c e l e r a t o r j n o r can such s i g n a l s r e l i a b l y p r e d i c t subsequen t a p p l i c a t i o n o f t h e b rakes . I

I I n t e n s i t i e s needed f o r s i d e t u r n s i g n a l s , r e a r t u r n and s t o p s i g n a l s were e x p e r i l m e n t a l l y d e r i v e d . Night i n t e n s i t y shou ld be lower than day i n t e n s i t y . An i i n t e n s i t y o v e r r i d e s w i t c h should be provided t o a l l o w day s i g n a l i n t e n s i t i e s t o b e o b t a i n e d i n poor a tmospher ic c o n d i t i o n s , and t o r a i s e p resence l i g h t i n t e n - i

s i t v t o n i a h t s i a n a l l e v e l s . - a a

17. Key Words

BRAKE LIGHTS, LIGHTING DESIGN, MOTOR VEHICLE LIGHTING, PARKING LIGHTS, REARLIGHTS, TAILLIGHTS, TAILLIGHT COLOR, TURN SIGNALS

i 1 f o r s a l e t o t h e p u b l i c !

18. Distr~bution Statement

A v a i l a b i l i t y i s u n l i m i t e d . Document I may be r e l e a s e d t o t h e Clear inghouse f o r F e d e r a l S c i e n t i f i c and Techn ica l I I n f o r m a t i o n , S p r i n g f i e l d , Va. 22151 1

19. Security Class~f.(of thls report)

u n c l a s s i f i e d

I

20. Security Classif.(of this page)

u n c l a s s i f i e d 21. No. of Pages 22. Pr~ce

$3.00

TABLE OF CONTENTS

List of Figures

List Tables

Acknowledgements

Part I.-Introduction .......................................... 1

Part II..Planning Tasks ....................................... 6 1 . Summary of the Major Findings of the Prior

Contractors .......................................... 7

2 . Conclusions Reached by the Prior Contractors ......... 9

3 . HSRI Interpretations of the Conclusions Reached by the Prior Contractors 11 ................................

4 . Accident Data ........................................ 12 5 Conclusions Based Upon Traffic Accident Analysis 16 ..... . 6 . General Conclusions .................................. 16 7 . Priority Ordering of Research Tasks .................. 17 8 . Actual Tasks to be Accomplished ...................... 19

............................. . Part III..Method Research Tasks 20

1 . Evaluation of Coding Dimensions and Functional ......................... Separation of Lamps ask 1) 20

Introduction ........................................ 20 Method .............................................. 21 The Lead Car ........................................ 21 The Following Car.. .................................. 21

Recording Equipment ............................ 26

Lighting Systems ............................... 26 ........................ The Oependent variables 28

Signal Modes ................................... 28

Turn Signal Flash Rate ......................... 28 Photometry ..................................... 28

Procedure ........................................... 28 The Effects of High Intensity, High Ratio ........... 30 The Effects of Low Intensity. High Ratio ............ 31 Results.. ........................................... 31

Reaction Time ................................. 31 ................... Signal Identification Errors 36

........................ Missed Signals Analysis 36

Signal Effectiveness Ratings ................... 39

iii

The Effect of Alcohol Upon Response to Signals ........ Given by Rear Lighting and Signaling Systems 39

................................... Introduction 39

Method ......................................... 41 Results ........................................ 43

............................. Reaction Time 43

Signal Identification Errors .............. 48 ................... Missed Signals Analysis 48

..... Rating of Signal System Effectiveness 48

2 . Determination of Intensity Values for Rear Signal ...................................... Lights (Task 2) 50

................ Day and Night Outdoor Intensity Test 53

Method ....................................... 53 ................................. Apparatus 53

................................ Photometry 55

Subject Response Indicators ............... 55 ..................... Independent Variables 57

................................... Color 57

Lamp Area ............................... 57 ........................... Lamp Location 57

........................ Ambient Lighting 57

........................ Viewing Distance 57

Visual Characteristics of the Observers ............................... 58

Subjects .................................. 58 Procedure ................................. 58

Results ...................................... 61 Dusk/Dawn Simulation Discomfort Intensity Test ...... 77

......................................... Method 77

Results ........................................ 77 Determination of Minimum and Maximum Day and Night values .............................................. 78

3 . Driver Switching and Feedback Mode Requirements for Multi-Intensity Lighting (Task 3) .................... 87

4 . Turn Signal Visibility (Task 4) ...................... 92

Longitudinal Location Analysis ...................... 92

Vertical Location Study ............................. Method ......................................... 94

Subjects .................................. 94 Procedure ...................................... 97 Results ........................................ 97

Signal Area and Intensity ........................... 101

Method ...................................... 103

Apparatus ................................. 103

Procedure...................................... 103

............ Day and Night Field Experiment 105

...... Dusk and Night Laboratory Experiment 106

Results ...................................... 106 Application of Results .................... 114

5 . A Methodology for Studying the Effect of Improved Rear Lighting Configuration on Highway Safety (Task 5) ............................................. 119

Introduction ................................... ..... 119 Principles of Analysis ......................... 119

Methodology ......................................... 121 ......................... Monte Carlo Simulation 126

........................... Description of Model 128

Procedure for Application of the Model to ................ Rear Lighting System Evaluation 129

....... Determination of Significant Differences 130

............................................. Results 132

... Interpretation of ~pplication of Methodology 132

Application to Rear Lighting Systems Using Experimentally Measured Perception Times: The Effect of Color Coding and Functional Separa- tion .......................................... 134

The Effect of Intensity. Color Coding. and Functional Separation ........................ 140

The Effect of Functional Separation. and ~unctional Separation with Color Coding ........ 140

Conclusions ......................................... 149 s

6 . Headway Change Detection as a Function of Presence Light Array (Task 6 ) ................................. 150 Simulation Studies .................................. 151

Study l...... ............................... ..153 Procedure .............................em. 1 5 3

result^.............^^........^.....^.... 157 Study 2e.e . . e m e e m e . ~ . e . . e e e e o * e a * a . * . * * * e n e e a * 157

................................. Results ..157

Study 3e..*emo.e.*.e*e.e .. ~ e * ~ e * e ~ a * e ~ * * * e e e ~ * 160

result^................^.^......^^^...... 160 ........................................ Study 4 164

................................... Results 164

Study 5 ...+...............*.e....m....... **mom164

................................... Results 166

........................................ Study 6 166

................................... Results 169

Headway Change Detection as a Function of Presence ............... Light Array in a Car Following Task.. 171

Test vehicle^^............^.^.....^....^....^.^ 171 Procedure . . . . . . . . e . e . e . . . . . e . . . . . . e e . e . . . e . e . . . 178

.......................... Independent Variables 179

........................... Dependent variables. 180

Experimental Design . . . . . . . . . . . . . . . . . .e.. .em..e. 180

result^...^.................^...............^.^ 180

7 . Coasting Signal Analysis (Task 7).. ................., 188

Introduction ..................e..m........ee....... 1 8 8

Method 1 9 0

Procedure . . . . . . . . . . . . . . . .e . . .e . . . .m. . . .eme. . . . 1 9 4

Results ........................................ 195 Part 1V.-Development of recommendation^.....+.^......+........ 217

Discussion ............e.e.......................ee....... 217

System Coding . . . . . . . . . . . . . . . . .eme. . .e . . . . . .ee. .ee. . . 217

Presence Lamp Array . . . . . . . . . . . . . . m e . . e . m . . . e . . e . e . e . 228

Side-Mounted Turn signal......^....,.....+.......... 230

Day-Night Intensity ................................. 231 Manual Intensity Switching ...........e...e......e..e 234

...................... High Intensity Presence Lights 235

............................ Lamp Separation ~istance 235

amp Location ........... ........................... 2 3 6

Coasting Signal ...................................... 237 Conslusions ............................................ 239

.................................................... Appendices 246

Appendix A-1: Multi-Intensity Study Instructions ........ 246 Appendix A-2: Cumulative Percent Day (Adequate). Night (Intolerable) Intensities. at 75 and 270 Feet. for Normal and Color-Blind Subjects. as a Function of Lamp Area and Color 2 4 9 ........................................... Appendix B: Development of a Double-Monochromator Use in Presence Light Color Evaluation Studies ............... 282 Appendix C-1: Instructions to Driver and Trip Sheet ..... 288 Appendix C-2: Program Oescription of Coasting Signal Analysis Magnetic Tape Data Processing System ............ 290

.................................................... References 297

vii

viii

LIST OF FIGURES

Figure Page

1.1 The test lamps, color and neutral filter, and disper- sion lens.......~..d...............d..~,,d,d,,,,,.,..... 22

1.2 Calibration and control instrumentation in lead car..... 23

1.3 Lead car and following car lighting system control, subject response and data recording instrumentation block ................................................. diagram 24

1.4 The part-task lights on the hood of the following car and the test lamp arrangement on the lead car........... 25

1.5 The arrangement in the following car, showing subjects' response switches and data recording equipment .......... 27

1.6 The lighting configurations. P = Presence (tail light), s = Stop, T = Turn, R = Red, A = Amber, G = Green-blue.. 2 9

2.1 Arrangement of the test lamps behind the surround b o a r d . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

2.2 Lamp intensity calibration and control system and data chart recorder................................... 56

.................. 2.3 Spectral distribution of color filters 58

2.4 Luminance ratio for day and night intensities as a function of area...................................... 73

2.5 Summary of constants LA, I L ..... L~DAy 'NIGHT C ~ ~ ~ / ~ ~ ~ . . 82

2.6 Red, day and night minimum and maximum intensity as a function of lamp area................................... 84

2.7 Amber, day and night minimum and maximum intensit.y as a function of lamp area................................. 85

2.8 Green-blue, day and night minimum and maximum intensity as a function of lamp area.....,..,..................... 86

3.1 Suggested legend and type of switch operation for manual intensity override... ............................ 90

4.1 Traffic situation depicting vehicles abreast of each other in the first and third lanes of a triple lane highway ................................................ 93

Figure

4.2 Traffic situation depicting the case in which a rear mounted turn signal on vehicle "T" would be obscured to a driver of a vehicle in the passing lane, and showing the increased field of view provided by the side mounted turn signal ................................ 95

4.3 Driver's view in the passing lane....................... 96

4.4 50th and 25th percentile rightside visibility profiles for subjects in 1969 Chevrolet Camaro...............,... 98

4.5 50th and 25th percentile rightside visibility profiles ... for subjects in 1969 Chevrolet Chevelle,............. 99

4.6 50th and 25th percentile rightside visibility profiles ... for subjects in 1969 Chevrolet 100

4.7 Diagram defining radiation angles . e ~ e . e e e . e e ~ e o . . e b e e e ~ e 102

4.8 Side turn signal intensity test arrangement, showing test lamp surround and subject in the vehicle........... 104

................. 4.9 The laboratory test arrangement........ 107

4.10 The effect of distance upon angular visibility of side mounted turn signals . . . . . . e . . . . . . . . . . . . . . . . . e e m e e e ~ . e e 116

5.1 Schematic representation showing the effect of rear ........... lighting system design on highway safety..... 120

...... 5.2 Schematic representation of the traffic subsystem. 123

5.3 Crash probability for system 1 and 8 in turn-stop mode on an expressway................................... 133

5.4 Crash probability for system 1 and 8 in turn-stop mode on a two lane rural highway . e e e . . . . . . e . e e e . e , . m 135

5.5 Crash probability for system 1 and 8 in turn-stop mode on an expressway assuming an improved braking ............................................ system...... 136

5.6 Crash probability for system 1 and 8 in turn-stop mode on a two lane rural highway assuming an improved

..................................... braking system..... 137

5.7 Crash probability for system 8, high and low intensity signals, and system 1, low intensity, in the stop mode on an expressway.................................b...... 141

F i g u r e Page

5 . 8 Crash p r o b a b i l i t y f o r sys tem 8 , h i g h and low i n t e n s i t y s i g n a l s , and sys tem 1, low i n t e n s i t y , i n t h e s t o p mode on a two l a n e r u r a l highway . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142

5.9 Crash p r o b a b i l i t y f o r sys t em 8 , h i g h and low i n t e n s i t y s i g n a l s , and sys tem 1, low i n t e n s i t y , i n t h e t u r n - s t o p mode on an expressway. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143

Crash p r o b a b i l i t y f o r sys tem 8 , h i g h and low i n t e n s i t y s i g n a l s , and sys tem 1, low i n t e n s i t y , i n t h e t u r n - s t o p

. . . . . . . . . . . . . . . . . . . . . . . . mode on a two l a n e r u r a l highway

5 .11 Crash p r o b a b i l i t y f o r sys tems 1, 4 and 8 , i n t h e t u r n - s t o p mode on an expressway, t o show t h e e f f e c t of .................. f u n c t i o n a l s p e a r a t i o n and c o l o r cod ing 146

5.12 Crash p r o b a b i l i t y f o r sys tems 1, 4 and 8 i n t h e t u r n - s t o p mode on a two l a n e r u r a l highway, t o show t h e e f f e c t of f u n c t i o n a l s e p a r a t i o n and c o l o r c o d i n g . . . . . . . . 147

6 . 1 C a r r i a g e l i g h t i n g a r r a y and t a b l e and t h e s u b j e c t ' s ................................................. s t a t i o n 152

Monocular a p e r t u r e and t h e s u b s i d i a r y

f o r v iewing t a s k l i g h t s

t h e l i g h t i n g a r r a y , . . . . r e s p o n s e s w i t c h box . .

6 .3 The l o c a t i o r i of t h e s u b s i d i a r y t a s k lamps, one of which i s l i g h t e d . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155

6 . 4 Red, p r e s e n c e l i g h t a r r a y s used i n s t u d y l . . . . . . . . . . . . . . 156

.......... 6 . 5 Red, p r e s e n c e l i g h t a r r a y s used i n s t u d y 2 . . . . 159

6.6 Red, p r e s e n c e l i g h t a r r a y s used i n s t u d y 3 t o show t h e e f f e c t of h o r i z o n t a l , v e r t i c a l , and combined h o r i z o n t a l / v e r t i c a l d i s p l a y s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161

6.7 Red, p r e s e n c e i i y l r i ; a r r a y s used t o e v a l u a t e t h e e f f e c t o f t h e r a t i o of l . i g h t e d / t o t a l a r e a between lamps i n s t u d y 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163

6.8 Red, p r e s e n c e l i g h t a r r a y s used i n s t u d y 5 t o f u r t h e r e v a l u a t e h o r i z o n t a l and combined h o r i z o n t a l / v e r t i c a l ................................................ d i s p l a y s 165

6.9 Red and g reen -b lue p r e s e n c e l i g h t a r r a y s used i n s t u d y 6 ............................................... 168

Figure

6.10 Closure d e t e c t i o n v e h i c l e ins t rumenta t ion . . . . . . . . . . . . . . . 172

6.11 Lead c a r showing l a y o u t of tes t lamps. Stock v e h i c l e r e a r l i g h t s were rna~ked.............~,.................. 173

6.12 Lead c a r c o n t r o l and d a t a r ecord ing ins t rumenta t ion . .... The coun te r above t h e dash r e a d headway cont inuously 175

6.13 The p a r t - t a s k l i g h t s mounted on t h e hood of t h e fo l lowing c a r , and t h e d r i v e r ' s response swi tches on t h e da~h..............,................~...........~.... 177

6.14 The f o u r presence l i g h t a r r a y s used i n t h e v e h i c l e ........... headway change d e t e c t i o n tes t . . . . . . . . . . . . , . . . 181

6.15 The e f f e c t of lamp a r r a y upon Weber r a t i o s a t t h r e e headway dis tances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187

Vehicle ins t rumenta t ion f o r c o a s t i n g s i g n a l a n a l y s i s . . . .

7.2 Coas t ing d a t a r ecord ing i n s t r u m e n t a t i o n . . . . . . . . . . . . . . . . . 192

7.3 Cumulative p e r c e n t c o a s t i n g t ime d i s t r i b u t i o n , a c c e l e r a t o r r e l e a s e followed by a c c e l e r a t o r a p p l i c a t i o n , ................................ i n f o u r speed c a t e g o r i e s 199

7.4 Cumulative p e r c e n t c o a s t i n g t ime d i s t r i b u t i o n , a c c e l e r a t o r r e l e a s e fol lowed by brake a p p l i c a t i o n , ................................ i n f o u r speed c a t e g o r i e s 200

7.5 Cumulative p e r c e n t c o a s t i n g time d i s t r i b u t i o n s f o r brake r e l e a s e fol lowed by a c c e l e r a t o r and brake a p p l i c a - t i o n , i n f o u r speed c a t e g o r i e s .......................... 201

7 .6 Cumulative p e r c e n t change i n speed, a c c e l e r a t o r r e l e a s e fol lowed by a c c e l e r a t o r a p p l i c a t i o n , i n f o u r speed c a t e g o r i e s . . ............................................ 203

7.7 Cumulative pe rcen t change i n speed d i s t r i b u t i o n , a c c e l e r a t o r r e l e a s e fol lowed by brake a p p l i c a t i o n , f o r f o u r speed c a t e g o r i e s .............................. 204

7.8 Cumulative p e r c e n t change i n speed d i s t r i b u t i o n , brake r e l e a s e fol lowed by a c c e l e r a t o r and brake a p p l i c a t i o n , f o r f o u r speed c a t e g o r i e s ............................... 205

7.9 Cumulative pe rcen t change i n headway d i s t r i b u t i o n , a c c e l e r a t o r r e l e a s e fol lowed by a c c e l e r a t o r a p p l i c a t i o n , . . . . . . . . . . . . . . . . . . . . . . . . . . . f o r f o u r speed c a t e g o r i e s . , . . 207

Fisure Paae

7.10 Cumulative percent change in headway distribution, accelerator release followed by brake application, for four speed categories .............................. 208

7.11 Cumulative percent change in headway distribution, brake release followed by accelerator and brake application, for four speed categories .................. 209

7.12 Cumulative percent coasting time distribution across driver actions, for four speed categories ........,...... 212

7.13 Cumulative percent change in speed distribution, ........ across driver actions, for four speed categories 213

7.14 Cumulative percent change in headway distribution, ........ across driver actions, for four speed categories 214

B.1 Ray path diagram in one line of double monochromator.... 284

B.2 Double monochromator with power supply .............,.... 285

B . 3 Double monochromator with side cover removed............ 287

C-2.1 Tape processing interface diagram for coasting signal .............................................. analysis 291

xiii

L I S T OF TABLES

T a b l e - Page

1. PERCENT OF FATAL ACCIDENTS INVOLVING L I K E ORIENTED VEHICLES (1967)....,................,e....e....~..e. 1 3

2 . PERCENT DISTRIBUTION OF FATAL ACCIDENTS FOR L I K E O R I E N T E D V E H I C L E S ONLY (1967)....,.........,.......... 1 3

3. NUMBER OF F A T A L I T I E S I N L I K E ORIENTED VEHICLE ACCIDENTS (1967)...................b...........e..e 1 3

4 . PERCENT OF ALL ACCIDENTS INVOLVING L I K E ORIENTED VEHICLES (1967)......,............~.,......,.,. 1 4

5. PERCENT DISTRIBUTION OF ALL ACCIDENTS FOR L I K E ............... O R I E N T E D V E H I C L E S O N L Y ( 1 9 6 7 ) . . . . . . . . . . 1 4

6. NUMBER OF L I K E ORIENTED ACCIDENTS ( 1 9 6 7 ) . . . . . . , . . . , . . . 1 4

1.1 ANALYSIS OF VARIANCE OF REACTION TIME TO SIGNALS. DATA FOR 80 SUBJECTS, I N 1 / 1 0 0 0 SECONDS T N S F O R M E D TO LOG, ............................................... 32

1 . 2 GEOMETRIC MEAN REACTION TIME FOR MAIN E F F E C T S . . . , . . . , . 33

1 . 3 GEOMETRIC MEAN REACTION TIME (SECONDS) FOR EACH SYSTEM AND SIGNAL MODE I N THE HIGH AND LOW I N T E N S I T Y C I T Y DRIVING T E S T S , FOR 8 0 SUBJECTSboo . . e . o . 0 0 0 - 0 0 0 0 0 . 35

1 . 4 GEOMETRIC MEAN REACTION TIME AS A FUNCTION OF TASK ANDMODE. DATAARE I N S E C O N D S . . . . . . . . . . . . . . . . . . . . . . . . 35

1 . 5 NUMBER OF ERRORS I N SIGNAL I D E N T I F I C A T I O N . DATA ................................... FOR 4 0 PASSENGERS.. 3 7

1 . 6 NUMBER OF MISSED SIGNALS. DATA FOR 8 0 S U B J E C T S , . . . . . . 38

1 . 7 MEAN SIGNAL EFFECTIVENESS RATINGS FOR EACH SYSTEM, I N T E N S I T Y AND TASK....,.....................,..,.. 40

1 . 8 INDIVIDUAL COMPARISONS OF MEAN SYSTEM SIGNAL EFFECTIVENESS RATING BY NEWMAN-KEULS T E S T . . . . . . . . . . . . . 4 0

1 . 9 ANALYSIS OF VARIANCE OF REACTION TIME TO SIGNALS FOR TWO REAR LIGHTING SYSTEMS, WITH AND WITHOUT ALCOHOL. DATA FOR 3 2 S U B J E C T S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 4 , 4 5

Table - P a g e

1 . 1 0 GEOMETRIC MEAN RElACTION TIME (SECONDS) TO LIGHTING SYSTEMS AND SIGNAL MODES, DATA FOR 3 2 S U B J E C T S . . , . , . , 4 6

1.11 GEOMETRIC MEAN REACTION TIME (SECONDS) FOR SYSTEMS AND SEX OF SUBJECT I N THE ALCOHOL EXPERIMENT. DATA FOR 32 S U B J E C T S a o o o a o * o . . a . . o o * o . o o ................... 4 6

1 . 1 2 GEOMETRIC MEAN REACTION TIME (SECONDS) AS A FUNCTION OF SEX, TASK, ALCOHOL DOSE, AND SYSTEM. DATA FOR 3 2 S U B J E C T S . . * . . . o . o . o . . . * . a * e o * o m * * * * * o e o o a 47

1.13 RELATIVE IMPAIRMENT ( R I ) I N REACTION TIME DUE TO ALCOHOL DOSE FOR SEX AND SYSTEM, CONTROLLED FOR ORDER EFFECTS....,.,,a..,.~.~~~~.~,,.....,,.......... 47

1 . 1 4 NUMBER OF ERRORS I N SIGNAL I D E N T I F I C A T I O N FOR .......... SYSTEMS AND DOSES, DATA FOR 1 6 SUBJECTS. . . . 4 9

1.15 NUMBER OF MISSED SIGNALS FOR SYSTEMS, MODES AND DOSES. DATA FOR 32 SUBJECTS.,....,......,.,..,..,,,,..,.. 49

2 . 1 8 5 t h PERCENTILE INTENSITY AND LUMINANCE VALUES JUDGED ADEQUATE BY 37 COLOR-NORMAL SUBJECTS FOR EACH COLOR, LAMP AREA, AND VIEWING DISTANCE I N THE DAY. 63

2 . 2 85 th PERCENTILE INTENSITY AND LUMINANCE VALUES JUDGED ADEQUATE BY 1 0 COLOR-BLIND SUBJECTS FOR EACH COLOR, LAMP AREA, AND VIEWING DISTANCE I N THE D A Y . . . . . , . , . . . , 6 4

2 . 3 1 5 t h PERCENTILE INTENSITY AND LUMINANCE VALUES JUDGED INTOLERABLE BY 3 2 COLOR-NORMAL SUBJECTS FOR EACH COLOR, LAMP AREA, AND VIEWING DISTANCE AT NIGHT. m e .. 6 6

2 . 4 1 5 t h PERCENTILE INTENSITY AND LUMINANCE VALUES JUDGED INTOLERABLE BY 8 COLOR-BLIND SUBJECTS FOR EACH COLOR, LAMP AREA, AND VIEWING DISTANCE AT N I G H T . , , . . . . . . . , . . , 6 7

2 . 5 LUMINANCE RATIOS FOR COLORS (AND W H I T E ) , DISTANCE, NORMAL AND COLOR BLIND SUBJECTS, DAY AND N I G H T . . . . . . . . 70

2 . 6 MEAN LUMINANCE RATIOS FOR COLORS, AND FOR NORMAL AND COLOR-BLIND SUBJECTS, OVER VIEWING D I S T A N C E . . . . . . . . . .. 7 0

2 . 7 LUMINANCE RATIO AS A FUNCTION OF LAMP AREA ACROSS COLOR AND DISTANCE FOR NORMAL AND COLOR-BLIND SUBJECTS FOR DAY AND NIGHT C R I T E R I A . . . . . . . . . . . . . . . . , . . . . . . . . , . . 7 2

2 . 8 THE EFFECTS OF VIEWING DISTANCE UPON DAY ( 8 5 t h PER- C E N T I L E ) ' AiiD NIGHT (15 th PERCENTILE) LUMINANCE RATIOS FOR NORMAL XND COLOR BLIGD S U B J E C T S . . , , . . . . . . . . . , . . . . . 72

Table - Page

2.9 MEAN 85th PERCENTILE DAYTIME CP VALUES OBTAINED FROM TABLE 2.1 BY AVERAGING OVER DISTANCE.............

2.10 50th PERCENTILE CANDLEPOWER VALUES FOR DUSK/DAWN SIMULATION, DAY AND NIGHT OUTDOOR TESTS, FOR RED AND ........... GREEN-BLUE, AND THREE AREAS, AT 75 FEET,.,.

2.11 25th PERCENTILE INTENSITY VALUES JUDGED INTOLERABLE BY 32 COLOR-NORMAL SUBJECTS FOR EACH COLOR, AND LAMP AREA, AT 75 F E E T o o . o e . e . . . . . . . e . . . * e m e e m e . o e * e a e o

2.12 RATIO OF 25th PERCENTILE NIGHT/85th PERCENTILE DAY CANDLEPOWER VALUES FOR EACH AREA..................

4.1 DAY MINIMUM, ADEQUATE, AND MAXIMUM CANDLEPOWER PERCENTILES FOR THREE LAMP AREAS, TWO VIEWING DISTANCES, AND THREE FIXATION ANGLES. FIELD STUDY DATA FOR 30 S U B J E C T S e . . e o e e e e . e e e * e o e e e * a , . e . a e . e e e e e .

4.2 DUSK MINIMUM, ADEQUATE, AND MAXIMUM CANDLEPOWER PERCENTILES FOR THREE LAMP DIAMETERS, TWO VIEWING DISTANCES, AND THREE FIXATION ANGLES. LABORATORY STUDY DATA FOR 30 SUBJECTS............e.e.e.....e.....

4.3 DUSK MINIMUM, ADEQUATE, AND MAXIMUM CANDLEPOWER PERCENTILES FOR THREE LAMP DIAMETERS, TWO VIEWING DISTANCES, AND THREE FIXATION ANGLES. FIELD TEST ......................... STUDY DATA FOR 30 SUBJECTS...

4.4 NIGHT MINIMUM, ADEQUATE, AND MAXIMUM CANDLEPOWER PERCENTILES FOR THREE LAMP DIAMETERS, TWO VIEWING DISTANCES, AND THREE FIXATION ANGLES. LABORATORY STUDY DATA FOR 30 SUBJECTS............................

4.5 NIGHT MINIMUM, ADEQUATE, AND MAXIMUM CANDLEPOWER PERCENTILES FOR THREE LAMP DIAMETERS, TWO VIEWING DISTANCES, AND THREE FIXATION ANGLES. FIELD PILOT STUDY WITH 9 SUBJECTS.................................

4.6 90th PERCENTILE MINIMUM VISUAL THRESHOLDS (IN CANDLES) IN DUSK AND DAY CONDITIONS FOR TWO LAMP DIAMETERS, TWO VIEWING DISTANCES, AND THREE FIXATION ANGLES..........

4.7 MINIMUM AND MAXIMUM INTENSITIES IN DAY AND NIGHT CONDITIONS FOR TWO LAMP AREAS, 5'-90' H LEFT OR RIGHT, FOR A DUAL-INTENSITY, SIDE MOUNTED, AMBER TURN SIGNAL.

Table Page

4.8 MINIMUM AND MAXIMUM INTENSITIES FOR TWO LAMP AREAS, 5'-90' H LEFT OR RIGHT, FOR A SINGLE-INTENSITY, SIDE MOUNTED AMBER TURN SIGNAL..................,,.,.. 115

5.1 EFFECT OF COLOR CODING WITH FUNCTIONAL SEPARATION..... 138

5.2 EFFECT OF 1N.TENSITY AND COLOR CODING WITH FUNCTIONAL SEPARATION.,...,,.,..........,....,,,,,.,.,,,,,,,e 145

5.3 EFFECT OF FUNCTIONAL SEPARATION, AND FUNCTIONAL SEPARATION WITH COLOR CODING.,....,,..........,....,,. 148

6.1 STUDY 1: GEOMETRIC MEAN DISPLACEMENT FOR EACH ARRAY. DATA FOR 12 SUBJECTS..,...,,......,........... 158

6.2 STUDY 1: ANALYSIS OF VARIANCE OF DISPLACEMENT V A L U E S . . . , . . . . . , . . . . . . . . . , . . . . , . ~ , . , ~ . . . . . . , . . . . . . . . 158

6.3 STUDY 2: GEOMETRIC MEAN DISPLACEMENT FOR THREE A R M S . DATA FOR 12 SUBJECTS.......,.,,....,...,..... 162

6.4 GEOMETRIC MEAN DISPLACEMENT FOR EACH ARRAY USED IN STUDY 3. DATA FOR 25 SUBJECTS..................,..... 162

6.5 STUDY 4: GEOMETRIC MEAN DISPLACEMENT FOR ARRAYS DIFFERING IN LIGHTED AREA/TOTAL AREA. DATA FOR 12 S U B J E C T S . . . . . , , . . . , . , . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167

6.6 GEOMETRIC MEAN DISPLACEMENTS FOR EACH OF THREE ARRAYS USED IN STUDY 5 . . . . . , , . . . . . . . . . . . , . . . . , . . . . . . . . . . . , . . , 167

6.7 STUDY 6: MEDIAN DISPLACEMENTS FOR RED AND GREEN-BLUE DISPLAYS FOR APPROACHING AND RECEDING TRIALS. DATA FOR 18 SUBJECTS, ALL COLOR NORMAL....,................ 170

6.8 STUDY 6: MEAN RANKING OF EACH ARRAY IN EACH COLOR FOR 18 SUBJECTS......,................................ 170

6.9 ANALYSIS OF VARIANCE OF THE CHANGE IN HEADWAY FOR 200 FEET AND 300 FEET INITIAL HEADWAY DISTANCES. DATA .................................... FOR SUBJECTS 1-12, 183

6.10 ANALYSIS OF VARIANCE OF THE CHANGE IN HEADWAY FOR 300 FEET AND 400 FEET INITIAL HEADWAY DISTANCTS. DATA .................................. FOR SUBJECTS 13-24.. 184

6.11 RESULTS OF NEWMAN-KEULS TEST IN CHANGE IN HEADWAY MEANS, AT EACH INTITAL HEADWAY, FOR EACH ARRAY........ 186

Table P a g e

6 . 1 2 MEDIAN CHANGE I N HEADWAY (AH FEET) AS A FUNCTION OF INITIAL HEADWAY FOR ONE, TWO? THREE AND FOUR LAMP ARRAYS, AND MEAN EFFECTIVENESS RATINGS.. . . . . . . . . . . . . .. 1 8 6

6 . 1 3 WEBER RATIOS (AH/H) FOR DETECTION OF CHANGE I N HEADWAY FOR TWO, THREE AND FOUR LAMP ARRAYS........... 186

7 . 1 PERCENT OF EACH DRIVER CONTROL ACTION IN FOUR SPEED CATEG0R1ES.................................... 1 9 6

7 . 2 9 0 t h PERCENTILE COASTING TIME, CHANGE I N SPEED AND CHANGE I N HEADWAY I N FOUR SPEED RANGES FOR FOUR .............................. DRIVER CONTROL ACTIONS.. 2 1 0

A-2.1-2.32 CUMULATIVE PERCENT DAY (ADEQUATE) INTENSITIES, NIGHT (INTOLERABLE) INTENSITIES, AT 75 AND 270 FEET, FOR NORMAL AND COLOR-BLIND SUBJECTS? AS A FUNCTION OF LAMP AREA AND COLOR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250

x v i i i

ACKNOWLEDGEMENTS

T h i s r e s e a r c h program i n v e h i c l e r e a r l i g h t i n g and s i g n a l -

i n g was conducted by s t a f f drawn from f o u r depa r tmen t s a t t h e

Highway S a f e t y Research I n s t i t u t e : Human F a c t o r s , P h y s i c a l

F a c t o r s , Systems A n a l y s i s and Computer S e r v i c e s .

The program was under t h e d i r e c t i o n o f D r , R,G. Mortimer,

Human F a c t o r s depa r tmen t , who was r e s p o n s i b l e f o r p l a n n i n g and

e x e c u t i o n of t h e r e s e a r c h t a s k s and t h e f i n a l r e p o r t .

The e l e c t r o n i c equipment d e s i g n and c o n s t r u c t i o n was t h e

r e s p o n s i b i l i t y of Mr. J. Campbell. Mechanical e n g i n e e r i n g was

c a r r i e d o u t by M r . J . Wirth . Equipment was c o n s t r u c t e d and

d e s i g n e d , whol ly o r i n p a r t , by Messrs. I, Rudolph, G. Popp

and R, S t e i n of t h e P h y s i c a l F a c t o r s depar tment .

Mr. W. C a r l s o n , Systems A n a l y s i s depa r tmen t , was r e s p o n s i b l e

f o r t h e development and a n a l y s i s of t h e c a r - f o l l o w i n g , s i g n a l

system e v a l u a t i o n model.

Mr. R. Murphy, P h y s i c a l F a c t o r s depa r tmen t , and Mrs. C . Hafner ,

Computer S e r v i c e s depa r tmen t , were r e s p o n s i b l e f o r e x e c u t i n g t h e

n e c e s s a r y programs f o r t h e c o a s t i n g s i g n a l d a t a a n a l y s i s f o r t h e

HSRI h y b r i d computer.

Mr. D. P o s t , Human F a c t o r s depa r tmen t , was invo lved i n p l an -

n i n g and d a t a c o l l e c t i o n of t h e s i g n a l sys tem and a l c o h o l e x p e r i -

ments , and t h e lamp a r e a - i n t e n s i t y tes ts and d a t a a n a l y s i s .

M r . A. P o s k o c i l , Human F a c t o r s depa r tmen t , was r e s p o n s i b l e f o r t h e

t u r n s i g n a l v i s i b i l i t y a n a l y s i s and exper iments .

Messrs. C . Moore and T . VanderMey, Human F a c t o r s depa r tmen t ,

were r e s p o n s i b l e f o r c o n s t r u c t i o n of t h e s i m u l a t i o n f o r t h e

headway change d e t e c t i o n exper iments . They a l s o r a n t h e tes t

s u b j e c t s i n t h e s i g n a l sys tem e v a l u a t i o n s , t h e lamp a r e a - i n t e n s i t y

tes ts , t h e s i m u l a t o r t es t s and t h e v e h i c l e t e s t s of r e a r l i g h t i n g

a r r a y s , and c a r r i e d o u t some d a t a a n a l y s e s .

D r . J. Lower, Human Factors department, was responsible

f o r much of t he computer da t a analyses f o r many phases of t h e

program, and a s s i s t e d i n planning and da t a c o l l e c t i o n i n t he

a lcohol experiment.

A r t work was c a r r i e d ou t by M r . T. O'Brien and Mrs. R. Girard

and e d i t i n g by Mrs. J. Raymond.

Mrs. M. Damberg and Mrs. S. P o t t s , Human Factors department,

were responsible f o r s e c r e t a r i a l s e rv i ces assoc ia ted wi th t h e

p ro j ec t .

The p r o j e c t monitor was Mr. V. J. Esposito, NTSI. He and

M r . I,. Owens, MVSPS, made c r e a t i v e and c r i t i c a l suggest ions and

were h e l p f u l i n o the r ways i n t h i s program.

F ina l ly , the work could no t have been completed without

about 500 male and female t e s t sub jec t s who each p a r t i c i p a t e d

f o r up t o s i x hours i n p i l o t s t u d i e s and the experiments.

x x i i

PART INTRODUCTION V e h i c l e rearward l i g h t i n g h a s been an e v o l u t i o n a r y p roces s

s i n c e t h e i n t r o d u c t i o n of t h e motor c a r , The f i r s t s t o p l i g h t

appeared i n 1906 (Ki lgour , 1962) and s i n c e t h a t time t h e r e have

been g r a d u a l improvements and changes i n r e a r l i g h t i n g and s i g -

n a l i n g . These developments hinged upon t e c h n o l o g i c a l advances

i n means f o r producing l i g h t s from t h e e a r l y oxy-ace ty lene lamps

t o t h e e l e c t r i c , t u n g s t e n f i l a m e n t b u l b and w i t h t h e r e c o g n i t i o n

f o r improved marking and s i g n a l i n g o f v e h i c l e s a s t h e d e n s i t y of

t r a f f i c i n c r e a s e d .

V e h i c l e r e a r l i g h t i n g p r o v i d e s what h a s been termed augment-

i n g cues (Mortimer, 1967) t o d r i v e r s , i n t h e s ense t h a t it aug-

ments t h e pr imary cues provided by t h e v e h i c l e i t s e l f a s seen

a g a i n s t i t s background i n o r d e r t o a i d d r i v e r s i n making d e c i -

s i o n s concern ing t h e l o c a t i o n , v e l o c i t y and d e c e l e r a t i o n , i n t e n -

t i o n t o t u r n , e t c . of v e h i c l e s s een i n f r o n t of him. Augmenting

cues p rov ide added in fo rma t ion t o d r i v e r s t o a i d them i n making

r e l e v a n t d e c i s i o n s w i t h r e g a r d t o o t h e r v e h i c l e s . Not o n l y do

augmenting cues a i d t h e d r i v e r i n d e t e c t i n g t h e p re sence of

a n o t h e r v e h i c l e , such a s by i t s p re sence ( t a i l ) l i g h t s a t n i g h t ,

b u t t h e y a l s o p rov ide warning of impending changes i n t h e s t a t u s

of a l e a d v e h i c l e , and have a c a p a b i l i t y o f p rov id ing advance

in fo rma t ion of t h e i n t e n t i o n of t h e d i r e c t i o n t o b e t a k e n by a

l e a d v e h i c l e , such a s by t h e t u r n s i g n a l , which cannot be pro-

v i d e d by pr imary c u e s a l o n e . Fur thermore , augmenting c u e s may

be a b l e t o p rov ide i n f o r m a t i o n t o d r i v e r s when pr imary c u e s a r e

obscured a s i n poor v i s i b i l i t y c o n d i t i o n s .

The i n c l u s i o n of marking l i g h t s and s i g n a l lamps on v e h i c l e s

fo l lowed a s a r e s u l t of t h e r e c o g n i t i o n of t h e r o l e of augment-

i n g c u e s i n t r a f f i c s a f e t y . Veh ic l e marking t o t h e r e a r has been

g r a d u a l l y improved a s shown by changes i n t h e i n t e n s i t y of p r e s -

ence l i g h t s (Moore and Ruffe l -Smi th , 1966) and i n c r e a s i n g t h e

number of lamps used f o r t h i s f u n c t i o n from a s i n g l e presence

l i g h t , g e n e r a l l y mounted i n t h e c e n t e r of t h e v e h i c l e , t o two

presence l i g h t s mounted a t t h e l e f t and r i g h t edge of t h e r e a r

of t h e v e h i c l e . Changes of t h i s type which would r e s u l t i n

improved p e r c e p t i o n of a v e h i c l e a t n i g h t a s w e l l a s i n e s t i -

mating t h e d i s t a n c e and c l o s u r e r a t e f o r a fo l lowing d r i v e r have

r e s u l t e d i n a r e d u c t i o n of rear -end a c c i d e n t s (Moore and R u f f e l l -

Smith, 1966) .

A comparison of t h e marking and s i g n a l i n g system of v e h i c l e s

c o n s t r u c t e d o n l y f i v e y e a r s ago w i t h t h o s e p r e s e n t l y be ing manu-

f a c t u r e d show c o n s i d e r a b l e f u r t h e r improvements i n v e h i c l e

l i g h t i n g and t h i s i s exempl i f ied by SAE Recommendation J-575

which has been l a r g e l y incorpora ted w i t h some r e v i s i o n s i n Depart-

ment of T r a n s p o r t a t i o n , Motor Veh ic le S a f e t y Performance Standard

No. 108 (1969) . This s t a n d a r d s t i p u l a t e s requi rements f o r v e h i c l e

l i g h t i n g f o r a l l c l a s s e s of motor v e h i c l e s i n terms of t h e

l o c a t i o n , a r e a , i n t e n s i t y and f u n c t i o n a l a s p e c t s of t h e v e h i c l e

l i g h t i n g system.

Other c o u n t r i e s , p a r t i c u l a r l y A u s t r a l i a and Western European

n a t i o n s , have a l s o developed automotive s t a n d a r d s a f f e c t i n g l i g h t -

ing . A review of t h e s e s t a n d a r d s i n d i c a t e s s u b s t a n t i a l d i f -

f e r e n c e s i n t h e requi rements i n v a r i o u s a r e a s of t h e s t a n d a r d s ,

f o r example, i n t h e angu la r d i s t r i b u t i o n p a t t e r n of l i g h t emi t t ed

by marking and s i g n a l i n g lamps. These d i f f e r e n c e s r e f l e c t a

d ive rgence of op in ion on t h e requi rements f o r t h e o p e r a t i o n a l

and o t h e r c h a r a c t e r i s t i c s of marking and s i g n a l i n g systems and

t h e y impose a s i g n i f i c a n t burden upon t h e v e h i c l e manufacturers

who seek t o have t h e i r v e h i c l e s accepted i n t h e s e n a t i o n s . The

f a c t t h a t such d i f f e r e n c e s e x i s t , however, i n d i c a t e a l s o t h a t

t h e requi rements f o r v e h i c l e marking and r e a r s i g n a l i n g have no t

been f i n a l l y de termined, i n t h e sense t h a t a l l in fo rmat ion r e l a t -

ing t o t h e s e t t i n g of a p p r o p r i a t e s t a n d a r d s i s n o t y e t a v a i l a b l e .

I n t h e United S t a t e s v e h i c l e r e a r l i g h t i n g and s i g n a l i n g

c o n s i s t s , fundamental ly, of t h e fol lowing:

(1) Presence ( t a i l ) l i g h t s t o provide rearward marking.

( 2 ) Red s t o p l i g h t s which a r e produced by an i n c r e a s e

i n i n t e n s i t y of t h e presence l i g h t s t o i n d i c a t e t h a t

t h e d r i v e r has depressed t h e brake pedal a s u f f i c i e n t

d i s t a n c e t o c l o s e t h e c o n t a c t s of t h e s t o p l i g h t swi tch .

( 3 ) Red t u r n s i g n a l s produced by an i n c r e a s e i n i n t e n s i t y and

a f l a s h i n g ( o r sequencing) of t h e presence l i g h t s t o

i n d i c a t e a t u r n t o t h e l e f t o r r i g h t .

( 4 ) Red hazard warning l i g h t s , provided by o p e r a t i n g t h e

t u r n s i g n a l s on both s i d e s of t h e v e h i c l e .

( 5 ) White, back-up lamps t o provide i l l u m i n a t i o n t o t h e r e a r

of t h e v e h i c l e when i t i s i n r e v e r s e gear .

There fo re , it should be noted t h a t t h e p r i n c i p a l l i g h t cod-

ing techniques used f o r marking and s i g n a l i n g involve t h e use of

l i g h t s which vary i n i n t e n s i t y t o g i v e a s t o p o r t u r n s i g n a l and

which a r e e i t h e r s teady-burning a s i n t h e c a s e of t h e s t o p s i g n a l

o r f l a s h i n g a s i n t h e c a s e of t h e t u r n s i g n a l and hazard warning

s i g n a l . The back-up l i g h t s a r e coded by t h e a d d i t i o n of whi te

l i g h t s . I n most s t a t e s i n t h e U.S. t u r n s i g n a l s may be amber and

i n some s t a t e s s t o p s i g n a l s may a l s o be amber. The p r a c t i c e of

us ing amber f o r t h e t u r n s i g n a l i s a s t andard requirement i n

A u s t r a l i a and i s useu i n European c o u n t r i e s . No U.S. manufacturer

p r e s e n t l y uses c o l o r coding f o r t h e major s i g n a l s t h a t a r e now

g iven , i . e . t h e s t o p o r t u r n s i g n a l . I n t h e U.S., t h e r e f o r e , t h e

t u r n and s t o p s i g n a l s which a r e by f a r t h e most f r e q u e n t l y used

(compared t o t h e back-up and hazard warning s i g n a l s ) a r e coded by

an i n t e n s i t y change and f l a s h i n g . I t has a l r e a d y been i n d i c a t e d

elsewhere (Mortimer, 1968) t h a t v i s u a l d i s p l a y s may be s u i t a b l y

enhanced i n t h e i r informat ion and a t t e n t i o n - g e t t i n g va lue by t h e

use of o t h e r codes, such a s number o r c o l o r coding, and f o r t h e s e

r e a s o n s i t seems probable t h a t f u r t h e r improvements i n r e a r l i g h t i n g

and s i g n a l i n g can be made f o r fo l lowing d r i v e r s .

From another viewpoint it is important to assess the informa-

tional content of current rear lighting systems, It is question-

able whether current systems are providing the most appropriate

types of augmenting cues not only for attracting attention, which

has already been discussed, but also for providing drivers with

direct information of the status of a leading vehicle and its

intentions.

Thus, both the attention-getting value or alerting charac-

teristics and the informational content or meaning of signals

presented to the rear of automotive vehicles require further

consideration since it seems plausible to assume that improve-

ments in both of these aspects of rear lighting and signaling

will result in improved performance of drivers and, therefore,

a reduction in accidents and an increase in the quality of

traffic flow.

A fairly large research program was recently undertaken by

the Department of Transportation to study some of these questions

of vehicle rear lighting system performance. This work was be-

gun in 1967 with the granting of contract funds to a number of

independent investigators whose purpose was to develop improved

rear lighting systems (contract nos. FH-11-6551, FH-11-6552,

FH-11-6553, Fh-11-6558) and to develop "an improved understanding

of the technicality and problems of implementation associated

with the intrcduction of new rear lighting standards and the im-

pact of lighting system changeover," (FH-11-6542). Another con-

tract (FH-11-6602) had as its objective the "development and im-

plementation of plans for comparing, combining and integrating

alternative rear lighting systems, and cross-validation of the

synthesized systems," (Department of Transportation Request for

Proposal, RFP-75, May 1968).

As a result of the above work two further contracts were

let in 1968 (FH-11-6937, FH-11-6963). This report presents a

description of the work carried out and of the findings under

the latter contract, The contractual period for this study was

from 1 July 1968 to 1 December 1969. Parenthetically, it

should be noted that the project could not be started prior to

a technical meeting with NHSB staff which took place on 31 July

1968. The total duration of the project was therefore 15 months.

PART I I I METHOD--PLANN I NG TASKS The i n i t i a l t a s k s c a r r i e d o u t i n t h i s r e sea rch program

c o n s i s t e d of a review and a n a l y s i s of t h e f i n a l r e p o r t s of t h e

four c o n t r a c t o r s who had c a r r i e d o u t r e s e a r c h i n v e h i c l e r e a r

l i g h t i n g i n t h e p r i o r y e a r , The f i n a l r e p o r t s from a l l four

c o n t r a c t o r s (Contrac t Nos, FH-11-6552, FH-11-6558, FH-11-6553,

FH-11-6551) were rece ived w i t h i n t h e f i r s t t h r e e months of t h i s

program, I t was necessary t h a t t h e s e r e p o r t s were thoroughly

read and an a n a l y s i s of t h e major f i n d i n g s be provided. This

work was obviously t o form one impor tant g u i d e l i n e f o r neces-

s a r y a d d i t i o n a l r e sea rch t o be c a r r i e d o u t under t h e p r e s e n t

program, The major conclus ions t h a t were reached by t h e con-

t r a c t o r s were then summarized; and t h i s was followed by a f u r -

t h e r s e t of conclus ions of t h e i r f i n d i n g s which was based upon

our own i n t e r p r e t a t i o n s of t h e major r e s u l t s which they presen-

t ed .

A review of t r a f f i c a c c i d e n t d a t a was a l s o c a r r i e d o u t i n

o r d e r t o a s c e r t a i n t h e r o l e of rear-end c o l l i s i o n s a s a problem.

The d a t a were a l s o s c r u t i n i z e d i n o r d e r t o determine whether

f u r t h e r u s e f u l informat ion was conta ined i n a c c i d e n t d a t a which

may provide some i n s i g h t s i n t o t h e s i t u a t i o n s t h a t l e a d d r i v e r s

t o i n c u r rear-end c o l l i s i o n s and t o permit i n f e r e n c e s t o be made

f o r t h e informat ion requirements of r e a r l i g h t i n g systems.

Based upon t h e r e s u l t s of t h e p r i o r f o u r c o n t r a c t o r s , t h e

a n a l y s i s of a c c i d e n t d a t a a s w e l l a s o t h e r r e sea rch r e s u l t s con-

cerned wi th r e a r l i g h t i n g systems r e s e a r c h , a p r i o r i t y o r d e r i n g

of remaining r e s e a r c h t a s k s which could l e a d t o t h e development

of improved r e a r l i g h t i n g systems was made.

On t h e b a s i s of t h e p r i o r i t y o r d e r i n g a s e t of work p lans

were drawn up d e s c r i b i n g t h e r e s e a r c h t a s k s which it would be

proposed t o accomplish dur ing t h e resea rch program and which

would meet a s many of t h e impor tant t a s k s which were l i s t e d i n

t h e resea rch t a s k p r i o r i t y o r d e r i n g a s p o s s i b l e . A b r i e f i n g

was h e l d between NHSB p r o j e c t s t a f f and HSRI r e s e a r c h e r s a t

which t h e f i n d i n g s of t h e reviews and ana lyses of t h e previous

work, t h e a c c i d e n t a n a l y s i s , t h e p r i o r i t y t a s k o r d e r i n g , and

t h e recommended r e s e a r c h t a s k s and t h e i r d e s c r i p t i o n s were pre-

s e n t e d and d i scussed . Following NHSB s t a f f approval of t h e Work

Plan submit ted t o them t h e a c t u a l r e s e a r c h a c t i v i t i e s were go t

underway.

I n t h i s s e c t i o n a l l t h e p lanning a c t i v i t i e s t h a t have been

mentioned above a r e desc r ibed i n g r e a t e r d e t a i l and i n d i c a t e

t h e p lanning t a s k s t h a t were c a r r i e d o u t p r i o r t o t h e commence-

ment of a c t u a l exper imenta t ion .

1, SUMMARY OF THE MAJOR FINDINGS OF THE PRIOR CONTRACTORS

The f i n d i n g s t h a t a r e b r i e f l y o u t l i n e d below a r e concerned

only wi th t h e r e s e a r c h s t u d i e s t h a t were c a r r i e d o u t by t h e

p r i o r c o n t r a c t o r s and i n d i c a t e t h e r e s u l t s of those s t u d i e s . A

subsequent s e c t i o n i s concerned wi th t h e conclus ions t h a t those

i n v e s t i g a t o r s reached, which a r e n o t n e c e s s a r i l y d i r e c t l y based

upon r e s e a r c h t h a t was accomplished by them.

a. A 7-inch d iameter lamp r e q u i r e s about twice t h e i n t e n -

s i t y of a 5-inch d iameter lamp, of about h a l f t h e a r e a , f o r s i g -

n a l e f f e c t i v e n e s s .

b. I n daytime 52 cp i s p r e f e r r e d f o r t h e t a i l l i g h t and a t

n igh t t ime 7 cp.

c . For two l i g h t s t o be seen a s s e p a r a t e t h e edge-to-edge

s e p a r a t i o n d i s t a n c e should be n o t l e s s than 3.5 inches a t 500

f e e t .

d. A survey of used v e h i c l e s showed t h a t t h e mean s i g n a l

lamp t o t a i l lamp i n t e n s i t y r a t i o was 12.7 t o 1.

e . For s i g n a l lamps i n daytime t h e r e was l i t t l e s u b j e c t i v e

improvement i n e f f e c t i v e n e s s beyond 500 cp.

f . A survey of i n - s e r v i c e v e h i c l e s showed t h a t l i g h t out -

p u t v a r i e d 2 70 p e r c e n t ,

g. I n some v e h i c l e s t a i l lamp v o l t a g e was found t o be

approximately 50 pe rcen t of r a t e d o u t p u t a t engine i d l e speed.

h e I n a s imula t ion a mul t i - co lo r system appeared t o have

t h e lowest r e a c t i o n times t o t h e s i g n a l s .

i, The confusion i n i n t e r p r e t a t i o n of t h e meaning of s i g -

n a l s was g r e a t e s t f o r t h e convent ional system and l e a s t f o r a mul t i - co lo r ( ~ r i - l i g h t ) system,

j . The r e a c t i o n t imes t o s i g n a l s given by t h e convent ional

system were longer than t o a mul t i - co lo r system.

k. There was no d i f f e r e n c e i n t h e c l o s i n g r a t e o r s teady-

s t a t e headway a t t a i n e d by s u b j e c t s i n a two-car "coupling" t a s k

when t h e l e a d c a r showed r e d , amber, o r green t a i l l i g h t s .

1. A system i n which s i g n a l s were given t o a fol lowing-car

d r i v e r , coded on t h e b a s i s of h i s headway and r e l a t i v e v e l o c i t y

wi th r e s p e c t t o t h e l e a d c a r , was b e s t i n reducing headway var-

i ance i n day and n i g h t tests.

m. The T r i - l i g h t systems provided s i g n i f i c a n t l y lower

d e t e c t i o n times of l e a d v e h i c l e c o a s t i n g than t h e convent ional

system,

n. A t ime s e r i e s a n a l y s i s showed t h a t car - fo l lowing phase

l a g s were l e a s t f o r t h e T r i - l i g h t systems.

o. The e f f e c t i v e n e s s of an e a r l y warning ( c o a s t i n g ) s i g -

n a l i s a f u n c t i o n of t h e p r o b a b i l i t y t h a t it w i l l be followed

by a brake s i g n a l .

p. F a l s e - p o s i t i v e braking responses inc reased dur ing t h e

presence of t h e yellow warning s i g n a l a s r ed ( s t o p ) s i g n a l f r e -

quency i n c r e a s e d .

q . A car- fo l lowing s imula t ion sugges ted t h a t v e l o c i t y and

d e c e l e r a t i o n informat ion should be p resen ted t o d r i v e r s .

r , A daytime e v a l u a t i o n of a v e l o c i t y d i s p l a y showed t h a t

such a d i s p l a y provided informat ion which enabled a fo l lowing d r i v e r t o reduce headway v a r i a n c e compared t o t h e convent ional

system.

8

s. The convent ional brake l i g h t s produced g r e a t e r headway

v a r i a n c e than when no s i g n a l s a t a l l were given by t h e l e a d c a r .

t , An occ lus ion of v i s i o n experiment showed t h a t t h e use

of a v e l o c i t y d i s p l a y pe rmi t t ed less a t t e n t i o n t o be pa id t o

l e a d c a r movements by t h e fo l lowing c a r d r i v e r , sugges t ing t h a t

t h e d i s p l a y provided u s e f u l augmenting informat ion .

2. CONCLUSIONS REACHED BY THE PRIOR CONTRACTORS

a . The v a r i a t i o n i n l i g h t o u t p u t should be reduced from

t h e p r e s e n t k 70 pe rcen t t o k 15 pe rcen t on new v e h i c l e s .

b. The pe rmi t t ed i n t e n s i t y range f o r lamps i s t o o l a r g e .

c . Rear l i g h t i n g systems should be operab le whenever t h e

v e h i c l e i s i n motion.

d . E f f e c t i v e v i s i o n r e q u i r e s very high i n t e n s i t i e s of

lamps i n fog.

e. Ten d i s c r e t e s i g n a l s a r e maximum.

f , Closure and headway d i s t a n c e may be adequate ly conta ined

i n a l i g h t i n g a r r a y .

g. Color should be used only secondar i ly .

h. Var iable f l a s h r a t e does n o t appear t o be a p r a c t i c a l

coding dimension.

i. Lamps should be spaced a minimum of 3.5 i n c h e s , edge-

to-edge, t o be seen a s s e p a r a t e a t 500 f e e t .

j . The v e r t i c a l ang le of lamps may be reduced because of

f l a t t e r roads b u t p o s s i b l y t h e h o r i z o n t a l ang le should be

inc reased .

k . A t h r e e l i g h t s t r i n g w i t h supplemental l i g h t s i s requ i red .

1. Improved r e a r l i g h t i n g w i l l show up i n more e f f i c i e n t

t r a f f i c flow and should n o t be judged on t h e b a s i s of a c c i d e n t

r e d u c t i o n because of o t h e r c a u s a l f a c t o r s .

m. Color coding i s e f f e c t i v e .

n. Turn s i g n a l s need n o t be amber b u t should be a d i f f e r -

e n t c o l o r from brake s i g n a l s .

o. Brake l i g h t s should be a d i f f e r e n t c o l o r from d i r e c -

t i o n a l l i g h t s and running l i g h t s .

p. Elevated running l i g h t s should be given s e r i o u s con-

s i d e r a t i o n .

q. The I r e l a n d l i g h t and an overs ized l i c e n s e p l a t e l i g h t

designed t o p rese rve daytime v i s u a l cues should be eva lua ted .

r. React ion time t o s i g n a l s given by t h e conven t iona l sys-

tem is longer than t h a t from a double-red system o r a T r i - l i g h t

system.

s. The s u b j e c t i s a b l e t o use a d d i t i o n a l informat ion pro-

v ided by more s o p h i s t i c a t e d systems.

t. Means should be developed f o r p r e s e n t i n g headway and

r e l a t i v e v e l o c i t y informat ion .

u. The use of a brake warning s i g n a l appears t o be u s e f u l

i n t h a t it can reduce r e a c t i o n times t o t h e s t o p s i g n a l .

v. There appears t o be an optimum (1 s e c ) i n t e r s i g n a l

i n t e r v a l between t h e warning s i g n a l and t h e s t o p s i g n a l .

w. The use of a d i s p l a y which provides v e l o c i t y informa-

t i o n improves car - fo l lowing performance,

x. There was a s i g n i f i c a n t l e a r n i n g e f f e c t f o r s u b j e c t s

fo l lowing t h e c a r showing t h e v e l o c i t y d i s p l a y .

y. Standard s t o p l i g h t s l e d t o p o o r e s t performance i n

car - fo l lowing.

z. A quickening f e a t u r e , based upon v e l o c i t y and a c c e l -

e r a t i o n , may be h e l p f u l i n improving t h e e f f e c t i v e n e s s of a

v e l o c i t y d i s p l a y .

aa . The v e l o c i t y d i s p l a y r e q u i r e d l e s s a t t e n t i o n a l demand

than t h e conven t iona l d i s p l a y and t h e n o - l i g h t s d i s p l a y i n day-

t ime.

bb. A t h e o r e t i c a l ca r - fo l lowing a n a l y s i s showed t h a t t h e

use of v e l o c i t y and a c c e l e r a t i o n informat ion coded i n t h e r e a r

l i g h t i n g system would provide u s e f u l in fo rmat ion .

3 . HSRI INTERPRETATIONS OF THE CONCLUSIONS REACHED BY THE P R I O R CONTRACTORS

The a n a l y s i s of t h e f i n d i n g s anc conclus ions t h a t have been

drawn by t h e f o u r p r i o r c o n t r a c t o r s who c a r r i e d o u t r e sea rch i n

r e a r l i g h t i n g i n t h e p a s t yea r has i n d i c a t e d a number of i tems

i n which t h e r e was, i n g e n e r a l , agreement among them. There

were a h o s t of s p e c i f i c p o i n t s r a i s e d by each of t h e cont rac-

t o r s and i n t h i s review we have tended t o g l o s s over them i n

o r d e r t o reach t h e h i g h l i g h t s and s e e how they may a f f e c t t h e

type of r e s e a r c h program t h a t H S R I was t o conduct. A number of

concepts have emerged q u i t e s t r o n g l y which i n d i c a t e s t e p s t h a t

might be taken t o achieve an improvement i n t h e r e a r l i g h t i n g

system, o r t h a t sugges t a r e a s f o r f u r t h e r r e s e a r c h which should

be given p r i o r i t y because of t h e l i k e l i h o o d t h a t they w i l l l ead

t o f i n d i n g s which can be a p p l i e d t o t h e s e t t i n g of r e a r l i g h t -

i n g system s tandards . The conclus ions t h a t w e f e e l can reason-

a b l y be drawn from t h e aforementioned s t u d i e s a r e a s fo l lows:

a . The redundancy p r i n c i p l e should be used i n t h e coding

of s i g n a l l i g h t s .

b. Red should be rese rved f o r braking only .

c . The c a s e f o r green a s a t a i l l i g h t c o l o r i s s t r o n g .

d. The r e a r l i g h t i n g system should have m u l t i - i n t e n s i t y

c a p a b i l i t y .

e. There should be some r e l a t i v e s t a n d a r d i z a t i o n of t h e

l o c a t i o n s of lamps c a r r y i n g s p e c i f i c f u n c t i o n s .

f . The e a r l y warning l i g h t p r i n c i p l e r e q u i r e s f u r t h e r

i n v e s t i g a t i o n .

g. Veloci ty and d e c e l e r a t i o n informat ion appears t o be

u s e f u l f o r fo l lowing d r i v e r s .

h. A number of u s e f u l techniques a p p l i c a b l e t o r e sea rch

s t u d i e s i n r e a r l i g h t i n g systems have been developed.

4. ACCIDENT DATA

During t h e year 1967 approximately 5200 persons were k i l l e d

i n a c c i d e n t s i n v o l v i n g v e h i c l e s o r i e n t e d i n t h e same d i r e c t i o n

of t r a v e l , which i s about 10 p e r c e n t of a l l t r a f f i c f a t a l i t i e s

and 23 p e r c e n t of a l l such f a t a l i t i e s r e s u l t i n g from two-car

c o l l i s i o n s . The term " o r i e n t e d " i n t h e same d i r e c t i o n r a t h e r

than "moving" i n t h e same d i r e c t i o n i s used because some 2700 of

those 5200 d e a t h s , o r 52 p e r c e n t , occurred i n a c c i d e n t s where

one v e h i c l e was s topped, almost s topped, o r parked.

Of a l l a c c i d e n t s r e p o r t e d l a s t yea r almost 7 m i l l i o n , o r

50 p e r c e n t of t h e t o t a l , involved l i k e - o r i e n t e d v e h i c l e s . Tables

1-3 show t h e breakdown of f a t a l a c c i d e n t s invo lv ing l i k e o r i e n t e d

v e h i c l e s , and Tables 4-6 those invo lv ing a l l types of a c c i d e n t s

f o r l i k e - o r i e n t e d v e h i c l e s .

Table 1 shows t h a t 10 pe rcen t of a l l f a t a l a c c i d e n t s a r e

caused by rear-end c o l l i s i o n s . Also, when only two-car a c c i d e n t s

a r e cons idered t h e rear-end a c c i d e n t s account f o r 23 pe rcen t of

f a t a l a c c i d e n t s . Table 2 shows t h a t f o r two-car a c c i d e n t s

invo lv ing l i k e - o r i e n t e d v e h i c l e s t h e parked v e h i c l e o r t h e one

t h a t i s s topped, s topp ing , o r s t a r t i n g accounts f o r about 53

pe rcen t of a l l f a t a l a c c i d e n t s whi le those a c c i d e n t s occur r ing

when both v e h i c l e s were moving accounted f o r t h e remainder , o r

47 pe rcen t . Table 3 shows t h a t 3350 t a t a l i t i e s occurred i n l i k e -

o r i e n t e d r u r a l d r i v i n g and 1900 i n urban environments. I n t h e s e

a c c i d e n t s 830 were caused by one v e h i c l e c o l l i d i n g wi th a parked

c a r , 1900 when one v e h i c l e c o l l i d e d wi th ano the r which was s top-

ped, s topp ing , o r s t a r t i n g , and t h e remainder , 2430, involved

two moving v e h i c l e s .

When a l l a c c i d e n t s a r e cons idered then it i s seen , i n Table

4 , t h a t l i k e - o r i e n t e d v e h i c l e a c c i d e n t s account f o r 50 p e r c e n t

of t h e t o t a l . Furthermore, l i k e - o r i e n t e d v e h i c l e s account f o r

62 p e r c e n t of a l l two-car a c c i d e n t s wi th approximately an equa l

TABLE 1. PERCENT OF FATAL ACCIDENTS INVOLV- I N G LIKE ORIENTED VEHICLES (1967)

TABLE 2. PERCENT DISTRIBUTION OF FATAL ACCIDENTS FOR LIKE ORIENTED VEHICLES ONLY (1967)

I n t e r s e c t i o n

N o n - I n t e r s e c t i o n

T o t a l

TABLE 3. NUMBER OF FATALITIES I N LIKE ORIENTED VEHICLE ACCIDENTS (1967)

% o f t o t a l

1 , 3

8.5

9.8



T o t a l

% o f r u r a l

1 . 0

8 . 3

9 . 3

One v e h i c l e pa rked

I - 18%

15 .4%

One v e h i c l e s t o p p e d , s t o p p i n g , s t a r t i n g

23%

40%

37.5%

% o f u rban

1 , 8

9 .0

10 .8

Both v e h i c l e s moving

77%

42%

47.1%

Both veh. moving

500

19 30

2430

% r u r a l two car

2 .3

19 .0

21 .3

% t o t a l two car

3 . 1

2 0 . 1

23.2

% u rban two car

4.4

22.2

26.6



T o t a l

One veh. p a r k e d

- 830

8 30

350

3000

3350

650

4600

5250

One veh. s t o p p e d , s t o p p i n g , s t a r t i n g

15 0

1840

1990

Urban

300

16 0 0

1900

TABLE 4. PERCENT OF ALL ACCIDENTS INVOLVING LIKE ORIENTED VEHICLES (1967)

TABLE 5. PERCENT DISTRIBUTION OF ALL ACCIDENTS FOR LIKE ORIENTED VEHICLES ONLY (1967)

TABLE 6 . NUMBER OF LIKE ORIENTED VEHICLE ACCIDENTS (1967)

% rural two car

1 6 . 3

44.5

60 .8



T o t a l

% u r b a n two car

15 .3

49.4

64.7

% o f u r b a n

1 3 . 1

42 .3

55.4

i

Both v e h i c l e s moving

One v e h i c l e p a r k e d

% t o t a l two car

15.6

46.7

62 .3

% o f t o t a l

12.2

37.8

50.0

One v e h i c l e s t o p p e d , s t o p p i n g , s t a r t i n g

% o f r u r a l

9.9

26.5

36.4



T o t a l


on-Intersection T o t a l

Urban

l t28O10O0

4 ,140 ,000

5 ,420 ,000

- 31%

23.4%

T o t a l

1 ,670 ,000

5 ,180 ,000

6 ,850 ,000

One veh . p a r k e d

- 1 ,600 ,000

1 ,600 ,000

R u r a l

3901000

1 ,040 ,000

1 ,430 ,000

47%

44%

45%

53%

25%

31.6%

One veh . s t o p p e d , s t o p p i n g , s t a r t i n g

780,000

2 ,300 ,000

3 ,080 ,000

Both veh. moving

890,000

1 ,300 ,000

2 ,190 ,000 pp --

p r o p o r t i o n o c c u r r i n g i n r u r a l and urban a r e a s . Table 5 i n d i -

c a t e s t h a t , f o r a l l a c c i d e n t s i n v o l v i n g l i k e - o r i e n t e d v e h i c l e s

o n l y , t h e inc idence of a c c i d e n t s i n v o l v i n g a parked v e h i c l e i s i n c r e a s e d t o 23 p e r c e n t whi le t h o s e i n v o l v i n g one v e h i c l e s top-

ped, s topp ing , o r s t a r t i n g i s 45 p e r c e n t , The p ropor t ion involv-

i n g two moving v e h i c l e s i s r e l a t i v e l y lower compared t o t h e f a t a l

a c c i d e n t d a t a a t 31 p e r c e n t . Table 6 shows t h e s t a g g e r i n g num-

b e r of l i k e - o r i e n t e d v e h i c l e a c c i d e n t s .

These d a t a seem t o i n d i c a t e t h a t one o r more of t h e fol low-

i n g v e h i c l e s t a t e s i g n a l s would g r e a t l y improve t h e prognosis

f o r d r i v i n g s a f e t y : (1) a s topped c a r s i g n a l , (2 ) a parked c a r

s i g n a l , ( 3 ) a r a p i d l y d e c e l e r a t i n g v e h i c l e s i g n a l , and ( 4 ) a

v e l o c i t y i n d i c a t o r ,

I n an i n t e n s i v e s tudy on a 41-mile s t r e t c h of freeway nea r

San Antonio, Texas, M i t c h e l l (1966) found t h a t rear-end c o l l i -

s i o n s a lone accounted f o r 60 p e r c e n t of a l l a c c i d e n t s on t h e

freeway proper and 80 p e r c e n t of e n t r a n c e ramp a c c i d e n t s . Such

d a t a a g a i n p o i n t t o t h e need f o r v e l o c i t y o r d e c e l e r a t i o n i n f o r -

mation. An e x t e n s i v e Bureau of P u b l i c Roads s tudy (Solomon,

1964) found t h a t 46 p e r c e n t of a l l daytime a c c i d e n t s and 40

p e r c e n t of a l l n i g h t a c c i d e n t s were two-car rear-end c o l l i s i o n

t y p e s on t h e 800 m i l e s of main r u r a l highway inc luded i n t h e

s tudy . The s tudy showed t h a t 47 p e r c e n t of two-car rear-end

c o l l i s i o n s involved c a r s t r a v e l i n g a t a speed d i f f e r e n c e of

g r e a t e r than 20 mph, whereas i n normal highway t r a f f i c on ly 7

p e r c e n t of v e h i c l e s t r a v e l e d a t such d i f f e r e n t i a l speeds. Also,

whereas over 99 p e r c e n t of v e h i c l e p a i r s i n t h e normal t r a f f i c

t r a v e l e d a t speed d i f f e r e n t i a l s of less than 30 mph, 32 p e r c e n t

of a c c i d e n t involved p a i r s were t r a v e l i n g a t d i s c r e p a n c i e s

g r e a t e r than 30 mph, Another s tudy (Byington, 1963) was con-

cerned wi th a c c i d e n t s on t h e i n t e r s t a t e system. The r e s u l t s

showed t h a t rear-end a c c i d e n t s accounted f o r n e a r l y a l l two-car

c o l l i s i o n s . A s t u d y by V e c e l l i o (1967) concernedwith t r u c k a c c i -

d e n t s on t h e Ohio Turnpike d u r i n g t h e y e a r s 1960-1965 found

t h a t rear -end c o l l i s i o n s occur red a s fo l lows: 66 p e r c e n t on

t h e l e v e l , 28 p e r c e n t on t h e up g rade , 5 p e r c e n t on t h e down

grade and 1 p e r c e n t on a h i l l c r e s t . These d a t a c l e a r l y i n d i -

c a t e , by t h e s h a r p d i f f e r e n c e i n rear-end a c c i d e n t exper ience

between down grade and up grade f o r t r u c k s , t h a t speed d i f f e r -

e n t i a l s a r e n o t r e a d i l y pe rce ived by t h e d r i v e r s of o t h e r vehi -

cles whose speed i s n o t a f f e c t e d s i g n i f i c a n t l y by t h e grade.

5 . CONCLUSIONS BASED UPON TRAFFIC ACCIDENT ANALYSIS

The d a t a a n a l y s i s concerned wi th t r a f f i c a c c i d e n t s t a t i s -

t i c s h a s . s u g g e s t e d some c l e a r i m p l i c a t i o n s f o r r e a r s i g n a l

system des ign. Although t h e accuracy of t r a f f i c a c c i d e n t s t a t i s -

t i c s may be ques t ioned t h e r e can be l i t t l e doubt t h a t t h e ve ry

l a r g e numbers t h a t a r e involved c l e a r l y i m p l i c a t e t h e rear-end

a c c i d e n t phenomenon a s one of t h e major c o s t s i n t r a f f i c a c c i -

d e n t s . This i s t r u e f o r a l l c a t e g o r i e s of a c c i d e n t s i n c l u d i n g

f a t a l a c c i d e n t s , b o d i l y i n j u r y , o r j u s t p r o p e r t y damage. The

a n a l y s i s seems t o i n d i c a t e t h a t s i g n a l s t h a t show a fo l lowing

d r i v e r whether a v e h i c l e ahead of him i s stopped o r moving,

whether it i s moving forwards o r backwards, t h e v e l o c i t y wi th

which it i s moving and t h e magnitude a t which it may be d e c e l e r -

a t i n g would be u s e f u l in fo rmat ion . I n summary, t h e n , t h e d a t a

t e n d t o i n d i c a t e t h a t t h e fo l lowing s i g n a l s should be g iven con-

s i d e r a t i o n i n r e a r l i g h t i n g system des ign: (1) parked c a r s i g -

n a l , ( 2 ) s topped c a r s i g n a l , ( 3 ) s t o p p i n g s i g n a l , ( 4 ) r a p i d l y

d e c e l e r a t i n g v e h i c l e s i g n a l , (5 ) v e l o c i t y i n d i c a t o r .

6 . GENERAL CONCLUSIONS

Some g e n e r a l conc lus ions can be a r r i v e d a t based upon t h e

f i n d i n g s of t h e r e s e a r c h s t u d i e s c a r r i e d o u t by o t h e r NHSB con-

t r a c t o r s and from t h e a c c i d e n t d a t a of t h e type t h a t w e have

c i t e d . I t was i n t e r e s t i n g t o n o t e , i n c i d e n t a l l y , t h a t none of

t h e p rev ious c o n t r a c t o r s made r e f e r e n c e t o a c c i d e n t s t a t i s t i c s

i n t h e i r r e p o r t s . I t i s our b e l i e f t h a t t h e r e i s a cons iderable

amount of informat ion i n such d a t a , a s we have a l ready suggested,

Nonetheless , t h e r e i s c l e a r l y some over lap between t h e conclu-

s i o n s reached from t h e acc iden t d a t a and those t h a t were reason-

a b l e t o conclude from t h e p r i o r c o n t r a c t o r s ' r e p o r t s (Sect ion 3 ) .

One genera l conclusion would be t h a t b e t t e r information i s

requ i red t o i n d i c a t e t h a t a l ead ing v e h i c l e i s d e c e l e r a t i n g .

This may be done by improving t h e d e t e c t a b i l i t y of t h e s t o p s i g -

n a l on v e h i c l e s . Another p r i n c i p l e i s t o p r e s e n t d e c e l e r a t i o n

information. The e a r l y warning l i g h t which was proposed may

provide u s e f u l informat ion t o reduce rear-end acc iden t s occur r ing

i n s p e c i f i c s i t u a t i o n s such a s t h e en t rance ramps t o freeways,

expressways, and i n t e r s t a t e roads. Qui te c l e a r l y a v e l o c i t y

d i s p l a y i s a l s o d e s i r a b l e based on t h e o v e r a l l f ind ings . F i n a l l y ,

while v i r t u a l l y neglec ted i n t h e p r i o r c o n t r a c t o r s ' r e p o r t s , the

parked c a r appears t o pose a p a r t i c u l a r hazard which may be par-

t i a l l y removed by an improvement i n t h e r e a r l i g h t i n g d i sp lay .

7 . P R I O R I T Y ORDERING OF RESEARCH TASKS

The p r i o r i t y o rde r ing t h a t we a r e proposing i s based upon

t h e ana lyses c a r r i e d o u t i n t h e foregoing s e c t i o n s and t akes

i n t o account t h e needs of t h e NHSB a s o u t l i n e d t o us i n d i scus -

s i o n s with t h e c o n t r a c t monitor and o t h e r members of NHSB s t a f f .

These d i s c u s s i o n s had i n d i c a t e d t o us t h a t NHSB requ i red addi-

t i o n a l d a t a by t h e end of t h e c o n t r a c t period which would enable

them t o prepare a r e v i s e d v e h i c l e r e a r l i g h t i n g s t andard incor-

pora t ing recommendations l ead ing t o a more e f f e c t i v e system.

I t was our b e l i e f t h a t i n t h e remaining per iod of t h i s c o n t r a c t

it would be p o s s i b l e t o produce necessary information t o permit

a s t andard t o be prepared which would l ead t o an upgrading i n

t h e e f f e c t i v e n e s s of r e a r l i g h t i n g s i g n a l systems. Such a

s t andard would be termed t o be i n t e r i m i n na tu re . This is t o

say , i t was be l i eved t h a t an improvement i n t h e r e a r l i g h t i n g

system could be s p e c i f i e d w i t h i n t h e time frame of t h e p r o j e c t ;

b u t t h e improvement would n o t be such t h a t it would be appro-

p r i a t e t o say t h a t t h e system t h a t may be recommended was opt imal .

To achieve n e a r l y opt imal r e a r l i g h t i n g c o n f i g u r a t i o n s w i t h i n t h e

p r e s e n t s t a t e - o f - t h e - a r t , which invo lves s i g n a l l i g h t s t o t r a n s -

m i t i n fo rmat ion and p rec ludes t h e use of e lec t ro-mechanica l sens-

i n g d e v i c e s , w i l l r e q u i r e f u r t h e r r e s e a r c h e f f o r t .

I t should be noted t h a t i f an i n t e r i m recommendation i s

made l e a d i n g t o a more e f f e c t i v e system, then it i s probable

t h a t subsequent r e s e a r c h may show t h a t t h e system i s n o t t h e

most d e s i r a b l e one, There fo re , i f a f u r t h e r change i s l a t e r

i n d i c a t e d f o r a more n e a r l y opt imal system, t h e l a t t e r w i l l have

t o be made t o be compatible n o t on ly wi th t h e convent ional sys-

tem found on v e h i c l e s today, b u t t h e i n t e r i m system t h a t may be

proposed a s a r e s u l t of t h e s t u d i e s t h a t w i l l be c a r r i e d o u t i n

t h i s p r o j e c t and p rev ious work. This d u a l c o m p a t i b i l i t y problem

t h a t may be r a i s e d i s one t h a t w i l l have t o be given s e r i o u s con-

s i d e r a t i o n i n t h e recommendations t h a t emanate f o r an i n t e r i m

s p e c i f i c a t i o n . The s t u d i e s t o be proposed, which a r e i n d i c a t e d

i n t h e p r i o r i t y o r d e r i n g t h a t i s p resen ted i n t h i s s e c t i o n , w i l l

r e f l e c t t h e immediate need t o provide d a t a l e a d i n g t o i n t e r i m

r e a r l i g h t i n g system s t a n d a r d s and a l s o bea r i n mind t h e longer-

term need f o r cont inued r e s e a r c h i n o r d e r t o develop a more o p t i -

mal c o n f i g u r a t i o n .

7.1 TASK PRIORITY ORDERING.

1. Eva lua t ion of coding dimensions and f u n c t i o n a l

s e p a r a t i o n of lamps.

2 . Determinat ion of maximum and minimum v a l u e s f o r

m u l t i - i n t e n s i t y l i g h t i n g requi rements f o r t a i l

and s i g n a l lamps.

3 . Human eng inee r ing s tudy t o de termine d r i v e r

swi tch ing and feedback mode requi rements f o r

m u l t i - i n t e n s i t y l i g h t i n g .

4. Evaluat ion of t a i l l i g h t c o l o r .

5. Turn s i g n a l v i s i b i l i t y requirements .

6 . Appl ica t ion of s i g n a l system performance measures

t o p r e d i c t a c c i d e n t p r o b a b i l i t y .

7. Evaluat ion of c l o s u r e d e t e c t i o n a s a f f e c t e d by

lamp a r r a y .

8. Evaluat ion of t h e c o a s t i n g ( e a r l y warning) s i g n a l .

9 . Evaluat ion of t h e e f f e c t of s i g n a l l i g h t and t a i l -

l i g h t l o c a t i o n t o provide advance s i g n a l informa-

t i o n .

10. Evaluat ion of a v e l o c i t y d i s p l a y .

11. Analys is of d e c e l e r a t i o n magnitude s i g n a l .

1 2 . Analysis of t u r n s i g n a l c a n c e l l i n g requirements .

13. Development of recommendations f o r an i n t e r i m r e a r

l i g h t i n g system s tandard .

8. ACTUAL TASKS TO BE ACCOMPLISHED

The t a s k s t h a t have been o u t l i n e d i n t h e preceding s e c t i o n

were those t h a t , having been ordered according t o our pe rcep t ion

of t h e i r p r i o r i t y , i t would be d e s i r a b l e t o c a r r y ou t . However,

it was n o t p o s s i b l e t o accomplish a l l of t h e s e goa l s wi th in

t h e funding and time framework of t h i s program. For t h i s reason

a subsec t ion of t h e s e t a s k s were s e l e c t e d , c o n s i s t i n g of Tasks 1 -8 ,

t o comprise t h e resea rch program t o be undertaken.

PART METHOD--RESEARCH TASKS 1. EVALUATION OF CODING DIMENSIONS AND FUNCTIONAL SEPARATION

OF LAMPS (TASK 1)

INTRODUCTION. These s t u d i e s a r e concerned w i t h methods of

coding t h e p r i n c i p a l s i g n a l s g iven by c u r r e n t r e a r l i g h t i n g and

s i g n a l i n g sys tems, namely presence , b rak ing , and t u r n i n g . Pre-

v ious s t u d i e s c a r r i e d o u t s t a t i c a l l y (Mortimer, 1969a) and i n

a c t u a l d r i v i n g on c i t y streets and an expressway (Mortimer, 1969b)

have shown t h a t t h e use of codes o t h e r than i n t e n s i t y and f l a s h ,

which a r e used a t t h e p r e s e n t t ime t o i n d i c a t e b rak ing and t u r n -

i n g s i g n a l s , can enhance d r i v e r performance i n p e r c e i v i n g t h e

s i g n a l s . These s t u d i e s have used l a r g e i n t e n s i t y r a t i o s ( 2 0 : l )

combined w i t h low a b s o l u t e i n t e n s i t i e s (Mortimer, 1969a) i n t h e

s t a t i c t es t , s m a l l e r i n t e n s i t y r a t i o s of 5 : l between s i g n a l and

presence l i g h t s , and somewhat h i g h e r presence l i g h t i n t e n s i t i e s

(Mortimer, 1969b).

The proposed s t u d i e s were concerned wi th t h e hypo thes i s t h a t

g iven a l a r g e i n t e n s i t y r a t i o and h igh a b s o l u t e i n t e n s i t i e s s i m i l a r

t o t h o s e now i n use and l a r g e i n t e n s i t y r a t i o s combined wi th lower

a b s o l u t e i n t e n s i t y l e v e l s somewhat below t h o s e now i n u s e , t h e

e f f i c a c y of t h e coding t echn iques may d i sappear .

I n t h e p r e s e n t s t u d i e s t h e use of number, c o l o r , i n t e n s i t y ,

and f l a s h cues were e v a l u a t e d , i n con junc t ion w i t h v a r i o u s t y p e s

of f u n c t i o n a l s e p a r a t i o n of lamps. Some of t h e same s i g n a l sys -

tems t h a t were used i n a p r i o r dynamic e v a l u a t i o n were used i n

t h e s e t e s t s . Th i s was done s o comparisons could be made w i t h t h e

e a r l i e r dynamic s tudy (Mortimer, 1969b) t o show t h e e f f e c t of

changes i n i n t e n s i t y r a t i o and a b s o l u t e i n t e n s i t y l e v e l s .

I n t h e p rev ious dynamic s tudy presence l i g h t i n t e n s i t y was

7 cp , and s i g n a l l i g h t i n t e n s i t y was 35 cp , g i v i n g an i n t e n s i t y

r a t i o of 5 : l .

METHOD. The procedure used i n these s t u d i e s was the same

a s t h a t which was repor ted i n an e a r l i e r i nves t iga t ion (Mortimer,

1969b). I n b r i e f , two veh ic l e s were used i n these t e s t s which

followed each o the r a t normal d i s t ances while t he c a r s were t r a v e l -

i ng i n the mix of o the r t r a f f i c on Ann Arbor s t r e e t s .

THE LEAD CAR. The lead ca r had s i x a u x i l l i a r y , s p e c i a l lamps

mounted on a b racke t which replaced t h e r e a r bumper. The lamps

were dua l f i l ament , 4-inch diameter, s ea l ed beam u n i t s and were

c a r r i e d i n housings which f a c i l i t a t e d changing n e u t r a l dens i ty

and co lo r f i l t e r s (Figure 1.1). The lamps could be switched i n

and t h e i r funct ion va r i ed by a con t ro l system which was on the

f r o n t , passenger s e a t . I n add i t i on , t h e c a l i b r a t i o n system f o r

maintaining vo l tage t o these lamps and t h e con t ro l box f o r making

minor adjustments t o the vo l tage i n order t o maintain a known

l i g h t output a t the lamps was a l s o on the f r o n t s e a t of t he veh ic le .

A l l s i g n a l s , such a s s t o p and tu rn s i g n a l s , were i n i t i a t e d from a

s p e c i a l c o n t r o l box and no t through the normal brake o r t u rn s i g -

n a l c o n t r o l of t h e veh ic l e , The c o n t r o l and c a l i b r a t i o n systems

i n the lead c a r a r e shown i n Figure 1 . 2 , When s i g n a l s were i n i -

t i a t e d i n t h e lead c a r a s i g n a l was t ransmi t ted t o t he following

c a r which a t t h a t time s t a r t e d r eac t ion time counters i n t h a t

veh ic l e , one counter f o r each sub jec t . The system i s shown i n

Figure 1.3.

THE FOLLOWING CAR. The following c a r was dr iven by one sub-

j e c t and another s u b j e c t s a t i n t he f r o n t , passenger s e a t . Moun-

t e d on t h e hood of t h a t veh ic l e (Figure 1 . 4 ) were two small l i g h t s

which were lit one a t a time a t an average r a t e of t en times per

minute, wi th v a r i a b l e i n t e r - l i g h t i n t e r v a l s . A l i g h t would remain

on e i t h e r u n t i l both s u b j e c t s had responded t o it o r f o r a maxi-

mum of four seconds.

Two switches were placed on the dash s o t h a t they were e a s i l y

operated by t h e d r i v e r when h i s hands were a t t he ten- and two-

oclock pos i t i ons on the s t e e r i n g wheel. These switches were used

Figure 1.1. The t e s t lamps, showing c o l o r f i l t e r and n e u t r a l f i l t e r .

F i g u r e 1 . 2 . C a l i b r a t i a n and c o n t r o l i n s t r u m e n t a t i o n i n l e a d c a r .

------ I D r i v e r Passenqer

Response Time

Hood Mounted

Car Rear Lamps I Task L i g h t s

Lead Car I Following Car ,,-,-'-,,,, F i g u r e 1 . 3 . Lead c a r and f o l l o w i n g c a r l i g h t i n g

system c o n t r o l , s u b j e c t r e s p o n s e and d a t a r e c o r d i n g i n s t r u m e n t a t i o n b lock diagram.

Figure 1 . 4 . The p a r t - t a s k l i g h t s on t h e hood of t h e fo l lbwing c a r and t h e t e s t lamp a r rangement on t h e l ead c a r .

by him t o respond t o t h e hood-mounted l i g h t s . A f o o t swi tch was

l o c a t e d such t h a t t h e d r i v e r could rest h i s l e f t f o o t on it com-

f o r t a b l y whi le d r i v i n g and he depressed it a s soon a s he d e t e c t e d

s i g n a l s given by t h e l e a d c a r .

The passenger h e l d a swi tch box con ta in ing f o u r swi tches .

Two swi tches a t t h e lower l e f t co rne r were f o r use by t h e l e f t

thumb f o r responses t o t h e hood-mounted l i g h t s , one swi tch f o r

t h e l e f t and r i g h t l i g h t r e s p e c t i v e l y . The swi tches i n t h e r i g h t

co rne r were f o r o p e r a t i o n by t h e r i g h t thumb and were t o i n d i c a t e

t h e type of s i g n a l , s t o p o r t u r n , t h a t t h e s u b j e c t had d e t e c t e d

on t h e l e a d c a r .

Recording Equipment. An experimenter s a t i n t h e r e a r s e a t

of t h e fo l lowing c a r and monitored t h e record ing equipment which

c o n s i s t e d of two d i g i t a l c locks read ing t o 1/1000 seconds. I n t e r -

c a r communication was provided by means of CB t r a n s m i t t e r -

r e c e i v e r s . F igure 1 .5 shows t h e equipment l a y o u t i n t h e fol low-

i n g c a r .

L igh t ing Systems. Five l i g h t i n g systems were compared i n

t h e s e tests, These systems were t h e same a s f i v e of t h e e i g h t

t h a t have been used i n a previous s tudy (Mortimer, 1969b) . I n

o r d e r t o f a c i l i t a t e a comparison wi th t h a t s tudy t h e system num-

b e r s t h a t were used then a r e r e t a i n e d h e r e , Systems 1, 3 , 4 , 6 ,

and 8 of t h e previous s tudy were used i n t h e s e tests. The des-

c r i p t i o n of t h e s e systems i s a s fol lows:

1. (1) presence , s t o p , and t u r n i n one lamp ( a l l r ed )

2 . ( 3 ) presence and t u r n i n one lamp, s t o p i n a s e p a r a t e

lamp ( a l l r e d )

3. ( 4 ) presence , s t o p , and t u r n i n t h r e e s e p a r a t e lamps

( a l l r e d )

4 . ( 6 ) presence and t u r n i n one lamp (green) ; s t o p i n a

s e p a r a t e lamp ( r e d )

5. ( 8 ) presence (green) ; t u r n (amber) ; s t o p ( r e d ) , a l l

i n s e p a r a t e lamps.

F i g u r e 1 . 5 . The a r rangement i n t h e f o l l o w i n g c a r , showing s u b j e c t s ' r e s p o n s e s w i t c h e s and d a t a r e c o r d i n g equipment .

I n each system presence l i g h t s remained on a t a l l times. These

l i g h t i n g c o n f i g u r a t i o n s a r e shown i n F igure 1 .6 .

The Dependent Var iab le . The r e a c t i o n time of each s u b j e c t

t o t h e s t o p and t u r n s i g n a l s was measured t o t h e n e a r e s t 0.001

seconds,

S i g n a l Modes. The r e a c t i o n times t o f o u r s i g n a l s were mea-

sured:

1. (1) t u r n s i g n a l , l e f t o r r i g h t

2. ( 2 ) s t o p s i g n a l

3 . ( 3 ) t u r n - s t o p s i g n a l ( s t o p s i g n a l , when a p r e v i o u s l y

i n i t i a t e d t u r n s i g n a l was s t i l l f l a s h i n g )

4 . ( 4 ) s t o p - t u r n s i g n a l ( t u r n s i g n a l , when a p r e v i o u s l y

i n i t i a t e d s t o p s i g n a l was s t i l l be ing shown).

Turn S i g n a l F lash Rate. Turn s i g n a l s were o f a conven t iona l

f l a s h i n g t y p e , wi th a f l a s h r a t e of 1 cps and 75 p e r c e n t "on" time.

Photometry. L igh t i n t e n s i t i e s f o r s i g n a l and presence l i g h t s

were c o n t r o l l e d p r i n c i p a l l y by t h e use of n e u t r a l d e n s i t y f i l t e r s ,

and minor adjus tments were c a r r i e d o u t by means of po ten t iomete r s .

S i g n a l l i g h t v o l t a g e s were between 1 2 and 12.5 v o l t s .

A S p e c t r a - P r i t c h a r d photometer which had been c r o s s - c a l i b r a t e d

a g a i n s t a Macbeth I l luminometer was used t o measure i n t e n s i t i e s .

PROCEDURE. The s u b j e c t s , s e a t e d i n t h e f r o n t s e a t of t h e f o l -

lowing c a r , were randomly ass igned t o d r i v e r and passenger pos i -

t i o n s which t h e y kep t throughout t h e t e s t . The d r i v e r was t o l d t o

ma in ta in a normal, s a f e d i s t a n c e behind t h e l e a d c a r . S u b j e c t s

were i n s t r u c t e d t o respond a s r a p i d l y a s p o s s i b l e t o t h e hood-

mounted l i g h t s , and t o t h e l e a d c a r ' s s t o p and t u r n s i g n a l s .

They were given both s t a t i c and dynamic p r a c t i c e wi th system 1,

which was taken t o be r e p r e s e n t a t i v e of t h e mode of o p e r a t i o n of

t h e r e a r l i g h t i n g system c u r r e n t l y used i n t h e United S t a t e s .

When t h e s u b j e c t s were acqua in ted wi th t h e o p e r a t i o n of t h e sys-

t e m and f a m i l i a r w i t h t h e t a s k , they were shown t h e presence l i g h t s ,

s t o p s i g n a l , and t u r n s i g n a l of t h e system t h a t had been randomly

Figure 1 . 6 . The l i g h t i n g c o n f i g u r a t i o n s . P = Presence ( t a i l l i g h t ) , S = Stop, T = Turn, R = Red, A = Amber, G = Green-blue.

s e l e c t e d from t h e f i v e systems a s t h e f i r s t wi th which they

would work.

The t e s t was then begun by running t h e v e h i c l e s on Stadium

Boulevard and Washtenaw Avenue i n t h e c i t y of Ann Arbor. The

f i r s t l i g h t i n g system t o be e v a l u a t e d was run u n t i l 1 6 r e a c t i o n

times, f o u r i n each s i g n a l mode, had been obta ined. The s i g n a l

modes were randomly o rde red i n each l i g h t i n g system f o r each p a i r

of s u b j e c t s . When t h e t e s t i n g of each s u b j e c t had been com-

p l e t e d , t h e s u b j e c t s made a r a t i n g us ing a t en -po in t s c a l e of

t h e " e f f e c t i v e n e s s i n g i v i n g s i g n a l s " of t h e system t h a t had j u s t

been used.

The presence and s i g n a l l i g h t s of t h e n e x t randomly selec-

t e d system were then demonstrated and t h e procedure r e p e a t e d

u n t i l t h e d a t a had been c o l l e c t e d f o r a l l f i v e systems. T o t a l

t e s t i n g time was about two and one h a l f hours f o r each group of

s u b j e c t s . A rest p e r i o d was given a t t h e halfway mark.

Tests were only conducted on weekday n i g h t s under c l e a r

weather c o n d i t i o n s . The r o u t e s e l e c t e d f o r t h e test ensured

t h a t t h e s u b j e c t would encounter a v i s u a l background of s t o r e -

f r o n t i l l u m i n a t i o n , t r a f f i c s i g n a l s , s t r e e t l i g h t i n g , neon s i g n s ,

and a f a i r l y h igh d e n s i t y of o t h e r t r a f f i c , Each p a i r of sub-

j e c t s completed about 30 mi les of c i t y d r i v i n g .

THE EFFECTS OF H I G H INTENSITY, H I G H RATIO. I n t h e f i r s t

experiment t h e procedure used was a s i n d i c a t e d above. The major

d i f f e r e n c e between t h i s experiment and t h e one conducted e a r l i e r

(Mortimer, 1969b) us ing some of t h e same systems is t h a t a

g r e a t e r a b s o l u t e i n t e n s i t y v a l u e f o r t h e s i g n a l l i g h t was used,

which a l s o produced a h i g h e r s igna l -p resence l i g h t r a t i o . I n

t h i s test s i g n a l l i g h t i n t e n s i t y was 91 cp and presence l i g h t

i n t e n s i t y was 7 cp , g i v i n g an i n t e n s i t y r a t i o of 13 : l .

A t o t a l of 4 0 s u b j e c t s was used i n t h i s t es t , 13 females

and 2 7 males between t h e ages of 18 and 28 yea r s . S u b j e c t s were

t e s t e d f o r c o l o r v i s i a n d e f i c i e n c i e s and on ly t h o s e who were nor-

mal were used. 30

THE EFFECTS OF LOW INTENSITY, HIGH RATIO. I n t h i s t e s t t h e

i n t e n s i t y r a t i o between s i g n a l and presence s i g n a l l i g h t s was

t h e same a s i n t h e f i r s t experiment ( 1 3 : l ) b u t t h e a b s o l u t e

i n t e n s i t y of t h e s i g n a l was decreased t o 35 cp and t h e presence

l i g h t i n t e n s i t y was 2 . 7 cp. There fo re , t h i s r e p r e s e n t e d a l i g h t -

i n g c o n f i g u r a t i o n which would be somewhat below t h e SAE recom-

mended minimum s i g n a l l i g h t i n t e n s i t y f o r c l a s s B lamps, and

might a l s o s i m u l a t e a c o n d i t i o n i n which t h e t r ansmiss ion char-

a c t e r i s t i c s of t h e l e n s had been a l t e r e d o r d i r t was p r e s e n t on

t h e o u t s i d e of t h e lamp t o reduce l i g h t t r ansmiss ion .

For ty s u b j e c t s were a l s o used i n t h i s tes t c o n s i s t i n g of

11 females and 29 males between t h e ages of 18 and 36 yea r s .

RESULTS. The a n a l y s i s f o r both experiments was combined

and the reby could show t h e e f f e c t of t h e d i f f e r e n c e s i n a b s o l u t e

i n t e n s i t i e s t h a t were used.

~ e a c t i o n ~ i m e , The r e a c t i o n t ime d a t a were t ransformed t o

loge i n o r d e r t o s a t i s f y t h e normal i ty and homogeneity of v a r i -

ance assumptions of pa ramet r i c t e s t s . Table 1.1 shows t h e sum-

mary of t h e a n a l y s i s of v a r i a n c e of t h e t ransformed r e a c t i o n time

d a t a . I n t h i s a n a l y s i s a l l t h e e f f e c t s invo lv ing t r i a l s were

pooled t o form t h e w i t h i n c e l l s term. The a n a l y s i s of v a r i a n c e

shows t h a t t h e e f f e c t s a t t r i b u t a b l e t o t h e t a s k , which were

d i f f e r e n t f o r t h e d r i v e r and passenger , t h e system used t o g i v e

t h e s i g n a l s , t h e s i g n a l mode, t h e mode x t a s k i n t e r a c t i o n and

t h e system x mode i n t e r a c t i o n . The e f f e c t s were s i g n i f i c a n t

a t 0 . 0 1 l e v e l o r less.

Table 1 . 2 shows t h e geometr ic mean r e a c t i o n t imes f o r t h e

main e f f e c t s of sys tems, t a s k , s i g n a l mode, and i n t e n s i t y ,

Table 1 . 2 shows t h a t t h e t a s k c a r r i e d o u t by t h e d r i v e r

r e s u l t e d i n s h o r t e r r e a c t i o n times than those achieved by passen-

g e r s . This may have been because passengers were c a r r y i n g o u t

a s i g n a l i d e n t i f i c a t i o n t a s k whereas d r i v e r s were c a r r y i n g o u t

a s imple r e a c t i o n time t a s k . On t h e o t h e r hand d r i v e r s were con-

TABLE 1.1. ANALYSIS OF VARIANCE OF REACTION TIME TO SIGNALS. DATA FOR 80 SUBJECTS I N 1/1000 SECONDS TRANSFORMED TO LOG,

BETWEEN GROUPS

Task

I n t e n s i t y

Task x I n t e n s i t y

S u b j e c t Within Groups

WITHIN GROUPS

System 46.0251 4 11,50628 54.800"

System x Task 0.4799 4 0.11998 - System x I n t e n s i t y 1.0199 4 0.25498 1.214

System x Task x I n t e n s i t y 0.6500 4 0.16249 - System x S u b j e c t Within Group 63.8316 304 0,20997 1,721*

Mode 114,3798 3 38.12660 239.549*

Mode x Task 8.1588 3 2.71961 17,087*

Mode x I n t e n s i t y 1,6664 3 0.55546 3.490

Mode x Task x I n t e n s i t y 0.1512 3 0.05040 - Mode x S u b j e c t Within Group 36.2881 228 0.15916 1.305*

System x Mode 67.9945 12 5.66621 44.507*

System x Mode x Task 1.2291 12 0.10243 - System x Mode x I n t e n s i t y 2,3276 12 0.19396 1.524

System x Mode x Task x I n t e n s i t y 0,6308 12 0.5257 - System x Mode x S u b j e c t Wi th in Group 116.1106 912 0,12731 1.044

W I T H I N CELLS 585.5857 4800 0.12200 -

TOTAL 1271.6950 6399

4 S i g n i f i c a n t a t P 5 001,

I

TABLE 1.2, GEOMETRIC MEAN REACTION TIME FOR MAIN EFFECTS

Modes

Turn

Stop

Turn-Stop

Stop-Turn

Systems

1

3

4

6

8

Task - Driver

Passenger

Intensity of Signal

High (91 cp)

Low (35 cp)

Geometric Mean R.T, (seconds)

1.087

.918

.874

1.222

t r o l l i n g t h e v e h i c l e i n a d d i t i o n t o responding t o s i g n a l s .

The h igher s i g n a l i n t e n s i t y r e s u l t e d i n s h o r t e r mean reac-

t i o n times than t h e low s i g n a l i n t e n s i t y .

Dif ferences between s i g n a l modes showed t h a t r e a c t i o n time

t o t h e t u r n s i g n a l when preceded by a s t o p s i g n a l was l o n g e s t ,

followed by r e a c t i o n time t o t h e t u r n s i g n a l a lone , followed by

r e a c t i o n time t o t h e s t o p s i g n a l which was somewhat longer than

t o t h e tu rn - s top cond i t ion .

Dif ferences i n r e a c t i o n time f o r t h e f i v e systems a r e a l s o

shown i n Table 1 . 2 . System 1 had t h e l o n g e s t mean r e a c t i o n t ime,

wi th r e a c t i o n t imes be ing reduced a s f u n c t i o n a l s e p a r a t i o n was

inc reased w i t h i n t h e a l l - r e d systems, and f u r t h e r decreased a s

c o l o r coding and f u n c t i o n a l s e p a r a t i o n a r e in t roduced a s shown

by response times t o systems 6 and 8.

The most important informat ion revea led by t h i s s tudy i s

found by examining t h e s i g n i f i c a n t s i g n a l mode x system i n t e r -

a c t i o n ; t h e geometr ic c e l l means a r e shown i n Table 1.3. Table

1 .3 a l s o shows t h e r e s u l t s of Newman-Keuls tests between systems

i n each s i g n a l mode. I t w i l l be seen t h a t i n t h e t u r n mode

r e a c t i o n t imes t o system 8 were less than those t o a l l o t h e r

systems. I n t h e s t o p mode r e a c t i o n time t o system 8 was less

than t o system 3 . I n t h e tu rn - s top mode r e a c t i o n t i m e t o sys-

tems 8 and 6 were s i g n i f i c a n t l y less than t h e o t h e r systems.

Also, r e a c t i o n time t o system 3 was s i g n i f i c a n t l y l e s s than t o

1 and 4 . I n t h e s top- tu rn mode r e a c t i o n time t o system 8 was

s i g n i f i c a n t l y less than a l l o t h e r s , and systems 4 and 6 had

lower r e a c t i o n times than 3 and 1, whi le 3 was s i g n i f i c a n t l y

less than 1.

Table 1 . 4 shows t h e geometr ic c e l l means f o r t h e s i g n i f i -

c a n t t a s k x mode i n t e r a c t i o n which shows t h a t i n t h e turn-s top

and s top- tu rn modes d i f f e r e n c e s between t h e d r i v e r and passen-

g e r response t imes a r e r e l a t i v e l y reduced compared t o t h e t u r n

and s t o p modes. This would be expected because i n t h e dua l mode

TABLE 1.3. GEOMETRIC MEAN REACTION TIME (SECONDS) FOR EACH SYSTEM AND SIGNAL MODE I N THE H I G H AND LOW INTENSITY CITY D R I V I N G TESTS, FOR 80 SUBJECTS

MODE

SYSTEM

1 3 4 6 8

Turn 1.080 1.160 1 ,102 1.090 1 .011

S t o p 0.917 0 ,951 0.933 0.905 0.891

Turn-Stop 0.985 0.865 0.915 0.812 0.811

S top-Turn 1 .941 1 ,305 1.032 1.086 0.965

I n d i v i d u a l Comparisons by Newman-Keuls T e s t s :

1. Turn: 8 s i g n i f i c a n t l y 1 b e t t e r t h a n 6 , 4 , 3 , 1

2. S top: 8 s i g n i f i c a n t l y b e t t e r t h a n 3

3. Turn-Stop: 8 , 6 , 3 s i g n i f i c a n t l y b e t t e r t h a n 4, 1

8 , 6 s i g n i f i c a n t l y b e t t e r t h a n 3

4. Stop-Turn: 8 , 6 , 4 , 3 s i g n i f i c a n t l y b e t t e r t h a n 1

8 s i g n i f i c a n t l y b e t t e r t h a n 6 , 4 , 3

6 , 4 s i g n i f i c a n t l y b e t t e r t h a n 3

TABLE 1.4. GEOMETRIC MEAN REACTION TIME AS A FUNCTION OF TASK AND MODE

DATA ARE I N SECONDS

Task Turn S t o p Turn-Stop Stop-Turn

D r i v e r 937 .808 ,803 1.154

Passenge r 1 .263 1,044 ,954 1.296

s i t u a t i o n the passenger, having responded t o the f i r s t s i g n a l ,

no longer has a choice r eac t ion time t o ca r ry o u t on t h e appear-

ance of t he second s i g n a l because he need n o t process any in fo r -

mation f o r t h e i d e n t i f i c a t i o n of t he second s i g n a l ,

S igna l I d e n t i f i c a t i o n Er rors . The e r r o r s made by t h e pas-

senger i n i d e n t i f y i n g the s i g n a l a s being a t u rn s i g n a l o r a

s t o p s i g n a l were measured. I f sub jec t s made an e r r o r i n respond-

i ng t o a s i g n a l they cor rec ted the e r r o r a s soon a s it became

apparent t o them and depressed t h e appropr ia te switch. I t should

be noted t h a t e r r o r s were only recorded from the passenger ' s

response s ince he was car ry ing o u t a choice r eac t ion time. The

d r i v e r s u b j e c t c a r r i e d ou t a simple r eac t ion time t a s k , depress-

ing a s i n g l e switch i r r e s p e c t i v e of t he type of s i g n a l being

given. Table 1.5 shows t h e ana lys i s of the i d e n t i f i c a t i o n e r r o r s

f o r each s i g n a l mode i n each system f o r high and low s i g n a l in ten-

s i t y t e s t s .

I t w i l l be seen t h a t system 1 incurred the l a r g e s t number of

e r r o r s and system 8 t he fewest , A Cochran-Q t e s t on systems and

modes y ie lded non-s ign i f ican t r e s u l t s . There were a t o t a l of 1 1 4

e r r o r s made f o r t he 3200 t r i a l s t o which the passenger responded,

providing an e r r o r r a t e of 3.56 percent .

Missed Signals Analysis. When a s u b j e c t d id no t respond

within e i g h t seconds a f t e r t he i n i t i a t i o n of a s i g n a l by the lead

c a r t he response time was recorded as a missed s i g n a l . Such s ig -

n a l s were repeated a t a l a t e r time during t h e t r i a l s , This was

done s o a s no t t o incur missing da t a i n t h e ana lys i s of var iance.

Table 1 . 6 shows t h e frequency of missed s i g n a l s i n each s i g n a l

mode f o r each system i n t he high and low s i g n a l i n t e n s i t y tests

a s a t o t a l f o r both d r i v e r s and passengers.

Jt w i l l be noted t h a t t h e r e were a t o t a l of 115 missed s ig -

n a l s , ou t of 6 4 0 0 t r i a l s , f o r a missed s i g n a l r a t e of 1 . 7 9 per-

cent . Almost ha l f t he missed s i g n a l s occurred on system 1 with

fewest on system 8 , A Cochran-Q test showed t h a t t h e r e were

Mode - Turn

S t o p

Turn-Stop

Stop-Turn

System

Sum

TABLE 1.5, NUMBER OF ERRORS I N SIGNAL IDENTIFICATION. DATA FOR 40 PASSENGERS

Sys tern Mode I n t e n s i t y 1 3 4 6 8 - Sum

L 3 - 1 - 2 - 2 - 3 - 11 - T o t a l 7 5 6 7 6 31

H 1 1 1 1 0 4

L 4 - 1 - 2 - 3 - 0 - 10 - T o t a l 5 2 3 4 0 1 4

H 10 4 8 7 1 30

L 6 - 2 - 4 - 3 - 1 - 16 - T o t a l 16 6 12 10 2 46

H 2 2 3 0 3 10

L 3 - 3 - 2 - 3 - 2 - 13 - T o t a l 5 5 5 3 5 23

H 17 11 16 13 7

L 16 - 7 - 10 - 11 - 6 - T o t a l 33 18 26 24 1 3

Mode - Turn

S t o p

TABLE 1.6. NUMBER OF MISSED SIGNALS. DATA FOR 80 SUBJECTS

System I n t e n s i t y 1 3 4 6 8

L 1 - 1 - 0 - 3 - 1 - T o t a l 2 3 2 3 2

H 3 1 2 1 2

L 4 - 0 - 2 - 0 - 1 - T o t a l 7 1 4 1 3

Turn-Stop H 16 7 5 1 0

L 20 - 7 - 5 - 0 - 0 -

Mode Sum -

T o t a l 36 14 10 1 0 6 1

Stop-Turn H 2 4 3 3 0 12

L 3 - 3 - 1 - 3 - 4 - 14 - T o t a l 5 7 4 6 4 26

System

Sum

H 2 2 1 4 12 5 3

L 28 - 11 - 8 - 6 - 6 - T o t a l 50 25 20 11 9

s t a t i s t i c a l l y s i g n i f i c a n t d i f f e r e n c e s i n t h e number of s i g n a l s

missed by t h e systems and between t h e s i g n a l modes. I t w i l l be

noted t h a t t h e g r e a t e s t number of missed s i g n a l s occurred on

t h e tu rn - s top mode i n which system 1 had by f a r t h e h i g h e s t f r e -

quency of missed s i g n a l s and system 8 had none. I t was a l s o of

i n t e r e s t t o n o t e t h a t d r i v e r s i n c u r r e d 3 8 and passengers 77

missed s i g n a l s .

S i g n a l E f f e c t i v e n e s s Rat ings . Following each run wi th a

p a r t i c u l a r system t h e s u b j e c t s r a t e d it f o r i t s e f f e c t i v e n e s s

i n g i v i n g t u r n and s t o p s i g n a l s . Table 1 .7 shows t h e mean r a t i n g s

f o r each system i n t h e h igh and low s i g n a l i n t e n s i t y tests f o r

d r i v e r s and passengers . An a n a l y s i s of v a r i a n c e c a r r i e d o u t

a c r o s s s i g n a l systems of t h e s e r a t i n g s showed a h i g h l y s i g n i f i -

c a n t e f f e c t ( p < . 0 1 ) . A Newman-Keuls test showed t h a t system 8

was r a t e d s i g n i f i c a n t l y h i g h e r than a l l o t h e r s whi le system 6

was s i g n i f i c a n t l y p r e f e r r e d t o systems 4 , 3 and 1. Systems 4

and 3 were r a t e d s i g n i f i c a n t l y b e t t e r than system 1 (Table 1 . 8 ) .

THE EFFECT OF ALCOHOL UPON RESPONSE TO SIGNALS GIVEN BY

REAR L I G H T I N G AND SIGNALING SYSTEMS.

I n t r o d u c t i o n , Because a lcoho l i s r e p o r t e d t o be involved

i n a t l e a s t 50 p e r c e n t of t r a f f i c f a t a l i t i e s (Na t iona l S a f e t y

Council , 1968) and s i n c e rear-end c o l l i s i o n s a r e a l a r g e propor-

t i o n of two-car a c c i d e n t s and a r e involved i n 10 p e r c e n t of high-

way f a t a l i t i e s it was cons idered impor tant t o determine whether

t h e e f f e c t of a l c o h o l was d i f f e r e n t according t o t h e type of

s i g n a l system be ing used. I t was sugges ted t h a t a s a f e t y advan-

t a g e of improved s i g n a l systems may accrue t o t h e i n d i v i d u a l

under t h e i n f l u e n c e of a l c o h o l . I n a d d i t i o n , l i t t l e work has

been c a r r i e d o u t concerned wi th t h e i n t e r a c t i o n of n i g h t d r i v i n g

and a l c o h o l i n t a k e , excep t f o r one s imula t ion s tudy concerned

wi th t h e e f f e c t of headlamp g l a r e (Mortimer, 1963; Carpen te r , 1962) .

I n t h i s s tudy two automobile r e a r l i g h t i n g systems were e v a l -

ua ted wi th t h e s u b j e c t s both sober and wi th low l e v e l s of a l coho l

TABLE 1.7. MEAN SIGNAL EFFECTIVENESS RATINGS FOR EACH SYSTEM, INTENSITY AND TASK

System High Intensity 1 3 4 6 8

D (N=23) 4.391 6.217 6.521 6.956 7.347

P (N=23) 3.826 5.695 5.695 6.913 8.086

Low Intensity

Mean 4.593 6.162 6.279 6.930 7.697

TABLE 1.8. INDIVIDUAL COMPARISONS OF MEAN SYSTEM SIGNAL EFFECTIVENESS RATING BY l@WMAN-KEULS TEST

System 8, 6, 4, 3 rated significantly1 better than 1

System 8 rated significantly better than 6, 4, 3, 1

System 6 rated significantly better than 4

'significant at P 5 - .05

i n a w e l l d e f i n e d exper imenta l s i t u a t i o n , The approach promised

t o have a h igh payoff s i n c e i n o u r s o c i e t y most d r ink ing-dr iv ing

occurs a t n i g h t when t h e e f f i c i e n c y of automobile r e a r l i g h t i n g

systems may be a b l e t o reduce t h e h igh f a t a l i t y r a t e (HSRI, 1 9 6 9 ) . Method. Thir ty-two s u b j e c t s were used o v e r a l l wi th s i x t e e n

s e r v i n g a s d r i v e r s and s i x t e e n a s passengers , S u b j e c t s were

v o l u n t e e r s who had responded t o n o t i c e s t o p a r t i c i p a t e i n t h e

test and were p a i d f o r t h e i r s e r v i c e s . A l l had consented t o t a k e

s m a l l amounts of an a l c o h o l and orange j u i c e combinat ion, The

age range was 2 1 t o 47 y e a r s ,

The procedure was t h e same a s t h a t used i n t h e p rev ious t e s t , us ing presence l i g h t s a t 2.7 cp and s i g n a l s a t 35 cp.

P r i o r t o r e p o r t i n g f o r t h e test each s u b j e c t was s e n t i n s t r u c -

t i o n s r e q u e s t i n g t h a t they o b t a i n a normal n i g h t of s l e e p b e f o r e

t h e experiment and t o r e f r a i n from u s i n g a l c o h o l and o t h e r drugs ,

and t o have concluded d inner by 6:15 p.m. on t h e n i g h t of t h e

test . S u b j e c t s were run i n p a i r s , u s u a l l y male-female, i n t h e

exper imenta l s e s s i o n which s t a r t e d a t approximately 8 p.m. and

l a s t e d f o r f o u r hours . A l l s u b j e c t s were p icked up and r e t u r n e d

t o t h e i r r e s i d e n c e s . S u b j e c t s were p r e - t e s t e d f o r c o l o r b l i n d -

n e s s and on ly normal c o l o r v i s i o n i n d i v i d u a l s were used,

The procedure f o r each p a i r of s u b j e c t s was t h e same. A

c o i n t o s s decided who would be t h e passenger of t h e f i r s t p a i r

and of a l l same sexed p a i r s ; a l l o t h e r s were a l t e r n a t e d each

n i g h t by t a s k .

The s u b j e c t s were s e a t e d i n t h e fo l lowing v e h i c l e and were

read t h e i n s t r u c t i o n s which exp la ined t h e t a s k . Then a denon-

s t r a t i o n of each of t h e f o u r s i g n a l modes of t h e p r a c t i c e system1

was given whi le t h e s u b j e c t s responded t o a l l t a s k s accord ing ly .

When it was c l e a r t h a t they understood t h e procedure a normal

l e n g t h run of 1 6 t r i a l s ( 4 random p r e s e n t a t i o n s of each of t h e

4 s i g n a l modes) was made f o r f a m i l i a r i z a t i o n purposes. They

then c a r r i e d o u t t h e s i g n a l system e f f e c t i v e n e s s r a t i n g pro-

' system 6 , i n t h e p rev ious tests.

4 1

cedure. Subjects then re turned t o the laboratory where they

signed r e l ea se forms, and were weighed.

Other da t a , such a s name, age and drinking frequency in for -

mation was co l l ec t ed by one experimenter while t he f i r s t dose

was prepared by t h e o ther experimenter. This was done by mea-

sur ing orange juice dr inks equal i n milliliters t o t he body

weight times 1.5. The sub jec t s were given the dr inks and told:

"These dr inks may or may not contain a lcohol i n various s a f e

amounts. You may not be able t o t a s t e o r smell any alcohol.

Please consume the dr inks during t h e next t en minutes. Do not

d i scuss t he q u a l i t y o r t a s t e of t he drink nor what you consider

t o be i t s content ." The experimenters a l s o drank orange juice

and conversed with t he sub jec t s . After a t en minute wai t ing

period from the end of the drinking period a Borkenstein

Brea tha l ize r , model 9 0 0 , was used t o determine blood a lcohol

Levels. Both t h e d r ive r and passenger took breath tests.

The sub jec t s then re turned t o t he t e s t ca r s and were given

a demonstration of t he four s i g n a l modes of the f i r s t r e a r l i g h t -

ing system with which they would work. They were i n s t ruc t ed t o

continue responding t o a l l s i g n a l l i g h t s and t o follow the lead

c a r a t a normal, s a f e dis tance. After the sub jec t s had received

s ix t een s i g n a l s , four i n each s i g n a l mode, t he veh ic les were

stopped and the sub jec t s r a t ed the system f o r e f fec t iveness i n

giving s igna l s . The d ther system t o be t e s t e d was then demon-

s t r a t e d and s ix t een t r i a l s were run with it. A t t he conclusion

of those runs t h e system was r a t ed as before and the sub jec t s

re turned t o the laboratory.

The sub jec t s were then administered dose 2 which was t h e

same as dose 1 f o r t he d r ive r ; f o r t he passenger dose 2 consis-

t e d of t h e following orange juice and alcohol composition:

Total Volume = body weight ( l b s ) x 1.5 m l

Alcohol Volume = body weight ( l b s ) x .35 m l The sub jec t s were i n s t ruc t ed t o consume dose 2 wi thin ten min-

u t e s and a t t he conclusion of another f i f t e e n minutes, a

brea tha l i ze r t e s t was made.

Results.

Reaction Time. Each react ion time t o a s ignal was t rans-

formed t o loge and an analys is of variance of the transformed

react ion time data was car r ied o u t , The analysis of variance

(Table 1 . 9 ) found s i g n i f i c a n t e f f e c t s due t o task , s igna l system,

system x sex, s igna l mode, mode x task and system x dose x sex

x task. Table 1 . 1 0 shows the geometric mean react ion times t o

the two l i g h t i n g systems i n each s igna l mode. The r e s u l t s of a

Newman-Keuls t e s t on these data a re a l so shown i n Table 1 . 1 0 and

indica te t h a t system 8 i s s i g n i f i c a n t l y superior t o system 1 i n

the turn , turn-stop, and stop-turn modes. There was no s i g n i f i -

cant difference i n the s top mode.

Table 1.11 shows the geometric mean reac t ion time fo r the

two systems by sex of subjec t , showing t h a t females had longer

react ion times than males i n system 1. The geometric mean

react ion times fo r the four f ac to r in te rac t ion of sex, t a sk ,

alcohol dose and system a re shown i n Table 1 . 1 2 . An i n i t i a l

indica t ion of the e f f e c t of alcohol can be obtained by compar-

ing dose 1 and dose 2 f o r the passengers. This shows t h a t

react ion time decreased fo r system 1 and increased on system 8

f o r males; while mean react ion time increased i n system 1 and

no change occurred on system 8 f o r females.

Another ana lys is took i n t o account the cont ro l ro le of the

d r i v e r over the f ixed order of alcohol treatment administration.

The r e l a t i v e response time i n dose 1 f o r passenger ( P ) and dr iver

( D ) would be expected t o be the same as i n dose 2 i f alcohol has

no e f f e c t , the only e f f e c t s being due t o random var i a t ion , fa t igue

and p rac t i ce , I f alcohol has an a f f e c t then dose 2 r a t i o s of P/D

w i l l be l a rge r than P/D fo r dose 1 , Thus, values above uni ty i n

Table 1.13 show such an e f f e c t a t t r i b u t a b l e t o alcohol and random

var ia t ion . The comparison shows t h a t males were l e s s affected

on system 1 than system 8 , though they were impaired i n both;

while f e m a l e ~ ~ w e r e more impaired i n system 1 than system 8 and

TABLE 1.9, ANALYSIS OF VARIANCE OF REACTION TIME TO SIGNALS FOR TWO REAR LIGHTING SYSTENS, WITH AND WITHOUT ALCOHOL. DATA FOR 32 SUBJECTS

Source

Between Groups

Task (T)

Sex (Sx)

T x Sx

Subjects w. Grp

Within Groups

System (Sy)

Sy x Sx

Sy x T

Sy x Sx x T

Sy x Subj w. Grp

Mode (M)

M x Sx

M x T

M x S x x T

M x Subj w. Grp

Dose (D)

D x Sx

D x T

D x S x x T

D x Subj w, Grp

TABLE 1.9. ANALYSIS OF VARIANCE OF REACTION TIME TO SIGNALS FOR TWO REAR LIGHTING SYSTEMS, WITH AND WITHOUT ALCOHOL. DATA FOR 32 SUBJECTS (Continued)

Source SS df - MS - F - Sy x M 40.907 3 13.635 83.47**

Sy x M ,392 3 .I31 ---- S y x M x T .461 3 .153 ---- Sy x 14 x T .079 3 ,026 ---- Sy x M x Subj w. Grp 13.721 84 .163 ----

Sy x D .416 1 .416 2.11

Sy x D x Sx .092 1 .092 ---- S y x D x T .I25 1 .125 ---- S y x D x S x x T .958 1 .958 4.83*

Sy x D x Subj w. Grp 5.530 28 .197 ----

M x D ,638 3 . 212 1.38

M x D x S x 1.145 3 ,381 2.47

M x D x T .504 3 -168 1.09

M x D x S x x T .197 3 .065 ---- M x D x Subj w. Grp 12.936 84 ,154 ----

M x D x S y ,490 3 . 163 ---- M x D x S y x S x .245 3 .081 ---- M x D x S y x T .403 3 ,134 ---- M x D x S y x S x x T .I55 3 ,051 ---- M x D x Sy x Subj w. Grp 14.492 84 .172 ----

Within Cells 230.719 1536 .I50 ----

Total 528.952 2047

TABLE 1.10. GEOMETRIC MEAN REACTION TIME (SECONDS) TO LIGHTING SYSTEMS AND SIGNAL MODES, DATA FO3 32 SUBJECTS

System Turn Stop Turn-Stop Stop-Turn - 1 1.277 1.067 1.196 2.244

8 1.118 1,011 ,945 1.032 - Mean 1.198 1.039 1,071 . 1.638

Mean - 1.446

1.027

Individual Comparisons by Newman-Keuls Tests:

1. Turn: 8 signif icantlyl better than 1

2. Stop: No significant difference

3. Turn-Stop: 8 significantly better than 1

4. Stop-Turn: 8 significantly better than 1

- - - . - - - - - - -

'significant at P 2 .01. -

TABLE 1.11. GEOMETRIC MEAN REACTION TIME (SECONDS) FOR SYSTEMS AND SEX OF SUBJECT IN THE ALCOHOL EX- PERIMENT. DATA FOR 32 SUBJECTS

System

1

8

Sex Male - Female

1.314 1.455

TABLE 1.12. GEOMETRIC MEAN REACTION TIME (SECONDS) AS A FUNCTION OF SEX, TASK, ALCOHOL DOSE ' , AND SYSTEM. DATA FOR 32 SUBJECTS

Male Female

Driver Passenger Driver Passenger System Dose Dose Dose Dose

'~ose - 1: No alcohol for Driver or Passenger Dose - 2: No alcohol for Driver; Alcohol for Passenger

TABLE 1.13. RELATIVE IMPAIRMENT (R I) ' IN REACTION TIME DUE TO ALCOHOL DOSE FOR SEX AND SYSTEM, CONTROLLED FOR ORDER EFFECTS

System Sex 1 8

Male 1.011 1.129

Female 1.161 0.918

Mean Passenger R.T. + Dose - Mean Driver R.T. 1 Mean Passenger R.T. + Dose - Mean Driver R.T. 1

a c t u a l l y had lower response times i n system 8 i n t h e a l c o h o l con-

d i t i o n . O v e r a l l t h e r e was s l i g h t l y less impairment i n system 8

than system 1.

S i g n a l I d e n t i f i c a t i o n E r r o r s , The number of e r r o r s made

t o each system i n each s i g n a l mode a s a f u n c t i o n of t h e a l c o h o l

c o n d i t i o n i s shown i n Table 1 . 1 4 , These d a t a a r e on ly f o r t h e

passengers because t h e d r i v e r was c a r r y i n g o u t a s imple r e a c t i o n

time t a s k which d i d n o t permi t measurement of s i g n a l i d e n t i f i c a -

t i o n e r r o r s . The t o t a l number of e r r o r s made i n t h e s e tests was

40, f o r an e r r o r r a t e of 3 .91 p e r c e n t , which compares wi th an

e r r o r r a t e of 3.56 pe rcen t found i n t h e previous tests. There

were r e l a t i v e l y more e r r o r s made on system 8 , compared t o system

1, i n t h i s t e s t than t h e two previous tests. There were 50 per-

c e n t more e r r o r s under a l c o h o l c o n d i t i o n s than non-alcohol b u t

most of t h i s d i f f e r e n c e was due t o male s u b j e c t s .

Missed S i g n a l s Analys is . The number of s i g n a l s missed

i n each system and s i g n a l mode i n t h e two a l c o h o l c o n d i t i o n s a r e

shown i n Table 1.15. I t w i l l be noted t h a t t h e r e were more s i g -

n a l s missed i n dose 1 (non-alcohol) cond i t ion than i n t h e a lco-

h o l c o n d i t i o n , I t w i l l a l s o be noted t h a t t h e r e were consider-

a b l y fewer s i g n a l s missed on system 8 i n both dose c o n d i t i o n s

compared wi th system 1. This d i f f e r e n c e was h i g h l y s i g n i f i c a n t

s t a t i s t i c a l l y . The r e s u l t s do n o t show any d e t r i m e n t a l e f f e c t

of a l c o h o l i n t h i s a n a l y s i s .

Rat ing of S i g n a l System E f f e c t i v e n e s s . The r a t i n g s

of t h e d r i v e r s and passengers of s i g n a l system e f f e c t i v e n e s s

which were made a t t h e conclus ion of runs wi th each system i n

both a l c o h o l c o n d i t i o n s d i d n o t show any e f f e c t s of a l c o h o l .

There was a h i g h l y s i g n i f i c a n t d i f f e r e n c e between t h e mean r a t i n g s

achieved by system 1 and system 8 a s shown by an a n a l y s i s of

va r i ance .

The mean r a t i n g s f o r system 1 and system 8 were: (1) -3 ,703

and (8)-7.766. I t w i l l be noted t h a t t h e s e va lues a r e c l o s e t o

t h o s e ob ta ined i n previous t e s t s , showing a s t r o n g p re fe rence

f o r system 8 . 48

TABLE 1.14. NUMBER OF ERRORS IN SIGNAL IDENTIFICATION FOR SYSTEMS AND DOSES. DATA FOR 16 SUBJECTS

Dose System 1 2 Total

Total 16 24 40

TABLE 1.15. NUMBER OF MISSED SIGNALS FOR SYSTEMS, MODES AND DOSES. DATA FOR 32 SUBJECTS

Dose (1) No-Alcohol Mode

Turn Stop System S stem Turn Stop Stop Turn Total Y- - 1 2 9 28 1 40

8 0 - 2 - 0 - 1 - 3 - Total 2 11 28 2 43

Dose ( 2 ) Alcohol Mode

Turn Stop System System Turn Stop Stop Turn Total -

8 5 - 1 - 0 - 0 - 6 - Total 5 4 22 2 33

2. DETERMINATION OF INTENSITY VALUES FOR REAR SIGNAL LIGHTS (TASK 2)

S t u d i e s were conducted i n o r d e r t o c o l l e c t d a t a on i n t e n -

s i t y requi rements f o r s i g n a l lamps t o be used a t t h e r e a r of

v e h i c l e s , s o t h a t recommendations concerning s i g n a l l i g h t i n t e n -

s i t y under v a r i o u s ambient l i g h t i n g c o n d i t i o n s could be made.

P r i n c i p a l l y , day and n i g h t d r i v i n g c o n d i t i o n s p rov ide t h e major

s u b d i v i s i o n of ambient l i g h t i n g . Within daytime l e v e l s t h e r e

a r e c o n s i d e r a b l e v a r i a t i o n s i n t h e i l l u m i n a t i o n and, hence, i n

t h e luminance and c o n t r a s t of o b j e c t s seen i n t h e d r i v e r ' s v i s u a l

f i e l d . For t h i s reason it was cons ide red impor tan t t o a t t e m p t

t o c a r r y o u t t h e s tudy over a reasonably r e p r e s e n t a t i v e range of

daytime ambient i l l u m i n a t i o n l e v e l s s o t h a t b r i g h t , sunny and

cloudy d u l l days were proposed t o be used. The o t h e r v a r i a b l e s

i n which a d d i t i o n a l d a t a were f e l t t o be needed were t h o s e con-

cerned wi th t h e requi rements f o r t h e i n t e n s i t i e s of s i g n a l lamps

having v a r i o u s c o l o r s and f o r t h i s reason r e d , green-blue, amber

and a l s o whi te were used. The reason f o r t h e i n c l u s i o n of whi te

i n t h e s e tests was t o use a l i g h t which i s n o t dependent upon

c h a r a c t e r i s t i c s of s p e c i f i c c o l o r f i l t e r s and m a t e r i a l s and

which can , t h e r e f o r e , s e r v e a s a s t a n d a r d f o r comparison wi th

o t h e r s t u d i e s t h a t have a l r e a d y been c a r r i e d o u t and t h o s e t h a t

may be c a r r i e d o u t i n t h e f u t u r e . I n t h i s way t h e responses t o

t h e whi te can be r e l a t e d t o t h o s e t h a t were ob ta ined f o r t h e

co lo red l i g h t s and i s a means of a s s e s s i n g t h e r e f e r e n c e assumed

by t h e s u b j e c t s i n making t h e i r s u b j e c t i v e e v a l u a t i o n s .

Other s t u d i e s have a l r e a d y been conducted concerned w i t h t h e

q u e s t i o n of i n t e n s i t y requi rements for v e h i c l e l i g h t s a t n i g h t ,

i n daytime and i n f o g , I t has been shown (Forbes , 1966; AMA

Vehicle L i g h t i n g Committee T e s t s , 1958-64) t h a t an i n t e n s i t y

which p rov ides s u f f i c i e n t v i s i b i l i t y i n t h e daytime w i l l cause

d i scomfor t g l a r e a t n i g h t (Ki lgour , 1962) . For example, t h e

Road Research Laboratory (1963) has sugges ted t h a t 2000 cande las i n

t h e day and 100 candelas a t n i g h t would r e s u l t i n a more e f f i -

c i e n t s i g n a l system.

S t u d i e s c a r r i e d o u t t o cons ide r i n t e n s i t y requirements f o r

t r a f f i c s i g n a l s (Boisson and Pages, 1964; Cole and Brown, 1965,

1966a, 1966b; Rut ley , C h r i s t i e & F i s h e r , 1965; Adrian, 1964)

found t h a t i n t e n s i t i e s between 200-800 cp a r e r e q u i r e d , depen-

den t upon lamp a r e a . The f i n d i n g s can be i n t e r p r e t e d t o i n d i -

c a t e t h a t a lamp of approximately 20 square inches would r e q u i r e

about 200 cp f o r adequate v i s i b i l i t y i n daytime under most v i s u a l

backgrounds of ambient i l l u m i n a t i o n , These d a t a have d i r e c t

a p p l i c a t i o n t o t h e p r e s e n t problem.

A more r e c e n t s tudy by King and Finch (1969) found t h a t

under b r i g h t daytime c o n d i t i o n s a whi te l i g h t should have approxi-

mately 2000 cp f o r a luminous a r e a of 20 square inches t o be con-

s i d e r e d adequate under t h e c r i t e r i o n t h a t they used,

Data of t h e s e types have i n d i c a t e d very c l e a r l y t h a t a

s i n g l e i n t e n s i t y l e v e l f o r v e h i c l e s i g n a l l i g h t s cannot meet

adequate v i s i b i l i t y requirements under t h e v a r i e t y of ambient

c o n d i t i o n s i n which d r i v i n g i s c a r r i e d o u t . There has been d i s -

c u s s i o n , f o r a number of y e a r s , concerned wi th t h e p o s s i b i l i t y

of i n t r o d u c i n g a t l e a s t a two i n t e n s i t y l e v e l s i g n a l system t o

account f o r t h e major s h i f t s i n ambient l e v e l encountered i n

n i g h t and day d r i v i n g cond i t ions . Other c o u n t r i e s have a l r e a d y

i n s t i g a t e d a c t i o n i n o r d e r t o implement such a two l e v e l s t o p

s i g n a l system, and i n England t h e recommendations p r e s e n t l y sug-

g e s t t h a t daytime minimum and maximum s t o p l i g h t va lues should

be 130 cp and 520 cp wi th corresponding minimum and maximum v a l u e s

f o r n igh t t ime s i g n a l s t o be 30 cp and 120 cp. These l e v e l s a r e

based on tests which were c a r r i e d o u t by t h e Automobile Manufac-

t u r e r s Assoc ia t ion i n t h e U.S. (1958-1965). I t i s expected t h a t

a d u a l i n t e n s i t y system w i l l be in t roduced a s a requirement on

a l l v e h i c l e s i n England w i t h i n about two yea rs . I n a d d i t i o n , it

should be noted t h a t some B r i t i s h c a r s a l r e a d y have a v a i l a b l e

a s an op t ion a d u a l i n t e n s i t y r e a r s i g n a l i n g system. I n

A u s t r a l i a t h e proposed requirements a r e s t i p u l a t e d i n A u s t r a l i a n

Design Nos. 6 and 7 (ADR 6 & 7, 1968) .

~ u s t r a l i a n r e g u l a t i o n s a r e t h e same a s t h o s e proposed i n

England and Europe (ECE, R9gulation Nos. 6 & 7, Turn I n d i c a t o r s ,

and p o s i t i o n Lamps, Rear Lamps and Stop Lamps) . I t appears t h a t

i n France t h e ECE requirements have a l r e a d y been adopted.

ECE Regulat ion 7 (1967) sugges t s a range of 130 cp-520 cp i n

t h e day and 30 cp-120 cp a t n i g h t f o r s t o p lamps. For d i r e c t i o n

i n d i c a t o r s t h e corresponding va lues a r e 175 cp-700 cp i n t h e day

and 40 cp-120 cp a t n i g h t a s s t a t e d i n ECE Regulat ion No. 6 (1967).

These r e g u l a t i o n s , t h e r e f o r e , i n d i c a t e an awareness of a

need t o implement a d u a l - i n t e n s i t y system f o r o p e r a t i o n i n day

and n i g h t cond i t ions . I t has been sugges ted (Finch, 1968) t h a t

an a d d i t i o n a l i n t e n s i t y may be r e q u i r e d t o account f o r both day-

time and n igh t t ime fog c o n d i t i o n s , o r o t h e r c o n d i t i o n s i n which

atmospheric t r ansmiss ion i s cons ide rab ly degraded. Finch has

sugges ted t h a t minimum night:day:fog i n t e n s i t i e s should be i n

t h e r a t i o of 1:4:16, though he recommends r a t i o s of 1:10:100 t o

more adequate ly meet t h e v i s i b i l i t y requirements . H e has sug-

ges ted t h a t s t o p s i g n a l s should have an i n t e n s i t y of 60 cp-120 cp

a t n i g h t , minimum of 240 cp i n t h e day and a minimum of 960 cp i n

fog cond i t ions . I t i s worth n o t i n g t h a t some lamp manufacturers have i n t r o -

duced h igh i n t e n s i t y r e d , r e a r presence lamps which would be

manually turned on by t h e d r i v e r under low v i s i b i l i t y cond i t ions

(Anon, 1 9 6 6 ) . The very severe a t t e n u a t i o n of l i g h t of a l l c o l o r s

under fog cond i t ions has been amply demonstrated i n previous theo-

r e t i c a l and exper imenta l work (Middleton, 1963; Moore and R u f f e l l

Smith, 1 9 6 6 ; Finch, 1 9 6 8 ; Mortimer, 1969a) . Therefore , l a r g e

i n c r e a s e s i n i n t e n s i t y a r e r equ i red i n o r d e r t o r e t a i n v i s i b i l i t y

of r e a r l i g h t i n g i n water vapor fog and o t h e r types of atmospheric

c o n d i t i o n s which reduce t h e t r ansmiss ion of l i g h t .

The s t u d i e s t o be desc r ibed were n o t concerned wi th evalua-

t i o n of l i g h t i n t e n s i t y requirements under degraded cond i t ions .

They were, however, in tended t o provide some a d d i t i o n a l informa-

t i o n which may be u s e f u l f o r t h e s p e c i f i c a t i o n of r e a r s i g n a l -

i n g and l i g h t i n g i n t e n s i t y requirements i n t h e more u s u a l , normal

day and n i g h t d r i v i n g c o n d i t i o n s , p a r t i c u l a r l y t o provide i n f o r -

mation cover ing more v a r i a b l e s than have been p rev ious ly system-

a t i c a l l y s t u d i e d .

F i n a l l y , it should a l s o be noted t h a t p r e s e n t recommenda-

t i o n s f o r s i g n a l and presence l i g h t i n t e n s i t i e s a r e s p e c i f i e d

i n terms of candlepower. This u n i t of measurement a lone i s

inadequate because t h e c r i t e r i o n performance of a l i g h t , such

a s i t s b r i g h t n e s s , i s dependent upon i n t e n s i t y and a l s o luminous

a rea . For t h i s reason candelas may be used t o make recommenda-

t i o n s f o r lamp i n t e n s i t y i n a reasonable manner i f t h e lamp a r e a

i s a l s o s t a t e d , and an a p p r o p r i a t e a r e a c o r r e c t i o n f a c t o r i s

a p p l i e d , Another o b j e c t i v e of t h e s e s t u d i e s was t o determine

such f a c t o r s .

DAY AND N I G H T OUTDOOR INTENSITY TEST.

Method . Apparatus. The t e s t lamps were General E l e c t r i c Co.

4405 s p o t lamps each mounted i n a s p e c i a l housing a t t a c h e d t o

a grey , 4 0 % r e f l e c t a n c e board, 4 x 6 f e e t , supported one f o o t

above t h e ground (Figure 2.1) . Four lamps were mounted on t h e

board t h r e e of them a s c l o s e t o g e t h e r h o r i z o n t a l l y a s p o s s i b l e

and a t t h e same h e i g h t , 2 4 inches a x i a l l y above t h e ground,

whi le a f o u r t h lamp was cen te red above t h e o t h e r t h r e e a t an

a x i a l h e i g h t of 46 inches . The lamps were mounted i n housings

which pe rmi t t ed t h e i n s e r t i o n of c o l o r f i l t e r s and masks by

which t h e lamp luminous a r e a could be changed. The lamps were

4 inches i n d iameter and t h e t h r e e lamps i n t h e lower p o r t i o n

of t h e board were separa ted by an edge-to-edge d i s t a n c e of 2 . 0

inches . This pe rmi t t ed i n v e s t i g a t i o n of v a r i a t i o n s i n lamp a r e a

which could be ob ta ined by t h e use of 1, 2 o r 3 of t h e s e lamps

53

Figure 2 . 1 . Arrangement of t h e t e s t lamps behind t h e surround board.

s imul taneously l i g h t e d , t o provide a f a i r l y uniform, v a r i a b l e

l i g h t e d a r e a .

Power t o t h e lamps was provided by an Eico b a t t e r y charger

which f e d i n t o a l i n e a r ramp v o l t a g e g e n e r a t o r . A c o n t r o l box

was provided, c o n t a i n i n g a vo l tme te r f o r v i s u a l monitoring of

t h e i n p u t v o l t a g e , swi tch ing c i r c u i t s and a v a r i a b l e t ime base

g e n e r a t o r f o r t h e i n p u t vo l t age . Each lamp was i n d i v i d u a l l y

switched s o t h a t any number of t h e f o u r lamps could be l i g h t e d

a s r equ i red . The v o l t a g e i n p u t t o each lamp was recorded on

one channel of a two-channel Brush, s t r i p - c h a r t r ecorder (F igure

2 . 2 ) .

Photometry. P r i o r t o t e s t i n g and a t v a r i o u s i n t e r v a l s

dur ing t h e t e s t t h e l i g h t o u t p u t from t h e lamps was measured and

c a l i b r a t e d a g a i n s t t h e lamp i n p u t v o l t a g e . These c a l i b r a t i o n s

were c a r r i e d o u t a t n i g h t by measuring t h e i l l u m i n a t i o n f a l l i n g

on a t e s t p l a t e of known r e f l e c t a n c e which was p laced a t about

t h e l o c a t i o n of t h e eyes of t h e s u b j e c t s dur ing t e s t s . The i l l u -

minat ion measurements were then conver ted t o candlepower read ings

and i n t h i s way, f o r each combination of lamps and c o l o r s , v o l t a g e

i n p u t and candlepower o u t p u t was known.

The photometr ic measurements were made us ing t h e Spec t ra

P r i t c h a r d photometer which had been c a l i b r a t e d a g a i n s t a Macbeth

I l luminometer f o r t h e c o l o r s used i n t h e t e s t a s w e l l a s whi te

l i g h t .

Sub jec t Response I n d i c a t o r s . The t e s t s u b j e c t s were

s e a t e d i n a v e h i c l e a t t h e r e q u i r e d d i s t a n c e from t h e board sup-

p o r t i n g t h e test lamps. Two s u b j e c t s were i n t h e f r o n t s e a t ; one

s u b j e c t was i n t h e r e a r s e a t looking between t h e f r o n t s e a t sub-

j e c t s . An experimenter was a l s o i n t h e s u b j e c t c a r . The s u b j e c t s

were each given a s i l e n t pushbutton swi tch which they could hold

i n t h e palm of one hand and o p e r a t e wi th t h e thumb. Whenever a

s u b j e c t depressed a swi tch a mark was made on one channel of t h e

s t r i p - c h a r t r e c o r d e r l o c a t e d a t t h e test lamp board. I n t h i s way

F i g u r e 2 . 2 . Lamp i n t e n s i t y c a l i b r a t i o n and c o n t r o l system and d a t a c h a r t r e c o r d e r .

5 6

s u b j e c t responses could be e a s i l y c o r r e l a t e d w i t h t h e p r e v a i l i n g

v o l t a g e i n p u t t o t h e test lamps which was recorded on t h e second

channel , and, hence, t h e i r responses could then be r e l a t e d

d i r e c t l y t o lamp i n t e n s i t y .

Independent v a r i a b l e s . The v a r i a b l e s of i n t e r e s t i n t h i s s tudy were t h e l i g h t c o l o r , lamp a r e a , viewing d i s t a n c e .

ambient i l l u m i n a t i o n , and t h e c o l o r v i s i o n c h a r a c t e r i s t i c s of

t h e s u b j e c t s .

(1) Color . Three c o l o r s ( r e d , green-blue, and amber)

and whi te were used a s t h e t e s t s t i m u l i . The s p e c t r a l d i s t r i b u -

t i o n of t h e c o l o r e d l i g h t s i s shown i n F igure 2.3.

(2 ) Lamp Area. Five lamp a r e a s were used i n t h e s e

tests , which were ob ta ined e i t h e r by i n s e r t i n g an a p e r t u r e mask

over a s i n g l e lamp housing o r by i n c r e a s i n g t h e t o t a l number of

lamps used. The r e s u l t i n g luminous a r e a s of t h e lamps were: 4 ,

6 .1, 12.6, 25 .2 and 3 7 . 8 square inches .

( 3 ) Lamp Locat ion . I n o r d e r t o provide some i n d i c a -

t i o n of t h e e f f e c t of mounting lamps a t about t h e eye h e i g h t of

d r i v e r s a s i n g l e 4-inch d iameter lamp was mounted 46 inches

above t h e ground whereas t h e o t h e r t e s t lamps were mounted 2 4

inches above t h e ground. Comparison of r e s u l t s wi th t h i s lamp

and from an analogous lamp mounted a t t h e lower h e i g h t would

provide some i n d i c a t i o n of t h e e f f e c t of lamp h e i g h t .

( 4 ) Ambient L igh t ing . The most impor tan t i n v e s t i g a -

t i o n t o de termine t h e e f f e c t of ambient l i g h t i n g was t h e compari-

son of day and n igh t t ime c o n d i t i o n s . However, w i t h i n each day-

time c o n d i t i o n , measurements were con t inuous ly made of t h e lumi-

nance of t h e tes t lamp board i n o r d e r t o provide i n d i c a t i o n s of

t h e p r e v a i l i n g ambient i l l u m i n a t i o n i n daytime l e v e l s .

( 5 ) Viewing Dis tance , Two d i s t a n c e s were s e l e c t e d a t

which t h e s u b j e c t s would make o b s e r v a t i o n s of t h e test l i g h t s :

7 5 f e e t and 2 8 0 f e e t . I n both c o n d i t i o n s t h e s u b j e c t s viewed t h e

/ @

- /e

.@@-

/ /'

- lI I 0 -

I /

- I Amber / I -

I I - I I

I I

- / Red

- -

- -

- -

425 450 475 500 525 550 575 600 650 700 750

WAVELENGTH (MP)

Figure 2 . 3 . Spec t r a l d i s t r i b u t i o n of co lo r f i l t e r s .

lamps i n a l i n e p a r a l l e l t o t h e lamp axes.

( 6 ) V i sua l C h a r a c t e r i s t i c s of Observers . I t was a l s o

of i n t e r e s t t o o b t a i n in fo rmat ion based upon responses from obser-

v e r s who were c l a s s i f i e d a s color-normal a s w e l l a s those who a r e

color-abnormal. Color-abnormal s u b j e c t s were c l a s s i f i e d on t h e

b a s i s of a c o l o r - v i s i o n t e s t a s be ing e i t h e r deuteranopes o r

protanopes .

S u b j e c t s . A t o t a l of 6 4 s u b j e c t s were used i n t h e s e

tests , some of whom were used i n both day and n i g h t s e s s i o n s .

There were 27 females and 26 males wi th normal c o l o r v i s i o n , and

11 male d ichromates , 10 of whom were deuteranopes and one a pro-

tanope. A t o t a l of 87 s u b j e c t runs were made. A s u b j e c t run i s

de f ined a s t h e number of s u b j e c t s used i n an exper imenta l d a t a

c o l l e c t i o n s e s s i o n m u l t i p l i e d by t h e number of s e s s i o n s . A l l

s u b j e c t s d i d n o t p a r t i c i p a t e i n a l l t h e c o n d i t i o n s of t h e tes t .

For example, some s u b j e c t s were used on ly i n n i g h t t e s t s and

o t h e r s i n daytime.

Procedure. Daytime exper imenta l s e s s i o n s were u s u a l l y

s t a r t e d between 9 a.m. and 10:30 a.m., and n igh t t ime s e s s i o n s

began a f t e r s u n s e t between 7 p.m. and 8 p.m. An exper imenta l

s e s s i o n l a s t e d approximately one hour .

The s u b j e c t s were f i r s t admin i s t e red t h e Dvorine c o l o r -

b l i n d n e s s t e s t . The s u b j e c t s were then s e a t e d i n t h e v e h i c l e ,

two i n t h e f r o n t s e a t and one i n t h e r e a r . Each s u b j e c t was

given a s i l e n t , pushbutton swi tch which he was t o o p e r a t e wi th

t h e thumb. If c o l o r - b l i n d s u b j e c t s were involved i n a s e s s i o n

i n which obse rve rs w i t h normal c o l o r v i s i o n were a l s o be ing used

t h e i r responses were coded i n terms of t h e p o l a r i t y of t h e s t r o k e

made on t h e s t r i p c h a r t r e c o r d e r paper . This enabled t h e i r

r e sponses t o be s e p a r a t e d o u t from those made by color-normal sub-

j e c t s .

When t h e s u b j e c t s were s e a t e d i n t h e v e h i c l e they were read

t h e i n s t r u c t i o n s f o r t h e t e s t which a r e shown i n f u l l i n Appendix

A-1 .

5 9

During daytime s e s s i o n s t h e s u b j e c t s were t o l d t o respond

when t h e l i g h t appeared t o be of adequate b r i g h t n e s s f o r a s t o p

signal--"one which would c e r t a i n l y a t t r a c t your a t t e n t i o n . " I n

n igh t t ime s e s s i o n s t h e s u b j e c t s were t o respond whenever t h e

l i g h t appeared s o b r i g h t t h a t it was uncomfortable t o view--not

j u s t of such a b r i g h t n e s s t o be a t t e n t i o n - g e t t i n g f o r a s t o p s i g -

n a l , b u t " d e f i n i t e l y t o o b r i g h t . "

The s t i m u l i were p resen ted i n an ascending and a decending

o r d e r of lamp i n t e n s i t y . There fo re , v o l t a g e was g r a d u a l l y a p p l i e d

t o t h e lamp s o t h a t t h e l i g h t i n t e n s i t y would i n c r e a s e from ze ro

up t o a maximum l e v e l . When t h e maximum was reached t h e lamp was

e x t i n g u i s h e d f o r about h a l f a second and then aga in tu rned on a t

t h e maximum l e v e l . T h e r e a f t e r , t h e i n t e n s i t y was g r a d u a l l y

decreased u n t i l t h e lamp was ex t ingu i shed . The ascending and

decending r a t e of i n t e n s i t y was a u t o m a t i c a l l y c o n t r o l l e d and t h e

time pe r iod f o r each t r i a l was v a r i e d between 15 seconds and 30

seconds i n o r d e r t o avoid temporal a f f e c t s i n f l u e n c i n g t h e sub-

j e c t ' s responses .

One of t h e two obse rva t ion d i s t a n c e s (75 and 270 f e e t ) , a s

measured from t h e board c a r r y i n g t h e t e s t lamps t o t h e approxi-

mate l o c a t i o n of t h e eyes of t h e o b s e r v e r s , was randomly s e l e c -

t ed . T e s t s were then conducted u s i n g one of t h e c o l o r s , ran-

domly s e l e c t e d , wi th a l l t h e lamp a r e a s and t h e two lamp loca-

t i o n s randomly ordered . The c o l o r of t h e lamps was then changed

and t h e procedure r e p e a t e d u n t i l a l l a r e a s and l o c a t i o n s had been

p resen ted . When a l l t h e c o l o r s had been shown t o t h e obse rve rs

a t one o b s e r v a t i o n d i s t a n c e t h e t e s t was repea ted , aga in random-

i z i n g c o l o r s and a r e a s w i t h i n c o l o r s , a t t h e o t h e r obse rva t ion

d i s t a n c e .

P r i o r t o commencing t h e t e s t s e s s i o n s a number of p r a c t i c e

t r i a l s were given t o f a m i l i a r i z e t h e obse rve rs wi th t h e procedure.

A t t h e end of an exper imenta l s e s s i o n t h e s u b j e c t s were asked

t o d e s c r i b e t h e c r i t e r i a t h a t they had used i n responding t o t h e

l i g h t . This was done i n o r d e r t o o b t a i n some f u r t h e r i n s i g h t i n t o

60

t h e i n t e r p r e t a t i o n t h a t t h e s u b j e c t s p laced upon t h e i n s t r u c -

t i o n s .

During daytime s e s s i o n s t h e luminance of t h e board s u r -

rounding t h e t e s t lamps was measured wi th t h e P r i t c h a r d photo-

meter whenever c o l o r f i l t e r s were changed, ~ p p r o x i m a t e l y 28%

of day t e s t s were c a r r i e d o u t w i t h t h e lamp surround a t a lumi-

nance of up t o 1250 f t / l , 56% a t 1250-2500 f t / l , and 16% a t

2500-3750 f t / l . During n igh t t ime s e s s i o n s t h e low-beam head-

l i g h t s of t h e v e h i c l e i n which t h e s u b j e c t s were s e a t e d were

tu rned on t o s imula te a roadway i l l u m i n a t i o n found i n r u r a l

n i g h t d r i v i n g . There was a ve ry low ambient l i g h t l e v e l from

d i s t a n t s t r e e t lamps and b u i l d i n g s .

R e s u l t s . The responses of t h e s u b j e c t s were i n t h e form

of r e c o r d s made on t h e s t r i p c h a r t paper i n d i c a t i n g t h e v o l t a g e

i n p u t l e v e l s t o t h e lamps a t which o b s e r v e r s made c r i t e r i o n

responses . The v o l t a g e read ings a t which t h e responses occurred

were read from t h e s t r i p c h a r t o u t p u t .

For each lamp a r e a and c o l o r , photometr ic d a t a i n candle-

power were taken and c o r r e l a t e d wi th t h e v o l t a g e i n p u t t o t h e

lamp. The voltage-candlepower c a l i b r a t i o n s were then r e a d i n t o

a computer. The v o l t a g e read ings i n d i c a t i n g t h e s u b j e c t s '

responses were p laced on computer i n p u t c a r d s f o r conversion

i n t o candlepower v a l u e s by t h e computer from t h e photometr ic

c a l i b r a t i o n s , and subsequen t ly f o r d a t a a n a l y s i s .

For each viewing d i s t a n c e and ambient c o n d i t i o n , lamp a r e a ,

c o l o r and l o c a t i o n , and c o l o r v i s i o n of t h e o b s e r v e r s , a cumula-

t i v e pe rcen tage d i s t r i b u t i o n t a b l e was produced f o r t h e f i v e

lamp a r e a s and t h e h igh mounted l o c a t i o n ,

From t h e cumulat ive p e r c e n t i l e t a b l e s ob ta ined f o r each

t e s t c o n d i t i o n two cu t -o f f v a l u e s were s e l e c t e d by which t h e

daytime and n i g h t t i m e c r i t e r i a w i l l be judged. I n t h e daytime

t h e 85th p e r c e n t i l e candlepower v a l u e s were taken and a r e i n t e r -

p r e t e d t o be those v a l u e s i n which t h e s i g n a l i n t e n s i t y can be

cons ide red t o ba a maximum requirement . This i s because t h e s e

d a t a were taken under very b r i g h t day cond i t ions f o r t h e most

p a r t , and because t h e i n s t r u c t i o n s given t o t h e s u b j e c t s were n o t merely t o s t r e s s adequate v i s i b i l i t y b u t t o i n d i c a t e when

t h e l i g h t s were d e f i n i t e l y of adequate b r i g h t n e s s t o be seen a s

a s i g n a l . For t h e s e reasons it was expected t h a t h igher va lues

would be ob ta ined than those r e p o r t e d i n previous experiments .

The daytime v a l u e s , p a r t i c u l a r l y when taken a t a high p e r c e n t i l e

va lue , such a s t h e 85th p e r c e n t i l e , a r e maximum requirements which

need n o t be exceeded f o r a h i g h l y v i s i b l e s i g n a l , On t h e o t h e r

hand, t h e n igh t t ime d a t a a r e considered t o be candlepower va lues

which would be i n t o l e r a b l e because of t h e e x t e n t of d iscomfor t

and d i s a b i l i t y g l a r e t h a t they would cause. For t h e s e reasons a low p e r c e n t i l e va lue of candlepowere judged i n t o l e r a b l e was s e l e c -

t e d , namely t h e 15 th p e r c e n t i l e , and t h e s e va lues a r e cons idered

t o be maximum va lues f o r r e a r l i g h t i n g system s i g n a l s when viewed

under n igh t t ime cond i t ions .

Table 2 . 1 shows t h e 85th p e r c e n t i l e candlepower va lues and

a l s o t h e convers ions of t h e s e va lues i n t o candles per square inch

based upon the luminous a r e a of t h e t e s t lamp i n each cond i t ion .

The values a r e shown a s a func t ion of luminous a r e a , viewing d i s - 6

t a n c e , and lamp c o l o r , f o r s u b j e c t s having normal c o l o r v i s i o n .

The analogous d a t a , 85th p e r c e n t i l e maximum daytime v a l u e s , f o r

co lo r -b l ind observers a r e shown i n Table 2 . 2 .

The values t h a t were obta ined a r e a func t ion of t h e lamp

a r e a and t h e c o l o r of t h e l i g h t . The a r e a l a b e l e d 1 2 . 6 H r e f e r s

t o t h e $-inch d iameter lamp i n t h e h igher l o c a t i o n and i s i n s e r -

t e d f o r comparison wi th t h e lamp of t h e same a r e a , 12.6 square

i n c h e s , which was l o c a t e d c l o s e r t o ground l e v e l . The e f f e c t of

t h e viewing d i s t a n c e can be seen t o be smal l i n a f f e c t i n g t h e day-

t ime va lues . I t w i l l a l s o be noted t h a t t h e va lues f o r candle-

power maximum requirements a r e q u i t e high. For example, a lamp

having an area of 1 2 . 6 square inches (approximately Class-A) i n

r e d was considered adequate, us ing t h e c r i t e r i o n a l ready d i scussed ,

TABLE 2 . 1 . 8 5 t h PERCENTILE INTENSITY AND LUMINANCE VALUES JUDGED ADEQUATE BY 3 7 COLOR-NORMAL SUBJECTS FOR EACH COLOR, LAMP AREA, AND VIEWING DISTANCE IN THE DAY

CANDLES

75 feet 2 7 0 feet

Area (sq. inches)

4 . 0

6 . 1

1 2 . 6

2 5 . 2

3 7 . 8

1 2 . 6H

W

5 ,613

1 2 , 8 8 0

1 3 , 2 8 7

2 1 , 4 4 0

1 8 , 9 1 6

1 5 , 0 9 6

CANDLES/SQ. INCH

R

9 1 4

1 , 5 5 3

2 , 1 4 1

4 , 2 9 7

4 , 1 1 1

2 , 5 3 8

4 .0

6 . 1

1 2 . 6

2 5 . 2

3 7 . 8

1 2 . 6H

A

2 , 9 4 4

5 , 2 4 3

7 , 9 2 8

9 , 7 9 2

1 2 , 6 1 1

5 , 3 2 6

1 4 0 3 . 3

2 1 1 1 . 5

1 0 5 4 . 5

8 5 0 . 8

5 0 0 . 4

1 1 9 8 . 1

G

1 , 0 1 0

1 , 6 6 6

2 , 0 2 4

3 , 9 2 3

2 , 6 4 5

2 , 4 3 7

2 2 8 . 5

2 5 4 . 6

1 6 9 . 9

1 7 0 . 5

1 8 0 . 8

2 0 1 . 4

W

5 , 6 3 8

9 , 5 5 5

1 6 , 7 0 9

1 9 , 0 5 0

1 8 , 9 5 7

7 3 6 . 0

8 6 0 . 0

6 2 9 . 2

3 8 8 . 6

3 3 3 . 6

4 2 2 . 7

I

R

1 , 0 2 9

2 , 0 7 9

2 , 5 7 0

4 , 6 0 1

3 , 7 9 1

2 5 2 . 5

2 7 3 . 1

1 6 0 . 6

1 5 5 . 7

7 0 . 0

1 9 3 . 4

1 2 , 5 2 7

A

2 , 7 3 8

4 , 8 9 3

7 , 0 2 5

1 0 , 5 8 4

8 , 9 8 2

0 , 0 5 5

G

1 , 2 4 8

2 , 0 8 0

2 , 4 5 3

3 , 4 5 0

3 , 5 5 2

1 4 0 9 . 5

1 5 6 6 . 4

1 3 2 6 . 1

7 5 6 . 0

5 0 1 . 5

9 9 4 . 2

6 8 4 . 5

8 0 2 . 1

5 5 7 . 5

4 2 0 . 0

2 3 7 . 6

4 7 0 . 7

2 5 7 . 3

3 4 0 . 8

2 0 4 . 0

1 8 2 . 6

1 0 0 . 3

2 4 2 . 5

5 , 9 3 1

3 1 2 . 0

3 4 1 . 0

1 9 4 . 7

1 3 6 . 9

9 4 . 0

1 6 5 . 3

2 , 0 8 3

TABLE 2 . 2 . 8 5 t h PERCENTILE INTENSITY AND LUMINANCE VALUES JUDGED ADEQUATE BY 1 0 COLOR-BLIND SUBJECTS FOR EACH COLOR, LAMP AREA, AND VIEWING DISTANCE I N THE DAY

CANDLE S

7 5 f ee t 2 7 0 f ee t

A r e a (sq. i n c h e s )

4 . 0

6 . 1

1 2 . 6

2 5 . 2

3 7 . 8

1 2 . 6H

2 , 9 4 0

7 , 4 7 6

7 , 9 4 2

2 5 , 0 6 7

1 1 , 4 8 5

1 1 , 9 5 2

R

442

1 , 2 8 7

2 , 3 0 7

4 , 9 6 1

3 , 1 6 9

2 , 4 8 3

A

1 , 5 3 5

3 , 7 0 9

5 , 2 5 9

1 1 , 9 5 1

9 , 0 2 1

4 , 4 4 8

W

3 , 5 7 4

5 , 9 0 0

1 0 , 4 0 0

1 9 , 0 5 0

2 0 , 6 1 1

1 5 , 1 5 0

L

G

5 2 6

1 , 0 8 9

1 , 5 5 7

2 , 5 2 4

2 , 4 0 6

1 , 4 9 5

R

8 4 5

1 , 6 0 0

1 , 6 2 1

4 , 1 6 8

3 , 5 0 0

2 , 3 4 3

A

1 , 6 8 2

4 , 9 0 0

4 , 9 8 8

7 , 7 6 7

6 , 8 8 8

5 , 5 4 4

G

5 1 5

1 , 1 4 7

1 , 9 7 2

2 , 6 6 6

2 , 2 2 5

1 , 5 4 9

a t o v e r 2000 candlepower i n t h e s e tes t s . Also q u i t e e v i d e n t

from t h e t a b l e s i s t h e f a c t t h a t d i f f e r e n t c o l o r s r e q u i r e d d i f -

f e r e n t candlepower v a l u e s t o be judged e q u i v a l e n t i n b r i g h t n e s s

acco rd ing t o t h e c r i t e r i o n a s it was i n t e r p r e t e d by o u r t e s t

s u b j e c t s . For example, a w h i t e s i g n a l of 12 .6 s q u a r e i n c h e s a t

t h e 75-foot v iewing d i s t a n c e f o r t h e normal s u b j e c t s r e q u i r e s

13,287 candlepower a t t h e 85 th p e r c e n t i l e v a l u e , compared t o 2141,

7928, and 2024 candlepower f o r r e d , amber and g r e e n .

The e f f e c t of lamp a r e a was t a k e n i n t o accoun t by c o n v e r t i n g

t h e candlepower v a l u e s shown a s t h e upper d a t a s e t i n t h e s e two

t a b l e s t o luminance v a l u e s i n c a n d l e s p e r s q u a r e i n c h by d i v i d -

i n g t h e candlepower v a l u e s by t h e r e s p e c t i v e lamp a r e a , Th i s

w i l l h e l p t o show t h e r o l e p layed by lamp a r e a i n d e t e r m i n i n g

t h e s u b j e c t s ' b r i g h t n e s s judgments, I t w i l l be n o t e d t h a t , on

t h e b a s i s of luminance, s m a l l a r e a s o u r c e s g e n e r a l l y r e q u i r e

h i g h e r i n t e n s i t i e s p e r u n i t a r e a t h a n l a r g e s o u r c e s , e x c e p t f o r

an i n v e r s i o n which h a s been found i n t h e s e d a t a i n most compari-

sons f o r t h e 4-square i n c h lamp which r e q u i r e d less i n t e n s i t y p e r

u n i t a r e a t h a n a lamp of 6 s q u a r e i n c h e s . Whether t h i s s u g g e s t s

an a r t i f a c t i n t h e d a t a i s d i f f i c u l t t o know a t t h i s time, b u t

it shou ld be n o t e d t h a t t h e t e s t lamps used had a c i r c u l a r s h i e l d

i n f r o n t of t h e f i l a m e n t such t h a t t h e r e was, i n f a c t , a reduc-

t i o n i n t h e e f f e c t i v e luminous a r e a which would have been a l a r g e r

p r o p o r t i o n of t h e a r e a of t h e s m a l l d i a m e t e r s o u r c e s t h a n i n t h e

l a r g e r ones . Whether t h i s was a r e a l e f f e c t o r n o t i s unknown

now, b u t it shou ld be p o i n t e d o u t t h a t t h e f i l a m e n t s h i e l d was

n o t n o t i c e a b l e a t t h e h i g h lamp i n t e n s i t i e s r e q u i r e d t o o b t a i n

r e sponses . I f an ad jus tmen t was made f o r t h e e f f e c t i v e lumi-

nous a r e a by s u b t r a c t i n g t h e a r e a of t h e f i l a m e n t s h i e l d from t h a t

of t h e a p e r t u r e t h e n a d e c r e a s e i n luminous i n t e n s i t y w i t h lumi-

nous a r e a would g e n e r a l l y have been o b t a i n e d . The d a t a a s shown

i n t h e t a b l e s do n o t r e f l e c t such a m o d i f i c a t i o n .

Tab le s 2 .3 and 2 . 4 show t h e 1 5 t h p e r c e n t i l e candlepower and

TABLE 2.3. 15th PERCENTILE INTENSITY AND LUMINANCE VALUES JUDGED INTOLERABLE BY 32 COLOR-NORMAL SUBJECTS FOR EACH COLOR, LAMP AREA, AND VIEWING DISTANCE AT NIGHT

CANDLES

270 feet

CANDLES/SQ. INCH

TABLE 2.4. 1 5 t h PERCENTILE INTENSITY AND LUMINANCE VALUES JUDGED INTOLERABLE BY 8 COLOR-BLIND SUBJECTS FOR EACH COLOR, LAMP AREA, AND VIEWING DISTANCE AT NIGHT

CANDLES

75 f e e t 270 f ee t

CANDLES/SQ. INCH

G

3 1

8 1

6 4

1 3 3

236

70

A

1 0 3

1 2 4

99

140

192

1 6 1

Area (sq. inches)

4.0

6 . 1

1 2 . 6

25 .2

37 .8

1 2 . 6H

W

274

239

557

594

667

1 , 0 4 1

W

1 1 2

217

1 6 2

376

485

260

R

111

1 5 1

393

367

357

1 4 1

G

70

102

260

319

288

R I A

2 0 1

483

397

546

407

79

387

142

589

385

260 1 3 1 I 3 2 7

cand les p e r squa re inch v a l u e s t h a t were judged i n t o l e r a b l e f o r

normal and c o l o r - b l i n d s u b j e c t s r e s p e c t i v e l y . The t a b l e s a r e

based upon lamp a r e a , viewing d i s t a n c e , and c o l o r f o r t h e same

v a r i a b l e s a s shown i n t h e t a b l e s of daytime r e s u l t s ,

I t w i l l be no ted t h a t t h e i n t o l e r a b l e n i g h t t i m e v a l u e s a r e

cons ide rab ly below 85th p e r c e n t i l e daytime v a l u e s and t h a t t h e r e

a r e , a g a i n , d i f f e r e n c e s due t o lamp a r e a , c o l o r , and viewing

d i s t a n c e . The v a l u e s shown i n Table 2.3 can be taken a s maxi-

mum n i g h t t i m e v a l u e s f o r s u b j e c t s having normal v i s i o n , f o r t h e

i n d i c a t e d lamp a r e a s and c o l o r s .

I n o r d e r t o b e t t e r show t h e e f f e c t of t h e independent v a r i -

a b l e s used i n t h i s t e s t a number of computat ions were made on t h e

luminance v a l u e s shown i n Tables 2 . 1 - 2 . 4 . Table 2.5 shows lumi-

nance r a t i o s which a r e d e f i n e d a s t h e r e l a t i v e luminance of a

color-ambient.illumination-color v i s i o n combination i n each d i s -

t a n c e t o t h e e q u i v a l e n t c o n d i t i o n i n r e d , summed over t h e lamp

a r e a s . For example, Table 2.5 shows t h a t a wh i t e l i g h t viewed

a t 75 f e e t i n t h e daytime by o b s e r v e r s w i th normal c o l o r v i s i o n

r e q u i r e s 6.28 times more i n t e n s i t y p e r u n i t luminous a r e a than

an e q u i v a l e n t r e d source . S i m i l a r l y , amber and green-blue r e q u i r e

2.97 and 0.97 t imes more luminous i n t e n s i t y t h a n an e q u i v a l e n t r e d

lamp. These d a t a i n d i c a t e t h e r a t i o of i n t e n s i t i e s r e q u i r e d t o

ach ieve t h e same s u b j e c t i v e c r i t e r i o n f o r v a r i o u s c o l o r s , i nc lud -

i n g w h i t e , when viewed by normal and c o l o r - b l i n d i n d i v i d u a l s i n

daytime. The n i g h t t i m e d a t a i n t h i s t a b l e a r e t h o s e u s i n g t h e

i n t o l e r a b l e g l a r e d i scomfor t c r i t e r i o n and a r e based on t h e 1 5 t h

p e r c e n t i l e v a l u e s t h a t were shown i n Tables 2.3 and 2 . 4 . For

example, Table 2.5 shows t h a t a t 75 f e e t a wh i t e l i g h t may have

2.66 t imes t h e luminous i n t e n s i t y of an analogous r e d l i g h t f o r

e q u a l d i scomfor t when viewed by normal o b s e r v e r s . The d a t a a l s o

show t h a t c o l o r - b l i n d and normal o b s e r v e r s do n o t have t h e same

re sponse f o r s u b j e c t i v e g l a r e d i scomfor t a c r o s s t h e d i f f e r e n t c o l o r s

a s i s r e v e a l e d by t h e r e l a t i v e luminous i n t e n s i t i e s shown i n Table

2.5. For example, normal obse rve rs w i l l t o l e r a t e a h igher r a t i o

of white t o r e d (2.66:100) compared t o co lo r -b l ind obse rve rs

(1 ,05 :1 .00) . Also, t h e r e appears t o be a d i f f e r e n t response t o

amber i n which co lo r -b l ind observers can t o l e r a t e l e s s i n t e n s i t y

i n amber than r e d , whereas normal obse rve rs found amber of equiva-

l e n t candlepower l e s s g l a r i n g than red .

S ince t h e r a t i o s t h a t a r e shown i n Table 2.5 a r e s i m i l a r a t

t h e 75 f o o t and 270 f o o t d i s t a n c e s , t h e d a t a were co l l apsed over

d i s t a n c e and a r e presented i n t h a t form i n Table 2.6, Table 2 . 6

shows more c l e a r l y t h e i n t e n s i t y r a t i o r e q u i r e d f o r e q u i v a l e n t

c r i t e r i o n s u b j e c t i v e responses i n t h e day and n i g h t c o n d i t i o n s ,

f o r normal and co lo r -b l ind obse rve rs , The mean day r e s u l t s , which

a r e t h e means f o r both normal and co lo r -b l ind s u b j e c t s , provide

r a t i o s f o r whi te , r e d , amber, and green-blue of 5.28, 1 . 0 0 , 2 .58,

and 0.85. These va lues i n d i c a t e t h e r e l a t i v e i n t e n s i t i e s f o r

t h e s e c o l o r s t o be cons idered s u b j e c t i v e l y equal by t h e t e s t

c r i t e r i a when t h e lamp a r e a i s ignored, This seems t o be a

reasonable approach, s i n c e Tables 2 . 1 and 2 . 2 d i d n o t i n d i c a t e

an i n t e r a c t i v e a f f e c t of lamp a r e a and c o l o r , The r e l a t i v e i n t e n -

s i t i e s f o r e q u a l c r i t e r i o n response i n t h e daytime t h a t a r e shown

i n t h e upper p o r t i o n of Table 2.6 a r e very c l o s e t o t h e r a t i o s

t h a t a r e sugges ted i n SAE J575A ( 1 9 6 7 ) f o r t h e minimum candlepower

r a t i o s a t t h e H-V p o i n t f o r r e d , amber, and whi te l i g h t s . Those

r a t i o s a r e 1 :2 .5 :5 ,0 , and a r e t h e r e f o r e almost p r e c i s e l y those

ob ta ined i n t h e s e t e s t s (1 :2 .58:5 ,28) , These r e s u l t s a l s o show

va lues f o r green-blue which have n o t been p rev ious ly repor ted

and i n d i c a t e t h a t green-blue r e q u i r e s a lower i n t e n s i t y than red

f o r e q u i v a l e n t v i s i b i l i t y i n daytime, The o v e r a l l r a t i o obta ined

i n t h i s t e s t f o r normal and co lo r -b l ind obse rve rs was 0.85 when

compared t o r ed .

Table 2.6 a l s o shows t h e luminance r a t i o s f o r t h e n igh t t ime

d a t a . I t w i l l be noted t h a t t h e s e r a t i o s vary between normal and

co lo r -b l ind obse rve rs more than t h e comparable daytime r a t i o s .

TABLE 2.5. LUMINANCE RATIOS* FOR COLORS (AND WHITE), DISTANCE, NORMAL AND COLOR BLIND SUBJECTS, DAY AND NIGHT

CANDLES

75 feet 270 feet

*Luminance ratio is the criterion luminance for a color/ criterion luminance for red

TABLE 2.6. MEAN LUMINANCE RATIOS* FOR COLORS, AND FOR NORMAL AND COLOR-BLIND SUBJECTS, OVER VIEWING DISTANCE

Green- White Red Amber Blue

MEAN DAY

MEAN NIGHT 1.86 1.00 1.22 ' [LcNIGHT]

*Luminance ratio is the criterion luminance for a color/ criterion luminance for red

[L~/~RE o ) ( ) Values in parentheses are the number of subjects in

that condition 70

Thi s i n d i c a t e s t h a t c o l o r - b l i n d o b s e r v e r s and normal s u b j e c t s

have a d i f f e r e n t i a l r e s p o n s e t o g l a r e d i s c o m f o r t and t h a t t h i s

i s d i f f e r e n t a c c o r d i n g t o t h e c o l o r of t h e l i g h t . I n a d d i t i o n ,

it w i l l be n o t i c e d t h a t g reen-b lue i n t e n s i t i e s a r e app rox ima te ly

h a l f of t h o s e t h a t c o u l d be used f o r r e d f o r e q u a l d i s c o m f o r t

judgment. The o v e r a l l mean n i g h t luminance r a t i o s summed o v e r

t h e normal and c o l o r - b l i n d s u b j e c t s , appea r i n Tab le 2.6 and show

t h e i n t e n s i t y r a t i o s f o r e q u a l g l a r e d i s c o m f o r t o v e r sys tems a t

n i g h t .

The r e l a t i v e e f f e c t o f lamp a r e a upon i n t e n s i t y r e q u i r e m e n t s

i s shown i n Tab le 2 . 7 , which compares t h e luminance r a t i o s f o r

e a c h lamp a r e a , ambient c o n d i t i o n , and f o r normal and c o l o r - b l i n d

s u b j e c t s . These d a t a a r e averaged a c r o s s t h e lamp c o l o r and di;-

t a n c e . I t w i l l be n o t e d t h a t t h e t a b l e h a s been s o s t r u c t u r e d

t h a t luminance r a t i o s a r e t a k e n w i t h r e s p e c t t o t h e 12 .6-square-

i n c h lamp. I n t e n s i t y p e r u n i t a r e a d e c r e a s e s w i t h i n c r e a s i n g

lamp a r e a f o r t h e dayt ime and n i g h t t i m e c r i t e r i a . The r e s u l t s

f o r t h e lamp 1 2 , 6 H , which was mounted a t a b o u t d r i v e r eye h e i g h t ,

showed t h a t it r e q u i r e d less mean i n t e n s i t y t h a n t h e e q u i v a l e n t

lamp mounted a t 2 4 i n c h e s f o r normal s u b j e c t s b u t g r e a t e r i n t e n -

s i t y f o r c o l o r - b l i n d s u b j e c t s . S i n c e t h e o v e r a l l t r e n d s a r e

s i m i l a r f o r t h e day and t h e n i g h t c r i t e r i o n t h e v a l u e s were com-

b i n e d t o form o v e r a l l means t o show t h e e f f e c t o f lamp a r e a upon

i n t e n s i t y r e q u i r e m e n t s . The d a t a f o r normal s u b j e c t s o n l y were

used i n t h e s e means because o f t h e g r e a t e r r e l i a b i l i t y of t h e i r

d a t a . The d a t a i n d i c a t e t h a t a lamp of 6 .1 s q u a r e i n c h e s r e q u i r e s

1 . 6 1 times t h e i n t e n s i t y of a lamp of abou t twice t h e a r e a , 12.6

s q u a r e i n c h e s , and t h a t t h e s e r e s u l t s h o l d i r r e s p e c t i v e of c o l o r

and the c r i t e r i o n r e s p o n s e , i . e , adequacy i n day o r d i s c o m f o r t

a t n i g h t . These d a t a a r e u s e f u l i n d e t e r m i n i n g t h e r e l a t i v e

i n t e n s i t y r e q u i r e m e n t s f o r day and n i g h t v iewing c o n d i t i o n s f o r

lamps o f v a r i o u s a r e a s and a r e shown i n t h e form of a p l o t i n

F i g u r e 2.4.

TABLE 2.7. LUMINANCE RATIO* AS A FUNCTION OF LAMP A m A ACROSS COLOR AND DISTANCE FOR NORMAL AND COLOR-BLIND SUBJECTS FOR DAY AND NIGHT CRITERIA

Area (sq. inches)

-

*Luminance ratio is the criterion luminance for an area/ criterion luminance for 12.6 in2

TABLE 2.8. THE EFFECTS OF VIEWING DISTANCE UPON DAY (85th PERCENTILE) AND NIGHT (15th PERCENTILE) LUMINANCE RATIOS* FOR NORMAL AND COLOR-BLIND SUBJECTS

Luminance Ratio

37.8

.45

.55

. 4 5

.48

.45

25.2

.71

1.08

.60

,74

-66

12.6*

.90

1.25

.83

1.15

.84

Day-N

Day-CB

Night-N

Night-CB

MEAN NORMAL

*Luminance ratios are based on mean luminance values by combining data over color and areas in each distance: 270 feet and 75 feet.

6.1

1.52

1.55

1.70

1.76

1.61

4.0

1.23

1.05

1.20

1.49

(1.22)

L 270 feet/L 75 feet - Day-N .97

Day-CB 1.06

Night-N 1.56

Night-CB 2.00

12.6

1.00

1,OO

1.00

1.00

1.00

Mean

1.02

1.78

0 1 0 2 0 3 0 40

LUMINOUS AREA (SQ. INCHES)

F i g u r e 2 .4 . Luminance r a t i o f o r d a y a n d n i g h t i n t e n s i t i e s a s a f u n c t i o n o f a r e a .

73

I t has been recognized , i n s t u d i e s conducted by t h e Automobile

Manufacturers A s s o c i a t i o n (1964, 1 9 6 5 ) , t h a t lamps having a r e a

r a t i o s of 1:2:3 shou ld have approximate i n t e n s i t y r a t i o s of 1:0.6:

0.5. The p r e s e n t d a t a ex tend t h e s e f i n d i n g s and p rov ide recom-

mendations which may be d i r e c t l y a p p l i e d t o lamp i n t e n s i t y r e q u i r e -

ments a s a f u n c t i o n of lamp a r e a and l o c a t i o n . The results f o r

t h e 4 squa re inch a r e a should be regarded w i t h c a u t i o n because

they may be due t o t h e a r t i f a c t t h a t has a l r e a d y bwen mentioned.

I t seems more probable t h a t a lamp 4 squa re i n c h e s i n a r e a w i l l

r e q u i r e a h i g h e r luminous i n t e n s i t y t h a n l a r g e r lamps a s i n d i -

c a t e d by F igu re 2 . 4 i n which t h e broken l i n e ex tend ing t h e curve

shows t h e l i k e l y t r e n d .

Table 2.8 shows t h e luminance r a t i o s , a s a f u n c t i o n of t h e

ambient i l l u m i n a t i o n and t h e c o l o r v i s i o n of t h e d r i v e r , f o r t h e

two d i s t a n c e s used i n t h e t e s t (75 and 270 f e e t ) . I t w i l l be

no ted t h a t i n daytime c o n d i t i o n s t h e r e i s l i t t l e e f f e c t upon t h e

c r i t e r i o n judgments due t o t h e viewing d i s t a n c e . However, a t

n i g h t t h e r e i s a d i f f e r e n t i a l response due t o t h e d i s t a n c e which

i n d i c a t e s t h a t a s t h e d i s t a n c e i s reduced luminous i n t e n s i t i e s

must a l s o be reduced f o r t h e same g l a r e d i scomfor t . The o v e r a l l

mean luminance r a t i o s f o r d i s t a n c e i n day and n i g h t c o n d i t i o n s ,

f o r color-normal and c o l o r - b l i n d o b s e r v e r s , a r e 1.02 and 1.78.

These f i n d i n g s i n d i c a t e t h a t daytime i n t e n s i t i e s need n o t

t a k e i n t o account t h e viewing d i s t a n c e , w i t h i n t h e range inves -

t i g a t e d i n t h e s e t e s t s , b u t t h a t n i g h t g l a r e v a l u e s were a f f e c -

t e d by t h e d i s t a n c e and f o r t h i s r eason t h e 75-foot v a l u e s

should be used.

On t h e b a s i s of t h e o v e r a l l test r e s u l t s it i s p o s s i b l e t o

make recommendations f o r daytime and n i g h t t i m e i n t e n s i t y r e q u i r e -

ments. Daytime requi rements should be based on t h e f i n d i n g s

r e p o r t e d i n Table 2.9 which were o b t a i n e d by t a k i n g t h e mean v a l u e

f o r 75 and 275 f e e t of each cor responding c e l l i n Table 2 . 1 .

Table 2.9 shows, t h e r e f o r e , t h e mean 85th p e r c e n t i l e daytime

TABLE 2 .9 . MEAN 8 5 t h PERCENTILE DAYTIME CP VALUES OBTAINED FROM TABLE 2 . 1 BY AVERAGING OVER DISTANCE

C o l o r

TABLE 2 . 1 0 . 5 0 t h PERCENTILE CANDLEPOWER VALUES FOR DUSK/DAWN SIMULATION, DAY AND NIGHT OUTDOOR TESTS, FOR RED AND GREEN-BLUE, AND THREE AREAS, AT 7 5 FEET

A r e a (sq, i n c h e s )

A r e a ( s q . i n c h e s )

4 . 0

6 . 1

1 2 . 6

' 2 5 . 2

3 7 . 8

1 2 . 6 H

Red G r e e n - B l u e

W

5 , 6 2 6

1 1 , 2 1 8

1 4 , 9 9 8

2 0 , 2 4 5

1 8 , 9 3 7

1 3 , 8 1 2

R

9 7 2

1 , 8 1 6

2 , 3 5 6

4 , 4 4 9

3 , 9 5 1

2 , 7 9 7

A

2 , 8 4 1

5 , 0 6 8

7 , 4 7 7

1 0 , 1 8 8

1 0 , 7 9 7

5 , 6 2 9

C o n d i t i o n

Dusk/Dawn- I n t o l e r a b l e (N=15)

Day -Adequa t e (N=37)

N i g h t - I n t o l e r a b l e (N=32)

G r e e n - B l u e

1 , 1 2 7

1 , 8 7 3

2 , 2 3 9

3 , 6 8 7

3 , 0 9 9

2 , 2 6 0

4 .0

3 2 0

3 9 1

336

3 7 . 8

1 , 3 3 4

1 , 5 4 9

1 , 5 0 2

1 2 . 6

767

1 , 0 1 6

956

4 . 0

2 0 3

3 9 8

260

1 2 . 6

423

854

6 2 8

3 7 . 8

5 3 6

9 3 7

676

"adequacy" d a t a averaged over d i s t a n c e , and t h e v a l u e s should be

i n t e r p r e t e d a s t h e mean upper limits f o r each c o l o r combinat ion,

o m i t t i n g t h e 4-square-inch a r e a and c o n f i n i n g t h e recommendations

t o lamps having a r e a s between 6 square inches and 37 .8 square

inches . For example, it would be recommended t h a t a r e d s i g n a l

l i g h t of 12,6 square inches have a maximum i n t e n s i t y of about

2536 c p , whereas a lamp of 3 7 . 8 square inches should have a maxi-

mum i n t e n s i t y of about 3952 cp. These d a t a i n d i c a t e maximum v a l u e s ,

b u t i t w i l l be necessa ry t o s p e c i f y t h e a p p r o p r i a t e i n t e n s i t y

range f o r t h e daytime c o n d i t i o n , This means t h a t minimum v a l u e s

a r e s t i l l needed. Minimum i n t e n s i t y requi rements can be ob ta ined

by measurement of v a l u e s i n which g l a r e d iscomfor t occur under

dusk/dawn c o n d i t i o n s , s i n c e t h e s e a r e cons idered t h e lowest ambient

daytime c o n d i t i o n s b e f o r e h e a d l i g h t s w i l l be used.

Measurements made by Ki lgour (1962) i n D e t r o i t , i n August

1960, show t h a t ambient i l l u m i n a t i o n a t sundown was about 30

foo t -cand les and t h a t h e a d l i g h t s were f i r s t n o t i c e d a t about 2 0

foo t -cand les . Half t h e v e h i c l e s used h e a d l i g h t s a t 1 2 f o o t -

cand les and a lmost a l l a t 8 foo t -cand les . This means t h a t most

d r i v e r s were us ing h e a d l i g h t s w e l l b e f o r e da rkness , a t dusk.

The d a t a a l s o showed t h a t t h e r e was a t ime d i f f e r e n c e of about

17 minutes between t h e time t h a t t h e f i r s t c a r and a l l c a r s used

h e a d l i g h t s . Another s tudy (Allen & Clark , 1964) showed t h a t

h e a d l i g h t s were f i r s t used a t about 25 foo t -cand les , wi th 50

p e r c e n t use a t 15 foo t -cand les on a c l e a r day, Within 30 minutes

almost a l l v e h i c l e s were us ing h e a d l i g h t s . Under an o v e r c a s t sky

t h e same i n v e s t i g a t o r s found t h a t h e a d l i g h t s were tu rned on much

sooner . For example, 80 p e r c e n t of v e h i c l e s used h e a d l i g h t s i n

15 foo t -cand les .

The r e s u l t s of t h e s e s t u d i e s show t h a t w i t h i n a pe r iod of

about 2 0 minutes a t dusk most v e h i c l e s w i l l have gone through

a t r a n s i t i o n of head l igh t s -o f f t o head l igh t s -on , and t h a t 50

p e r c e n t of v e h i c l e s w i l l use h e a d l i g h t s a t 1 0 foo t -cand les i l l u -

minat ion o r g r e a t e r .

I t , t h e r e f o r e , would seem a p p r o p r i a t e t o recommend t h a t

minimum daytime s i g n a l i n t e n s i t i e s ( h e a d l i g h t s - o f f ) should be

t h o s e t h a t a r e a t t h e t h r e s h o l d of d i scomfor t g l a r e f o r about

25 p e r c e n t of d r i v e r s a t dusk/dawn ( 4 0 foo t -cand les o r below)

ambient i l l u m i n a t i o n . I n t h i s way most d r i v e r s a r e n o t caused

d i scomfor t and t h e remainder a r e l i k e l y t o be a f f e c t e d only f o r

a s h o r t t ime pe r iod of about 1 0 minutes o r l e s s . The same would

probably be t r u e a t dawn. S e l e c t i o n of such a c r i t e r i o n does

mean, however, t h a t daytime minimum v a l u e s may n o t be adequate

f o r about 75 p e r c e n t of d r i v e r s i n b r i g h t , day c o n d i t i o n s , accord-

i n g t o t h e c r i t e r i o n used i n t h e day t e s t .

DUSK/DAWN SIMULATION DISCOMFORT INTENSITY TEST. I n o r d e r

t o o b t a i n d i scomfor t i n t e n s i t y va lues i n dusk/dawn c o n d i t i o n s a

t e s t was c a r r i e d o u t indoors i n which t h e i l l u m i n a t i o n c o n d i t i o n s

could be c o n t r o l l e d .

Method. The same t e s t lamps, r ecord ing equipment and pro-

cedure were used a s i n t h e outdoor s t u d i e s . Viewing d i s t a n c e

was 75 f e e t . Three lamp a r e a s , 4 . 0 , 1 2 . 6 and 37.8 square i n c h e s ,

i n r ed and green-blue were used. The ceiling-mounted f l u o r e s -

c e n t lamps provided a uniform i l l u m i n a t i o n of 4 0 foot -candles on

t h e f l o o r , and t h e t e s t lamp surround board luminance was 13 f t / l .

Three s u b j e c t s were used i n t h e s e t e s t s who rece ived 5

ascending-descending t r i a l s i n each c o n d i t i o n , They were read

t h e same i n s t r u c t i o n s a s t h o s e used i n t h e n i g h t , outdoor t e s t

(Appendix A-1) . R e s u l t s . The 50th p e r c e n t i l e d iscomfor t ( i n t o l e r a b l e ) i n t e n -

s i t y v a l u e s a r e shown i n Table 2 . 1 0 . Also shown a r e t h e 50th per-

c e n t i l e day adequacy and n i g h t i n t o l e r a b l e v a l u e s ob ta ined i n t h e

outdoor t e s t s . These d a t a show t h a t w i t h i n each c o l o r / a r e a com-

b i n a t i o n t h e c r i t e r i o n , 50th p e r c e n t i l e , i n t e n s i t y v a l u e s a r e

q u i t e s i m i l a r a c r o s s a l l c o n d i t i o n s . The dusk/dawn and t h e n i g h t

d a t a show t h a t . t h e r e i s l i t t l e a f f e c t of t h e d i f f e r e n c e i n ambient

i l l u m i n a t i o n upon i n t o l e r a b l e d i scomfor t v a l u e s . The n i g h t and

dusk/dawn d i f f e r e n c e s t h a t were found a r e almost c e r t a i n l y due

t o t h e s u b j e c t groups and n o t t o t h e c o n d i t i o n s .

For t h i s reason t h e n i g h t , outdoor t e s t d a t a (shown i n

Appendix A - 2 ) were used t o determine t h e minimum daytime l e v e l s ,

by s e l e c t i n g t h e 25th p e r c e n t i l e n i g h t , i n t o l e r a b l e v a l u e s ,

ob ta ined a t t h e 75-foot viewing d i s t a n c e shown i n Table 2 ,11 ,

The r a t i o s of t h e 25th p e r c e n t i l e n i g h t (75 f e e t ) t o t h e 85th

p e r c e n t i l e mean (75 and 270 f e e t ) day candlepower v a l u e s , from

Table 2.9, a r e shown i n Table 2 . 1 2 , The mean r a t i o s i n Table

2 . 1 2 a r e t h e va lues by which daytime, 85th p e r c e n t i l e i n t e n s i t i e s ,

i n t h e r e s p e c t i v e c o l o r , should be m u l t i p l i e d t o o b t a i n t h e 25th

p e r c e n t i l e n i g h t , i n t o l e r a b l e i n t e n s i t y ,

DETERMINATION OF M I N I M U M AND MAXIMUM DAY AND N I G H T VALUES.

The maximum daytime i n t e n s i t y should be based upon t h e 85th per-

c e n t i l e day adequacy va lues shown i n Table 2.9, The minimum day

va lue i s ob ta ined by m u l t i p l y i n g t h e maximum va lue by t h e respec-

t i v e c o l o r r a t i o shown i n Table 2 . 1 2 . These v a l u e s apply a t H-V

of t h e lamp, and p r o p o r t i o n a l minimum va lues t o those recommended

i n SAE J575c (1966) should be found a t t h e i n d i c a t e d test p o i n t s .

Given a lamp of known luminous a r e a it i s p o s s i b l e t o d e t e r -

mine t h e luminance wi th r e s p e c t t o a lamp of 12.6 square inches

by use of Figure 2 . 4 . This procedure g i v e s a luminance r a t i o cor-

r e c t i o n f o r a r e a L A '

I f t h e c o l o r of t h e lamp i s n o t r e d then a c o r r e c t i o n f o r

c o l o r must be made us ing t h e mean c o l o r / r e d luminance r a t i o s f o r

day and n i g h t i n Table 2.6, This procedure g ives luminance r a t i o

c o r r e c t i o n s f o r c o l o r :

DAY

L~ NIGBT The day maximum va lue i s found by o b t a i n i n g t h e 85th p e r c e n t i l e

luminance of t h e 12.6-square-inch, r e d lamp from Table 2 . 9 and

m u l t i p l y i n g by t h e c o r r e c t i o n f a c t o r s , LA x LC DAY.

TABLE 2.11. 25th PERCENTILE I N T E N S I T Y VALUES JUDGED INTOLERABLE BY 32 COLOR-NORMAL SUBJECTS FOR EACH COLOR, AND LAMP AREA, AT 75 FEET

TABLE 2.12. RATIO OF 25th PERCENTILE NIGHT/ 85th PERCENTILE DAY CANDLEPOWER VALUES FOR EACH AREA AND COLOR

A r e a (sq. G r e e n - i nches ) W R A B l u e

6.1 .06 -14 . .06

G r e e n - B l u e

110

233

207

236

242

A r e a (sq. i n c h e s )

6.1

12.6

25.2

37.8

12. 6H

MEAN RATIO .05 .13 .07 .09 ['MIN/MaX]

O r n r n i t t i n g 4.0 sq. inch lamp

A

431

565

445

86 3

427

W

675

695

845

982

683

R

248

257

431

627

293

The 85th p e r c e n t i l e luminance of t h e 12.6-square-inch, r ed

lamp is:

2536/12.6 = 187 candles/sq. inch

Therefore, day maximum i n t e n s i t y / u n i t a r e a (c/sq. i n c h ) :

D M A ~ = 187 x LA x LC DAY

The day minimum va lue i s ob ta ined by t h e use of t h e r a t i o ,

f o r t h e r e s p e c t i v e c o l o r , shown i n Table 2.12, This procedure

g ives a minimum/maximum r a t i o c o r r e c t i o n f o r each co lo r :

Therefore , day minimum candlepower i s :

The n i g h t maximum va lue i s found by f i r s t o b t a i n i n g t h e 15th

p e r c e n t i l e , r e d , 12.6 square inch luminance from Table 2.3. This

va lue i s 15.3 candles /square inch.

I t then fo l lows t h a t t h e night-maximum value (c/sq. i n c h ) :

The n i g h t minimum can be de r ived i n t h e same way us ing t h e

luminance of t h e e s t a b l i s h e d r e d , Class-A lamp minimum of 80 Cp,

i . e . , 80/12,0 = 6 . 6 candles/square i n c h , a s a cons tan t . Thus,

n i g h t minimum is:

For example, f o r a lamp of 20 square i n c h e s , i n r e d , t h e day-

t i m e maximum va lue is:

DMAx = 187 x L x LC DAY A

= 187 x 0.765 x 1, c/sq. inch

= 143 c/sq. inch

o r , 143 x 20 = 2860 cp.

8 0

For t h i s lamp t h e minimum day v a l u e shou ld be :

Day i n t e n s i t y v a l u e s shou ld be 2860 - 372 cp f o r a r e d lamp of

20 s q u a r e i n c h e s . The n i g h t maximum v a l u e f o r t h e same lamp:

- N M A ~ - 15*3 L~ N I G H T (c / sq . i n c h )

NMAx = 15 .3 x 0.765 x 1 c /sq . i n c h

= 11.70 c / sq . i n c h

o r = 11.70 x 20 = 234 c p

N~~~ = 0.43 Nmx = 5.03 c / sq . i n c h

o r = 5.03 x 20 = 1 0 1 c p

T h e r e f o r e , n i g h t i n t e n s i t y v a l u e s shou ld be 234-101 c p f o r a r e d

lamp of 20 s q u a r e i n c h e s .

I n t h e ana logous manner maximum and minimum, day and n i g h t

i n t e n s i t i e s f o r lamps having o t h e r a r e a s and c o l o r s , w i t h i n t h e

range o f t h o s e used i n t h e s e t e s t s , can be de te rmined ,

The s t e p s t h a t a r e used i n t h e computat ion a r e summarized

a s f o l l o w s :

(1) DAY-MAXIMUM ( c / sq , i n c h )

( 2 ) DAY-MINIMUM

( 3 ) NIGHT-MAXIMUM ( c / sq . i n c h )

( 4 ) N I G H T - M I N I M U M

N~~~ = 0.43 Nmx

The d a t a needed t o make t h e computa t ions a r e summarized f o r

convenience i n u s e i n F i g u r e 2 .5 , which shows t h e p l o t of LA (from

COLOR

-.

CDAY

LUMINOUS AREA (SQ, INCHES)

FIGURE 2.5. Summary of Constants

Figure 2 . 4 ) and t h e d a t a f o r L (from Table 2.6) and 'DAY L c N I G H ~

'MIN/MAX from Table 2.12) . Figures 2.6-2.8 show t h e day and n i g h t i n t e n s i t y minima and

maxima f o r r e d , amber and green-blue, a s a f u n c t i o n of t h e lamp

a r e a , which were d e r i v e d u s i n g t h e above procedure,

0 0 0 8 0 0 0 0 0 0 0 0 0 0 0 0

0 0 0

8 0 0 0

0 0 0

' 0 0 0

0 0 0 9 0 0 800 700 6 0 0

5 0 0

400

3 0 0

200

1 0 0 9 0 8 0 7 0

6 0

5 0

4 0

3 0

. 5


F i g u r e 2 . 6 . Red, Day and Night Minimum and Maximum I n t e n s i t y a s a Func t ion of Lamp Area

8 4

Figure 2.7. Amber, Day and Night Minimum and Maximum Intensity as a Function of Lamp Area

8 5

10,000 9,000 1 I I -

8,000 --- 7,000.

z 3 V

* H H a - W B W

1 0 0 9 0 8 0 7 0 6 0

5 0

4 0

3 0

o*/ 5 1 0 1 5 2 0 2 5 3 0 35 37.5


4,000 :

3 ,000

2,000

h 1,000 900 . 800

0 PI 700 W 4 600 n

DAY

F i g u r e 2 .8 . Green-Blue , Day a n d N i g h t Minimum and Maximum I n t e n s i t y as a F u n c t i o n o f Lamp A r e a

8 6

10 ,000 9 , 0 0 0 ~ 8 , 0 0 0 - 7 , 0 0 0 ~ 5 ,000

5 , 0 0 0

4 ,000

3 , 0 0 0 . A

-

2 , 0 0 0

200

I w

1 0 0 . 9 0 8 0 . 7 0

6 0

5 0

4 0

Nmin 3 0 i "

0 5 1 0 1 5 20 2 5 3 0 35 37.5

LUMINOUS AREA ( SQ. INCHES)

A v

v

- 1 , 0 0 0 ~ G 900 g 800

700

600 CI

5 0 0 , U - 400 w B H m 3 0 0 . El B 4

DAY

z

3 . DRIVER SWITCHING AND FEEDBACK MODE REQUIREMENTS FOR MULTI- INTENSITY LIGHTING (TASK 3 )

The r e s u l t s of Task 2 have shown t h a t more t h a n one i n t e n -

s i t y i s r e q u i r e d t o s a f i s f y day and n i g h t v i s i b i l i t y r e q u i r e -

ments f o r s i g n a l lamps. For a t w o - i n t e n s i t y system, t h e i n t e n -

s i t i e s could be media ted by o p e r a t i o n of t h e h e a d l i g h t s w i t c h .

Whenever t h e h e a d l i g h t s were t u r n e d o f f t h e system would be

a u t o m a t i c a l l y p l a c e d i n t h e h i g h e r s i g n a l i n t e n s i t y mode t o be

used i n dayt ime o p e r a t i o n . I n n i g h t t i m e o p e r a t i o n when t h e

h e a d l i g h t s a r e t u r n e d o n , t h e r e a r s i g ~ a l l i g h t i n t e n s i t y

would a u t o m a t i c a l l y be p l aced a t t h e lower l e v e l . I n t h i s way

normal d r i v e r a c t u a t i o n of t h e h e a d l i g h t s w i t c h would s e l e c t

t h e a p p r o p r i a t e r e a r l i g h t i n g s i g n a l i n t e n s i t y . Simple mod-

u l a t i o n of r e a r s i g n a l i n t e n s i t y t h rough t h e h e a d l i g h t s w i t c h

would n o t r e q u i r e any complex swi t ch ing systems t o be a c t u a t e d

by t h e d r i v e r o r , p e r h a p s , by some a u t o m a t i c system which cou ld

s e n s e t h e ambient l i g h t l e v e l and a tmospher ic t r a n s m i s s i o n .

There a r e a number of shor tcomings t o t h i s approach. For

example, i n poor v i s i b i l i t y dayt ime d r i v i n g c o n d i t i o n s , such a s

snow, fog o r h a z e , i n which it would be a p p r o p r i a t e t o o p e r a t e

s i g n a l l i g h t s a t t h e h i g h i n t e n s i t y l e v e l , t h e lamps would

a c t u a l l y o p e r a t e a t t h e low i n t e n s i t y , n i g h t l e v e l because

d r i v e r s t e n d t o t u r n on t h e i r h e a d l i g h t s i n t h e s e c o n d i t i o n s .

The same s i t u a t i o n would a r i s e urider poor v i s i b i l i t y c o n d i t i o n s

a t n i g h t i n which it would be d e s i r a b l e t o u t i l i z e t h e h i g h e r

i n t e n s i t y .

While it i s t r u e t h a t c o n t r o l l i n g i n t e n s i t y by t h e head-

l i g h t swktch may n o t r e n d e r t h e d u a l i n t e n s i t y system any poorer

t h a n under s i m i l a r c o n d i t i o n s now, it would n o t u t i l i z e t h e po t -

e n t i a l of such a system.

I n o r d e r t o p r o v i d e f o r g r e a t e r v e r s a t i l i t y i n t h e a v a i l -

a b i l i t y o f i n t e n s i t y l e v e l s f o r t h e r e a r s i g n a l s i n day o r n i g h t

fog and o t h e r poor atmospheric c o n d i t i o n s , an o v e r r i d e swi tch

f o r opera t ion by t h e d r i v e r would have t o be provided. This

swi tch would al low t h e high i n t e n s i t y l e v e l t o be s e l e c t e d ir-

r e s p e c t i v e of t h e headlamp swi tch p o s i t i o n . For example, i f

t h e headlamps were turned on i n daytime t h e d r i v e r could o p e r a t e

t h e i n t e n s i t y o v e r r i d e swi tch t o p l a c e h i s r e a r s i g n a l s on t h e

daytime i n t e n s i t y . The same s i t u a t i o n would hold under n i g h t

d r i v i n g cond i t ions i n which t h e h e a d l i g h t s would normally be

i n use , The d isadvantage of such a n arrangement i s t h a t it

may be misused by d r i v e r s . This could occur i f t h e h igh s i g n a l

i n t e n s i t y i s used under normal atmospheric , n i g h t d r i v i n g con-

d i t i o n s , r e s u l t i n g i n d iscomfor t and d i s a b i l i t y g l a r e t o follow-

ing d r i v e r s .

The e x t e n t t o which t h e s i g n a l i n t e n s i t y o v e r r i d e swi tch

would be misused i n a c t u a l p r a c t i c e i s d i f f i c u l t t o a s c e r t a i n .

I t seems f a i r l y s a f e t o assume t h a t , i f a d r i v e r i s b l inded

by t h e s i g n a l l i g h t s of a c a r ahead of him i n c o n d i t i o n s i n

which it would be i n a p p r o p r i a t e f o r t h e l ead c a r t o be us ing

high i n t e n s i t y ( e i t h e r on purpose o r i n a d v e r t e n t l y ) , t h e f o l -

lowing d r i v e r would r e a c t i n much t h e same way t h a t d r i v e r s

do now t o an oncoming v e h i c l e us ing i t s h igh beam. I n such

s i t u a t i o n s d r i v e r s r e a c t f a i r l y r a p i d l y by f l a s h i n g t h e i r high

beam a t t h e approaching d r i v e r who t h e n , i n almost a l l c a s e s ,

responds by dimming h i s l i g h t s t o t h e low beam. A s i m i l a r

s i t u a t i o n would hold f o r t h e high s i g n a l i n t e n s i t y which may

be annoying t o a fol lowing d r i v e r . He could a l e r t t h e l ead

c a r d r i v e r by f l a s h i n g h i s high beam h e a d l i g h t s , which would

s i g n a l him t o r e v e r t t o t h e normal, n i g h t i n t e n s i t y s i g n a l s . I t i s assumed t h a t t h i s type of behavior would occur and

r e s u l t i n a p p r o p r i a t e use of t h e s i g n a l i n t e n s i t y o v e r r i d e

swi tch .

However, it i s important f o r a d r i v e r t o be aware of t h e

s t a t u s of an i n t e n s i t y o v e r r i d e swi tch i n both n i g h t and daytime

c o n d i t i o n s . For t h i s r eason some g e n e r a l human eng inee r ing

c o n s i d e r a t i o n s a r e necessa ry i n t h e l a b e l i n g of such a swi tch

c o n t r o l and i n t h e means by which feedback i s provided t o t h e

d r i v e r of t h e s t a t u s of t h e swi tch .

The i n t e n s i t y o v e r r i d e swi tch should be l a b e l e d c l e a r l y

t o d e s i g n a t e i t s o p e r a t i o n . For example, t h e swi tch may be

l a b e l e d " s t o p / t u r n i n t e n s i t y " , and t h e two p o s i t i o n s could be

l a b e l e d "high" and "normal", corresponding t o t h e l o c a t i o n of

t h e swi tch s e t t i n g . The swi tch p o s i t i o n should be c l e a r l y

known t o t h e d r i v e r , and t h e r e f o r e push-pul l swi tches should

n o t be used . Toggle, r o t a r y and rocker swi tches a r e s u i t a b l e .

Some p o s s i b l e arrangements f o r swi tches and legends a r e sugges-

t e d i n ~ i g u r e 3 . 1 a s g e n e r a l performance g u i d e l i n e s .

I n a d d i t i o n t o legend and swi tch p o s i t i o n a s i n d i c a t o r s of

swi tch s t a t u s , a c l e a r feedback s i g n a l of h igh i n t e n s i t y s i g n a l

o p e r a t i o n may be provided. Such a s i g n a l should be e i t h e r a

sound o f a p p r o p r i a t e i n t e n s i t y and frequency spectrum t o be

c l e a r l y a u d i b l e o r a l i g h t s u i t a b l y p laced on t h e dash pane l .

I f a l i g h t i s used it must be c l e a r l y v i s i b l e t o t h e d r i v e r

i n bo th day and n i g h t d r i v i n g c o n d i t i o n s i n which t h e o v e r r i d e

swi tch may be i n u s e . S ince t h e s e c o n d i t i o n s a r e t h o s e i n

which t h e ambient l e v e l i s probably lower t h a n i n normal

daytime l e v e l s , a l though daytime f o g s can have a f a i r l y high

background luminance, it i s p o s s i b l e t h a t a s i n g l e i n t e n s i t y

l e v e l i s adequate f o r t h e feedback l i g h t . The feedback l i g h t

should be color-coded amber t o i n d i c a t e t h a t it i s a second

o r d e r , warning s i g n a l .

I t would probably be u n d e s i r a b l e t o have e i t h e r t h e

a u d i t o r y o r v i s u a l feedback s i g n a l on con t inuous ly . Therefore ,

t h e s i g n a l should on ly be g iven f o r a maximum of 1 - 2 seconds

wi th t h e s t o p s i g n a l . This would p rov ide feedback of t h e

o p e r a t i o n of s t o p s i g n a l s (and " r i d i n g " t h e brake p e d a l ) a s we l l

a s reminding d r i v e r s they were on t h e h igh i n t e n s i t y s e t t i n g .

I t would a l s o o b v i a t e t h e annoyance t h a t may be caused by having

e i t h e r an a u d i t o r y o r v i s u a l s i g n a l on a t a l l t imes o r f o r long

8 9

Figure 3 .1 . Suggested legend and type of swi tch ope ra t i on f o r manual i n t e n s i t y ove r r i de .

9 0

t ime p e r i o d s . The s i g n a l must a t t r a c t a t t e n t i o n wi thout being

annoying s o t h a t d r i v e r s do n o t i n t e r f e r e w i t h t h e wi r ing o r

mask t h e s i g n a l .

Three s t e p s should be t a k e n i n o r d e r t o s p e c i f y recornenda t ions

f o r a s t o p and t u r n s i g n a l i n t e n s i t y o v e r r i d e swi tch f o r manual

o p e r a t i o n by d r i v e r s : (1) t h e swi tch should be c l e a r l y l a b e l e d ,

( 2 ) t h e s e t t i n g of t h e swi tch should be c l e a r l y i d e n t i f i a b l e

t o t h e d r i v e r by o b s e r v a t i o n of t h e swi tch p o s i t i o n , ( 3 ) an

a u d i t o r y o r v i s u a l feedback s i g n a l should be of s u f f i c i e n t

i n t e n s i t y t o be c l e a r l y n o t i c e a b l e i n day and n i g h t d r i v i n g and

t o be a c t u a t e d f o r 1 - 2 seconds whenever t h e s t o p s i g n a l i s g iven .

One way to increase the efficacy of rear signal systems is

to increase the probability that such signals are seen. Conven-

tional mounting standards do not ensure that a rear lamp system

will be visible in all of the commonly encountered traffic situa-

tions in which it is defensively advantageous for the driver of

one vehicle to see a rear signal of another vehicle. An analysis

of such traffic situations (which are described below) led to the

recognition that side-mounted turn signals would very efficiently

supplement conventionally located rear signals.

The questions under investigation in the studies reported

below involve recommendations for mounting position, size and

intensity for side-mounted turn signals. This task was approached

by dividing the problem into two areas and attacking each inde-

pendently. First, a recommended mounting position for a side-

mounted signal was established; then, the size, intensity, and

intensity distribution characteristics required for such a system

were investigated.

LONGITUDINAL LOCATION ANALYSIS. The question of optimal

longitudinal placement of side turn signals can be solved analy-

tically. Such systems should be placed to provide visibility

of the signal in at least two classes of situations.

Figure 4.1 represents the case in which two vehicles travel-

ing in the same direction are nearly abreast of each other in

the first and third lanes of a divided highway. Either or both

drivers may want to move into the empty middle lane, but con-

ventional signaling systems preclude the safe communication of

such an intention. Rather, the driver intending such a move

must closely monitor the other vehicle, two lanes removed, to

the detriment of his awareness of the traffic in his own lane.

In such situations both drivers frequently make a simultaneous

start to change lanes, perhaps leading to a collision. There

is a potential safety benefit in a side-mounted signal in such

F i g u r e 4 . 1 . T r a f f i c s i t u a t i o n d e p i c t i n g v e h i c l e s a b r e a s t of each o t h e r i n t h e f i r s t and t h i r d l a n e s of a t r i p l e l a n e highway.

circumstances, and no analysis is required to conclude that it

should be mounted as far forward as possible.

Figure 4.2 represents a road having two lanes of traffic

moving in the same direction. This situation is especially per-

tinent when cars in the left lane are fairly well spaced and

moving fast relative to a more closely bunched line of traffic

on the right. In such circumstances it is often impossible for

a driver in the left lane to see the rear left turn signal of a

vehicle some distance ahead which may be attempting to enter the

faster lane of traffic. Figure 4.2 and the actual road scene

(Figure 4.3) depict the superiority of forward mounting for a

side turn signal.

VERTICAL LOCATION STUDY. With a strong argument thus estab-

lished for a forward mounting position, the question of the

desirable vertical mounting height of a side-marker signal was

addressed. There is no vertical visibility problem looking out

of the driver's side of a vehicle. It was also established that

the tallest drivers may have little upward visibility through

the front passenger door window. This suggests that upper mount-

ing height for a side turn signal should not be above the seated

height of the tall driver. The minimum vertical mounting

height of a side turn signal required empirical analysis.

A laboratory study was run with the purpose of setting lower

bounds of the vertical mounting height of side turn signals,

Measurements were made of the visibility of drivers representing

the lower range in the dimension of sitting height from a repre-

sentative range of vehicles.

Method. Subjects. Twenty-two female subjects participated in

this study, ranging in standing height from 4 feet, 10 inches, to

5 feet, 3 inches, and averaging 5 feet, 1 1/2 inches. More per-

tinent, their sitting heights varied from 31.5 inches to 34.0

inches and averaged 32.6 inches, or approximately the 25th per-

centile of the female population (Damon et al., 1966).

Parget Vehicle 4

--- ,-,--- - --- --------- Line of Vision to T

4 Passing Vehicle

Figure 4 . 2 . T r a f f i c s i t u a t i o n dep ic t ing t h e ca se i n which a r e a r mounted t u r n s i g n a l on v e h i c l e "T" would be obscured t o a d r i v e r of a v e h i c l e i n t h e pass ing l a n e , and showing t h e increased f i e l d of view provided by t h e s i d e mounted t u r n s i g n a l .

F i g u r e 4 . 3 . D r i v e r ' s v i e w in t h e passing lane.

Procedure. Three r e p r e s e n t a t i v e v e h i c l e s were employed i n

t h i s s tudy : A 1969 Camaro, Chevel le , and Impala. For each sub-

j e c t i n each v e h i c l e a p r o f i l e was developed of t h e s u b j e c t ' s

view forward and t o t h e r i g h t s i d e of t h e v e h i c l e . S u b j e c t s were

s e a t e d i n t h e d r i v e r ' s p o s i t i o n a s they would be i f they were

d r i v i n g t h e c a r , and i n s t r u c t e d t o f a s t e n t h e s e a t b e l t and gen-

e r a l l y o r i e n t t h e i r body p o s i t i o n a s they would f o r normal d r i v -

ing . The t e s t v e h i c l e s were p o s i t i o n e d p a r a l l e l t o a w a l l a t a

d i s t a n c e of 4 f e e t from t h e w a l l , measured from t h e r i g h t s i d e of

t h e v e h i c l e . Mounted v e r t i c a l l y a long t h e w a l l were 2 6 yard-

s t i c k s , spaced one f o o t a p a r t , cover ing a d i s t a n c e extending f o r -

ward from approximately a b r e a s t of t h e d r i v e r ' s eye p o s i t i o n .

A t each of t h e y a r d s t i c k p o s i t i o n s t h e experimenter s lowly

r a i s e d a smal l l i g h t u n t i l t h e s u b j e c t s i g n a l l e d t h a t she was

j u s t a b l e t o s e e it. S u b j e c t s were cau t ioned n o t t o s t r a i n o r

o the rwise compromise t h e i r normal d r i v i n g p o s i t i o n i n o r d e r t o

s e e t h e l i g h t a t a lower p o i n t .

R e s u l t s . A p r o f i l e was p l o t t e d f o r each s u b j e c t i n each c a r

of t h e minimum v e r t i c a l h e i g h t a t which t h e l i g h t was seen a t

each y a r d s t i c k l o c a t i o n .

The d a t a were pooled a c r o s s s u b j e c t s i n each v e h i c l e and

p r o f i l e s were developed r e p r e s e n t i n g t h e median and 25th percen-

t i l e d a t a . These g raphs , which can be seen i n F igures 4 . 4 through

4.6, were a d j u s t e d t o e x c i s e any p o i n t s a t which t h e "A" p i l l a r

i t s e l f o b s t r u c t e d v i s i o n of a p a r t i c u l a r y a r d s t i c k . A t such p o i n t s

a va lue was i n s e r t e d midwa.y between t h e y a r d s t i c k read ings t o

e i t h e r s i d e of t h e o b s t r u c t e d s t i c k , I n c l u s i o n of d a t a a f f e c t e d

by "A" p i l l a r blockage would have l e d t o an argument f o r a r t i f i -

c i a l l y h igh minimum mounting h e i g h t s , f o r such p o i n t s were o f t e n

more than 1 2 i n c h e s above any o t h e r p o i n t on a s u b j e c t ' s p r o f i l e .

However, t h e h o r i z o n t a l d i s t a n c e over which such blockage occurred

was never more than a few inches a t t h e 4-foot v e h i c l e s e p a r a t i o n .

From t h e f i g u r e s it can be seen t h a t a l l t h e median and 25th

~ e r c e n t i l e p r o f i l e s a r e below t h e 34-inch mark f o r a l l v e h i c l e s

t e s t e d . An i n v e s t i g a t i o n showed t h a t f o r most American passenger

9 7

20 19 18 17 16 15 14 13 1 2 11 10 9 B 7 6 5 4 3

Distance in Feet Measured Forward From Subject's Eye Position

Figure 4.4. 50th and 25th percentile rightside visibility profiles for subjects in 1969 Chevrolet Camaro.

Distance in Feet Measured Forward From Subject's Eye Position

Figure 4.5, 50th and 25th percentile rightside visibility profiles for subjects in 1969 Chevrolet Chevelle.

D i s t a n c e i n F e e t Measured Forward From S u b j e c t ' s Eye P o s i t i o n

F igure 4 . 6 . 50th and 25th p e r c e n t i l e r i g h t s i d e v i s i b i l i t y p r o f i l e s f o r s u b j e c t s i n 1969 Chevrole t Impala.

cars fender tops were in the 33-inch to 38-inch height range.

Since the mean sitting height of the female subjects was

about 32.6 inches, which is the 25th percentile of the female

population's sitting height, the 50th percentile visibility pro-

file should represent the 50th percentile visibility of the 25th

percentile female population. Similarly the 25th percentile

visibility profile approximates the 50th percentile values that

would be found for 12th percentile females in sitting height.

Taking this percentile profile as a cut-off for recommended min-

imum mounting height should approximately accomodate the 12th

percentile female and the 1 percentile male (Stoudt et al., 1965).

The findings from both the analytical and experimental

mounting position studies point to a far-front (fender) mounting,

at a minimum height of about 33 inches and a maximum of 48 inches.

The latter value was based on a driver's seated eye height which

will limit upward visibility particularly to the right of the

driver (Meldrum, 1965). SAE recommended practice, 5-914 (1965),

"Side Turn Signal Lamps," indicates a mounting height between 36

inches an6 72 inches. The recommendations derived from the pre-

sent study would allow a lower minimum and maximum mounting height,

SIGNAL AREA AND INTENSITY. Very straightforward methods

have been available for establishing placement recommendations

for side-mounted turn signals, but a much more complicated and

ambiguous question concerns the size and intensity of such lamps.

Viewing problems are encountered which are unlike those of any

conventional signal system. First of all, side-mounted signals

will seldom be viewed directly in traffic at 90 degrees (Figure

4.7) by drivers of vehicles traveling in the same direction,

and at this angle by others only at intersections, However,

when such a signal is viewed at 90 degrees from a vehicle travel-

ing in the same direction, it will likely be by a driver who is

abreast of the target vehicle and only one or two traffic lanes

removed. Such viewing may often be peripheral and require a high

intensity unless the driver turns his head and eyes for a direct

F i g u r e 4 . 7 . Diagram d e f i n i n g r a d i a t i o n a n g l e s r e f e r r e d t o i n t h i s s t u d y .

view. I t w i l l have t o be reso lved whether t o supply s u f f i c i e n t

l i g h t f o r t h e d r i v e r looking i n t h e d i r e c t i o n of t h e l i g h t source

a t a 10-20 f o o t d i s t a n c e o r f o r one whose v i s u a l o r i e n t a t i o n i s

90 degrees removed from t h a t source and a long t h e d i r e c t i o n of

t r a v e l .

S ide t u r n s i g n a l s w i l l a l s o need t o be adequa te ly v i s i b l e a t

a n g l e s a s smal l a s 5 degrees wi th t h e long a x i s of t h e v e h i c l e a t

d i s t a n c e s of 150 f e e t o r g r e a t e r . Assuming t h a t a given s i d e t u r n

s i g n a l was a f l a t , round lamp mounted a long t h e 0 degrees a x i s i n

F igure 4.7, t h e n , t h e f u r t h e r away t h e l i g h t i s viewed t h e s m a l l e r

w i l l be t h e p r o j e c t e d luminous a r e a i n t h a t d i r e c t i o n . This means

t h a t t h e lamp would probably be mounted a t an ang le l a r g e r than 0

d e g r e e s , f a c i n g rearward.

Method.

Apparatus. I n t h e p r e s e n t s tudy t h e l i g h t source used

was a s e a l e d beam lamp, 4 . 0 i nches i n d iamete r , wi th a sp read ing

l e n s des igned t o provide + 2-1/2 degrees v e r t i c a l and + 5 degrees

h o r i z o n t a l uniform candlepower o u t p u t . An amber f i l t e r was

p laced i n f r o n t of t h e lamp, behind one of t h r e e cardboard over-

l a y s having openings of 1 / 2 i n c h , 1 -1 /2 inches and 3.0 inches

i n d iamete r . The r e s u l t i n g lamp a r e a s a r e : 0.79, 1.75 and 7 . 1

square inches . The lamp was mounted on a t r i p o d behind a s t a n d ,

p a i n t e d f l a t whi te , wi th a 4-inch d iameter h o l e s o t h a t t h e

lamp was f l u s h wi th t h e back of t h e 1 / 4 i nch t h i c k board (F igure

4 . 8 ) . An A/C power source ,providing v a r i a b l e D/C between 0 and

13 v o l t s was used t o e n e r g i z e t h e lamp. ~ i g h t o u t p u t was measured

wi th a P r i t c h a r d photometer t o candlepower e q u i v a l e n t s f o r every

1 / 2 v o l t from 0 t o 13 v o l t s a t H-V.

Procedure. I n i t i a l l y , t h e p lan was t o run t h e s tudy o u t of

doors , under ambient l i g h t i n g i n d a y l i g h t , t w i l i g h t , and n i g h t

c o n d i t i o n s . However, c i rcumstances prevented t h e accumulation of

n i g h t and t w i l i g h t d a t a a t a s u f f i c i e n t r a t e , and t h u s a p a r t of

t h a t s t u d y was moved i n t o t h e l a b o r a t o r y and run under s l i g h t l y

d i f f e r e n t c o n d i t i o n s from t h e o u t s i d e , d a y l i g h t , s tudy .

103

F i g u r e 4 . 8 . S i d e t u r n s i g n a l i n t e n s i t y t e s t a r r a n g e - ment , showing t e s t lamp sur round and s u b j e c t i n t h e v e h i c l e .

Day and Night F i e l d Experiment. T h i r t y s u b j e c t s , p r i -

m a r i l y U n i v e r s i t y of Michigan s t u d e n t s , p a r t i c i p a t e d i n t h e f i e l d

daytime experiment . S u b j e c t s were s e a t e d i n a v e h i c l e (F igure

4 . 8 ) f a c i n g t h e tripod-mounted lamp a t each of two d i f f e r e n t d i s -

t a n c e s , 30 f e e t and 100 f e e t (measured from t h e s u b j e c t t o t h e

lamp). Each s u b j e c t was run a t each d i s t a n c e wi th a l l t h r e e lamp

a r e a s and a t each of t h r e e v i s u a l a n g l e s t o t h e l i g h t source .

I n t h e 0 degree c o n d i t i o n t h e s u b j e c t was asked t o blow t h e

c a r horn when t h e g r a d u a l l y i n c r e a s i n g l i g h t f i r s t became v i s i b l e

and aga in when and i f t h e l i g h t reached a b r i g h t n e s s l e v e l which

he thought was o b j e c t i o n a b l y b r i g h t .

I n t h e 5 degree ( a t 1 0 0 f e e t o n l y ) and 30 degrees ( a t 30

f e e t o n l y ) c o n d i t i o n s , i n s t r u c t i o n s were i d e n t i c a l t o those above

f o r t h e 0 degree c o n d i t i o n excep t t h a t t h e s u b j e c t was asked t o

look i n t h e d i r e c t i o n of a t a r g e t which was p laced a t t h e respec-

t i v e ang le t o t h e t e s t lamp, e q u i d i s t a n t wi th t h e lamp from t h e

s u b j e c t . I n s t e a d of blowing t h e horn a second t ime f o r " t o o

b r i g h t " , t h e s u b j e c t was i n s t r u c t e d t o respond a second time when

and i f t h e l i g h t reached a l e v e l which he a s s e s s e d a s b r i g h t enough

t o be "adequa te ly attention-commanding a s a s i g n a l l i g h t . " Sub-

j e c t s were i n s t r u c t e d t o look i n t h e d i r e c t i o n of t h e t a r g e t .

Then, obse rv ing t h e t e s t lamp i n t h e pe r iphery of t h e i r v i s u a l

f i e l d , they were t o respond a s d e s c r i b e d when t h e l i g h t was j u s t

v i s i b l e and then adequa te ly b r i g h t ,

Under each d i s t a n c e , a n g l e , and lamp a r e a c o n f i g u r a t i o n ,

each s u b j e c t responded twice a s t h e l i g h t i n t e n s i t y was be ing

i n c r e a s e d . The r a t e of i n c r e a s e was v a r i e d over t r i a l s . A

s u b j e c t performed a t each angu la r c o n f i g u r a t i o n a t one d i s t a n c e

b e f o r e be ing t e s t e d a t t h e o t h e r d i s t a n c e .

p e r i o d i c a l l y photometr ic measurements were taken i n t h e day-

t ime t o a s s e s s t h e luminance of t h e whi te board , r e f l e c t a n c e 9 8

p e r c e n t , which c o n s t i t u t e d t h e viewing background of t h e t e s t lamp.

Nine i n d i v i d u a l s p a r t i c i p a t e d i n t h e n i g h t phase and seven i n

t h e t w i l i g h t c o n d i t i o n . This s tudy was run i n an i d e n t i c a l f a sh ion

t o t h e daytime experiment. The luminance of t h e tes t lamp sur-

round board v a r i e d from 1 t o 850 foot - lamber ts i n t h e dusk tests

a s compared t o a c o n s t a n t 40 foot - lamber ts i n t h e l abora to ry .

Dusk and Night Laboratory Experiment. S ix ty-four sub-

j e c t s were run i n t h e l a b o r a t o r y phase of t h e s tudy (Figure 4 .9 ) .

These s u b j e c t s were d iv ided i n t o f o u r s e c t i o n s , according t o t h e

l i g h t i n g ( t w i l i g h t - n i g h t ) and d i s t a n c e (30 f e e t and 100 f e e t ) .

S u b j e c t s were run i n p a i r s , i n s t e a d of s i n g l y a s i n t h e daytime

s tudy. They were s e a t e d s i d e by s i d e and given a s i l e n t , push-

b u t t o n swi tch which they were i n s t r u c t e d t o hold i n such a manner

t h a t each could n o t s e e t h e o t h e r ' s swi tch o r be a b l e t o a s c e r t a i n

when a response had been made. Responses were recorded on a s t r i p -

c h a r t r e c o r d e r , Each s u b j e c t responded t h r e e t imes: once f o r t h e

v i s u a l t h r e s h o l d , again f o r adequate ly b r i g h t , and f i n a l l y f o r

" t o o b r i g h t . " I n a l l o t h e r r e s p e c t s t h i s phase of t h e s tudy

was i d e n t i c a l i n procedure t o t h e day and n i g h t f i e l d s t u d i e s .

Resu l t s . The 25th , 50th and 75th p e r c e n t i l e c r i t e r i o n

response i n t e n s i t y va lues were computed f o r each t e s t t r ea tment .

These va lues a r e given i n Tables 4 . 1 through 4.5. Table 4.6

shows 90th p e r c e n t i l e d a t a f o r day and dusk f o r a b s o l u t e v i s i -

b i l i t y t h r e s h o l d s only.

One obvious i m p l i c a t i o n of Tables 4 . 1 through 4.6 i s t h a t ,

f o r any c o n d i t i o n , r e q u i r e d candlepower i s an i n c r e a s i n g func t ion

of lamp a r e a . I t fo l lows t h a t i n t e n s i t y s t a n d a r d s , i f given i n

candlepower, should be q u a l i f i e d according t o lamp a r e a . These

recommendations a r e thus q u a l i f i e d .

It i s e v i d e n t from t h e t a b l e s t h a t even f o r a d u a l i n t e n s i t y

system, compromises must be made between daytime and/or dusk

b r i g h t n e s s adequacy, and a l s o dusk and n i g h t o b j e c t i o n a b i l i t y

l e v e l s , This i s p a r t i c u l a r l y t r u e a t one of t h e p e r i p h e r a l view-

ang les . For example, a t 30 f e e t , a 3.0 inch d iameter ( 7 . 1

square i n c h e s ) l i g h t i n t e n s e enough t o be cons idered adequate ly

Figure 4 . 9 . The laboratory t e s t arrangement.

TABLE 4.1. DAY M I N I M U M , ADEQUATE, AND MAXIMUM CANDLE- POWER PERCENTILES FOR THREE LAMP AREAS, TWO VIEWING DISTANCES, AND THREE FIXATION ANGLES. FIELD STUDY DATA FOR 30 SUBJECTS

Cond i t ion Dis t /AngleO/Crite ria

3 0 ' / O 0 / min

3 0 ' / O 0 / max

3 0 ' / 15' / min

3 0 ' / 15' / adeq

l o o ' / 0 ° / min

l o o ' / O 0 / max

l o o ' / 5' / min

1001 / 5" / adeq

7 . 1 s q . i n c h e s 1 - 7 5 s q . i n c h e s 0.19 s q . i n c h e s P e r c e n t i l e I p e r c e n t i l e I p e r c e n t i l e

Note: Whenever a v a l u e a p p e a r s preceded by > a s i n >x, t h i s means no r e sponse had been e l i c i t e d a t t h e maximum i n t e n s i t y of t h e lamp and x i s t h e maximum v a l u e .

TABLE 4 .2 . DUSK M I N I M U M , ADEQUATE, AND MAXIMUM CANDLE- POWER PERCENTILES FOR THREE LAMP DIAMETERS, TWO VIEWING DISTANCES, AND THREE FIXATION ANGLES. LABORATORY STUDY DATA FOR 30 SUBJECTS

Note: Wheneve r a v a l u e a p p e a r s p r e c e d e d by > as i n >x , t h i s m e a n s n o r e s p o n s e h a d b e e n e l i c i t e d a t t h e maximum i n t e n s i t y of t h e l a m p a n d x i s t h e maximum value .

C o n d i t i o n

Dist/AngleO/Criterion

3 0 1 / O 0 / min

3 0 1 / O 0 / a d e q

3 0 1 / O 0 / max

3 0 1 / 1 5 ' / min

3 0 1 / 1 5 ' / a d e q

3 0 1 / 15O / max

1 0 0 1 / O 0 / m i n

1 0 0 1 / O 0 / adeq

1 0 0 1 / O 0 / max

1 0 0 1 / 5O / m i n

1 0 0 1 / 5 ' / a d e q

1 0 0 1 / 5O / max

7 . 1 s q . i n c h e s P e r c e n t i l e

1 . 7 5 s q . i n c h e s P e r c e n t i l e

2 5

0 . 0 8

2 . 9

4 8 . 5

1 . 0

3 1 . 4

3 3 5 . 0

0 . 1 7

6 . 7

1 5 0 . 0

0 . 5

1 8 . 8

4 3 2 . 0


7 5

0 .06

2 3 . 5

1 4 1 . 0

2 . 5

8 7 . 2

> 3 5 2 . 0

0 . 1 4

3 8 . 7

2 5 4 . 0

0 . 8

1 9 9 . 0

> 3 5 2 . 0

2 5

0 . 0 0 1

0 . 2 8

6 . 5

0 . 5

9 . 1

> 7 3 . 1

0 . 0 5

3 . 0

1 6 . 3

0 . 1 8

8 . 7

> 7 3 . 1

2 5

0 . 0 2

1 . 0

2 9 . 7

0 . 5

2 8 . 2

1 9 9 . 0

0 . 0 4

2 . 7

5 6 . 3

0 . 4

2 5 . 0

1 9 9 . 0

50

0.11

9 . 5

1 4 2 . 0

1 . 7

6 5 . 7

5 3 2 . 0

0 . 2 0

9 . 5

311 .0

1 . 0

6 5 . 7

6 4 1 . 0

50

0 .32

4 . 3

4 8 . 9

1 . 2

4 8 . 5

> 3 5 2 . 0

0 . 0 8

1 1 . 7

1 9 0 . 0

0 . 5

5 2 . 0

> 3 5 2 . 0

7 5

0 . 1 7

2 3 . 5

2 8 9 . 0

2 . 5

1 5 0 . 1

8 2 9 . 0

0 . 3 0

40 .0

4 8 5 . 0

1 . 7

3 1 1 . 0

8 2 9 . 0

50

0 .002

1 . 4

1 5 . 5

0 . 7

2 2 . 4

> 7 3 . 1

0 . 0 8

6 . 2

45 .6

0 . 4

3 5 . 3

> 7 3 . 1

75

0 . 0 0 3

2 . 6

3 5 . 3

2 . 1

3 5 . 3

> 7 3 . 1

0 . 0 9

2 1 . 5

> 7 3 . 1

0 . 6

> 7 3 . 1

> 7 3 , 1

TABLE 4 . 3 . DUSK MINIMUM, ADEQUATE, AND MAXIMUM CANDLE- POWER PERCENTILES FOR THREE LAMP DIAMETERS, TWO VIEWING DISTANCES, AND THREE FIXATION ANGLES. FIELD PILOT STUDY WITH 7 SUBJECTS

C o n d i t i o n

D i s t /Angles0 /Csr i ter im

N o t e : W h e n e v e r a v a l u e appears p r e c e d e d by > as i n >x, t h i s means n o r e s p o n s e had b e e n e l i c i t e d a t t h e maximum i n t e n s i t y o f t h e lamp a n d x i s t h e maximum v a l u e .

3 0 1 / O 0 / m i n

3 0 ' / 0 ° / max

3 0 1 / 1 5 ' / m i n

30'/ 1 5 ' / adeq

l o o ' / O 0 / m i n

l o o ' / O 0 / max

1 0 0 1 / 5 ' / m i n

l o o ' / 5 ' / adeq


2 5 5 0 7 5


2 5 5 0 7 5


2 5 5 0 7 5

0 . 0 4

2 7 . 0

0 . 2 2

4 . 7

0 . 0 8

9 8 . 0

0 . 4 7

9 . 4

0 . 2 3

1 1 7 . 0

0 . 4 0

1 2 . 9

0 . 4 0

1 4 1 . 0

0 . 7 8

2 3 . 0

0 . 0 1

1 3 . 0 2 6 . 0

0 . 0 7

2 . 7

2 1 . 5

0 . 0 8

9 . 0

0 . 9 4

1 9 6 . 0

1 . 3

1 0 9 . 0

3 . 0

3 9 1 . 0

3 . 8

5 0 . 0

0 . 0 5

0 . 1 4

2 0 . 0

0 . 0 3 0 . 1 3

4 4 . 2

0 . 3 3

2 6 . 0

0 . 0 8 0

3 1 . 8

0 . 1 2

4 6 . 0

0 . 1 4

6 9 . 0

0 . 4 7

4 7 . 0

0 . 0 0 3

1 . 5

0 . 0 3

1 . 7

0 . 4 9 0 . 0 1 7 0 . 0 3

1 4 . 2

0 . 0 1 9

9 . 9

0 . 2 1

9 0 . 0

2 . 2

1 2 7 . 0

9 8 . 0

2 . 3

3 5 . 0

0 . 0 0 6

3 . 2

0 . 0 5

6 . 0

3 4 . 0

0 . 1 6

2 7 . 1

TABLE 4.4. NIGHT M I N I M U M , ADEQUATE, AND MAXIMUM CANDLE- POWER PERCENTILES FOR THREE LAMP DIAMETERS, TWO V I E W I N G DISTANCES, AND THREE FIXATION ANGLES. LABORATORY STUDY DATA FOR 30 SUBJECTS

Note: Whenever a v a l u e a p p e a r s p r eceded by > a s i n >x, t h i s means no r e s p o n s e had been e l i c i t e d a t t h e maximum i n t e n s i t y o f t h e lamp and x i s t h e maximum v a l u e .

C o n d i t i o n

DistbngleO/Criterion

3 0 1 / 0 ° / min

3 0 1 / 0 ° / adeq

3 0 1 / 0° / max

3 0 1 / 1 5 0 / min

3 0 1 / 15O/ adeq

3 0 1 / 15O/ max

1 0 0 1 / 0 ° / min

1 0 0 1 / 0 ° / adeq

1 0 0 1 / 0 ° / max

1 0 0 1 / 5O/ min

1 0 0 1 / 5O/ adeq

1 0 0 1 / 5O/ max


25 5 0 75


25 50 7 5

0 . 0 1

0 . 6 3

28.2

0 . 0 4

4.0

51.6

0 .02

1 . 7

5 6 . 3

0 .03

4 .0

59 .4

0 . 0 0 3

0 .42

1 1 . 7

0 .02

2 .3

32 .5

0 . 0 0 8

1.3

29 .7

0 . 0 2

2 .3

3 4 . 4

0 .19 s q . i n c h e s P e r c e n t i l e

25 5 0 75

0 . 0 0 1

0 .35

7.6

0 .008

1.6

27.5

0 .005

0 .8

5 .9

0 .008

1 . 4

20.6

0 . 0 3

3 .4

110 .0

0 . 0 8

8.8

8 1 , 3 1 5 0 . 0

0 .03

6 .7

8 1 . 3 1 6 9 . 0

0 .04

7 .8

87.5

0 . 0 0 8

1 . 5

42.2

0 . 0 2 7

5 .5

54.5

0 , 0 1 3

2 .5

44.6

0 . 0 2 7

5 . 1

9 3 . 4

0 . 0 4

1 6 . 9

203.0

0 . 1 1

16.9

0 . 0 4

1 3 . 1

0 . 0 8

1 0 . 6

1 5 0 . 1

0 . 0 2 7

5 .5

8 2 . 1

0 .076

13 .3

9 3 . 4

0 . 0 2 7

6 .6

1 1 3 . 4

0 .027

2 3 . 5

1 6 8 . 0

0 . 0 0 3

1 . 9

29.7

0 . 0 1 8

3 .4

45.6

0 , 0 0 8

1 . 4

20.2

0 . 0 1 8

5.5

45 .7

0 . 0 1 8

3.9

7 3 . 1

0 .080

9.9

> 7 3 . 1

0 . 0 0 8

4.9

45.6

0 .023

35.3

,73.1

TABLE 4.5. NIGHT M I N I M U M , ADEQUATE, AND MAXIMUM CANDLE- POWER PERCENTILES FOR THREE LAMP DIAMETERS, TWO VIEWING DISTANCES, AND THREE FIXATION ANGLES. FIELD PILOT STUDY WITH 9 SUBJECTS

3 0 t / O 0 / min

3 0 t / O 0 / max

3 0 t / 15O / rnin

3 0 1 / 15' / max

1 0 0 t / O 0 / rnin

l o o ' / 0° / max

1 0 0 t / 5O / rnin

Note: Whenever a v a l u e a p p e a r s p r eceded by > as i n > x t h i s means no r e s p o n s e had been e l i c i t e d a t t h e maximum i n t e n s i t y o f t h e lamp a n d x i s t h e maximum v a l u e .

0.19 s q . i n c h e s P e r c e n t i l e

25 50 7 5

TABLE 4.6. 9 0 t h PERCENTILE M I N I M U M VISUAL THRESHOLDS ( I N CANDLES) I N DUSK AND DAY CONDITIONS FOR TWO LAMP DIAMETERS, TWO VIEWING DISTANCES, AND THREE FIXATION ANGLES

1 .75 s q . i n c h e s P e r c e n t i l e

25 50 75 Dist/ Angl eO/Criterion


2 5 50 75

Dusk Day

C o n d i t i o n ~ i s t / ~ n g l e O / M i n

301 / O 0 / min

301 / 15' / min

1 0 0 t / O 0 / m i n

1 0 0 t / 5O / min

7 . 1 sq. i n c h e s

21.9

110.0

70.0

109

1.75 s q . i n c h e s

9.0

80.8

16.2

79.5

7 .1 s q . i n c h e s

0 .2

7.8

0.38

2 . 1

1 .75 s q . i n c h e s

0.08

4 . 6

0.18

1.2

b r i g h t by 75 p e r c e n t of daytime s u b j e c t s whose viewing o r i e n t a t i o n

i s a t 15 degrees t o t h e l i g h t source ( i . e , , 367 cp; Table 4 . 1 )

would be t o o b r i g h t i n 0 degree dusk c o n d i t i o n s f o r over 75 per-

c e n t of d r i v e r s a t 30 f e e t and 50 p e r c e n t a t 100 f e e t (Tables

4 . 2 and 4 . 3 ) .

I n making compromises it i s u s e f u l t o cons ide r t h e f a c t o r s

t h a t a r e t o be weighed a g a i n s t each o t h e r . I t may be h e l p f u l t o

b r i e f l y d i s c u s s what it i s t h a t was measured by t h e exper imenta l

procedure d e s c r i b e d , Of t h e t h r e e t h r e s h o l d s computed, on ly t h e

a b s o l u t e (minimum) t h r e s h o l d i s n o t open t o widely va ry ing i n t e r -

p r e t a t i o n a c r o s s s u b j e c t s . What a s u b j e c t a s s e s s e s a s "adequate"

o r " o b j e c t i o n a b l e " i s a l e s s well d e f i n e d s u b j e c t i v e judgment,

and i s more d i f f i c u l t t o know how t o i n t e r p r e t i n t h e d r i v i n g

s i t u a t i o n , Indeed, i n a d i f f e r e n t phase (Task 2 ) of t h i s p r o j e c t

s u b j e c t s were a l s o asked t o i n d i c a t e t h e l e v e l of s i g n a l b r i g h t -

n e s s o b j e c t i o n a b l e t o them, b u t wi th i n s t r u c t i o n s t h a t s t r e s s e d

t h a t by o b j e c t i o n a b l e was n o t meant merely "no longer p e r f e c t l y

comfor table t o s t a r e a t . " Such i n s t r u c t i o n s were probably l a r g e l y

r e s p o n s i b l e f o r t h e cons ide rab ly h i g h e r i n t e n s i t i e s t h a t were

r e q u i r e d t o be judged o b j e c t i o n a b l e i n t h a t s tudy .

I t would probably be s a f e t o assume t h a t i n t e n s i t i e s r a t e d

o b j e c t i o n a b l e i n t h i s s tudy a r e r e a l l y b r i g h t enough. This

assumption i s based on t h e reasons d i s c u s s e d above and t h e f o l -

lowing a d d i t i o n a l c o n s i d e r a t i o n s . F i r s t , t h e s i d e t u r n s i g n a l ,

because it i s a t u r n s i g n a l , w i l l be on only i n t e r m i t t e n t l y and

f o r s h o r t p e r i o d s of t ime, Second, such a s i g n a l w i l l be

l o c a t e d on t h e v e h i c l e i n a p o s i t i o n t h a t w i l l n o t o f t e n be i n

t h e d i r e c t l i n e of v i s i o n of o t h e r d r i v e r s .

A s f o r t h e l e v e l s r e q u i r e d f o r a lamp t o be r a t e d objec-

t i o n a b l e ( o r " c e r t a i n l y adequate" ) a t p e r i p h e r a l viewing a n g l e s ,

a g lance a t Tables 4 . 1 through 4.5 shows t h a t it may be imprac t i -

c a l t o recommend 50th p e r c e n t i l e i n t e n s i t i e s . However, a d r i v e r

might be expec ted t o moni tor a r e a s t o t h e r i g h t and l e f t of h i s

d i r e c t i o n of motion. T h e r e f o r e , l e v e l s of s i g n a l i n t e n s i t y g r e a t

enough t o a t t r a c t h i s a t t e n t i o n a t p e r i p h e r a l v iewing a n g l e s ,

w h i l e i n h e r e n t l y d e s i r a b l e , shou ld be compromised w i t h t h e need

t o avo id g l a r e d i s c o m f o r t and d i s a b i l i t y which would occur i f

such i n t e n s i t i e s a r e encoun te red a l o n g t h e d i r e c t l i n e of s i g h t .

A p p l i c a t i o n of R e s u l t s . The recommendations a r e i n -

c luded i n T a b l e s 4 . 7 and 4 .8 . They do n o t i n c l u d e d a t a f o r t h e

0 .5- inch d i ame te r lamp f o r which complete r e s u l t s cou ld n o t b e

o b t a i n e d because of i n s u f f i c i e n t l i g h t o u t p u t w i t h such a

s m a l l opening. The t a b l e s c o n t a i n minimum and maximum candle-

power v a l u e s f o r bo th a d u a l i n t e n s i t y s i d e t u r n s i g n a l (Table

4 . 7 ) and a s i n g l e i n t e n s i t y system (Table 4 . 8 ) . The r ecomenda-

t i o n s a r e g iven f o r h o r i z o n t a l a n g l e s t h a t r a d i a t e from t h e s i d e

of t h e v e h i c l e a s i n F i g u r e 4 .10 . F igu re 4 . 1 0 r e p r e s e n t s a road

w i t h t h r e e l a n e s of t r a f f i c moving i n t h e same d i r e c t i o n . The

heavy l i n e l a b e l e d - T i n t h e diagram r e p r e s e n t s t h e l a t e r a l pos i -

t i o n a t which t h e s i d e t u r n s i g n a l cou ld be f o r a v e h i c l e a t t h e

0 - foo t p o s i t i o n i n l a n e 1, That i s , i f t h e t a r g e t v e h i c l e was a t

t h e l e f t extreme of l a n e 1 t h e s i g n a l would be a t t h e l e f t

ex t reme of l i n e - T , n e a r t h e p o i n t R , e t c . The d r i v e r s f o r whom

a s i d e t u r n s i g n a l on t h e t a r g e t v e h i c l e would be r e l e v a n t

a r e t h o s e n e a r l y a b r e a s t of - T i n bo th l a n e s 2 and 3 , and i n l a n e

2 f o r d i s t a n c e s e x t e n d i n g back t o o v e r 100 f e e t beh ind - T. The

heavy h o r i z o n t a l l i n e s l a b e l e d A and B r e p r e s e n t t h e p o r t i o n of

l a n e s 3 and 2 , r e s p e c t i v e l y , where t h e l a t e r a l eye p o s i t i o n s might

b e , of d r i v e r s i n t h o s e l a n e s who a r e e x a c t l y a b r e a s t of t h e t a r -

g e t s i g n a l a r e a T. - The f a r l e f t p o i n t o f l i n e A i s about 25 f e e t

from t h e f a r r i g h t p o i n t ( r ) of T. - Thus, a d r i v e r n e a r i n g s i g n a l

T a t a 9 0 deg ree a n g l e i s n o t l i k e l y t o be more t h a n 25 f e e t from - it. For any d i s t a n c e back i n l a n e 2 , a d r i v e r ' s l a t e r a l eye pos i -

t i o n a t t h a t d i s t a n c e w i l l , of c o u r s e , s t i l l f a l l i n t h e l a t e r a l

p o r t i o n of t h e l a n e co r r e spond ing t o l i n e B. Lines a r e p r o j e c t e d

TABLE 4.7. MINIMUM AND MAXIMUM INTENSITIES IN DAY AND NIGHT CONDITIONS FOR TWO LAMP AREAS, 5'-90' H LEFT OR RIGHT' , FOR A DUAL-INTENSITY, SIDE-MOUNTED, AMBER TURN SIGNAL^

Candlepower

Lamp Day Night

TABLE 4.8. MINIMUM AND MAXIMUM INTENSITIES FOR TWO LAMP AREAS, 5'-90' H LEFT OR RIGHT', FOR A SINGLE INTENSITY, SIDE-MOUNTED , AMBER TURN SIGNAL

Area (sq. inches)

7.1

l~arn~ H-V is parallel to the long axis of the vehicle, facing forward.

Horizontal Angle

5'-15'

Lamp

2~ntensities at degrees up (U) or down (D) from H should be in proportion to those shown at H in SAE 5-914 (1965).

Area (sq. inches)

7.1

Min Max

150 297

Min Max

2.1 56

Horizontal Angle

5'-15'

Candlepower Min Max

56 150

Lane 3

----- r F I '

Lane 2

--2-

T Lane 1

100 9 0 80 7 0 6 0 50 4 0 3 0 2 0 10 0

Distance From T (Feet)

F i g u r e 4.10. The e f f e c t of d i s t a n c e upon a n g u l a r v i s i b i l i t y of s i d e mounted t u r n s i g n a l s .

straight down lane 2 from the outer edges of line B and at some

angle a (0°<a<900) from the outer edges of line - T (points R and r). The area intercepted by such lines of projection would constitute

the area in lane 2 in which the eye position of a driver in that

lane would be at an angle a to a signal located at some point

along line - T, Areas I and I1 in Figure 4,10 were formed by such

a process, letting a=15' and 5' respectively. Thus, to be at a

visual angle of 15 degrees to T, a driver in lane 2 must be - between 25 and 57 feet from - T. To view T at a 5 degree angle, - he must be from 70 to 160 feet behind T. -

Since a driver viewing - T at less than 15 degrees is likely to be at a distance closer to the 100 foot test distance of the

present study, and when viewing - T at greater than 15 degrees is more likely to be at a viewing distance similar to the 30 foot

condition, the intensity recommendations in Tables 4,7 and 4.8

are dichotomized at the 15 degree angle. Recommendations for

radial angles of 5 degrees to 15 degrees are based on the test

data collected at 100 feet; whereas those for angles of 15'-90'

are based on the 30-foot data.

Table 4,7 shows recommended minimum and maximum intensity

values as a function of lamp area for the day (off) and night

(on) position of the headlight switch.

A criterion of 75th percentile, day, adequate intensity at

the relevant distance and peripheral viewing angles of 5 degrees

or 15 degrees was taken to determine daytime maxima, The 5'-15'

values were obtained from the 100-foot/5' data, and the 15'-90'

values from the 30-foot/15' data in Table 4.1, For example,

the 5'-15' day maximum value for the 7.1 square inch lamp is

the 75th percentile value for the 100 foot/5' adequacy data (297

cp) in Table 4.1.

The daytime minimum criterion was the intensity which was

considered objectionable by not more than 25 percent of subjects

at dusk when the lamp was viewed directly at 0 degrees, at 100

and 30 feet for the 5'-15' and 15'-90' horizontal angles, respec-

tively. For example, the 15'-90' day, minimum intensity for

the 1-75 square inch lamp is the dusk, 25th percentile,

objectionable (maximum) value (29.7 cp) for the 30 foot/OO data

in Table 4.2.

The night maximum intensity criterion was the intensity

which was objectionable to not more than 25 percent of subjects

at night when viewing the lamp directly at 0 degrees at 100

and 30 feet for the 5'-15' and 15'-90' horizontal angles, respec-

tively. For example, the 15'-90° night maximum intensity for

the 7.1 square inch lamp is the night, 25th percentile, objection-

able (maximun) value (28.2 cp) for the 30 foot/OO data in Table

4.4.

The night minimum intensity criterion was the intensity at

which the lamp was just visible at dusk for 90 percent of sub-

jects when viewed at 100 feet and 5 degrees, 30 feet and 15 de-

grees, for the 5'-15' and 15'-30' horizontal angles, respectively.

For example, the 5'-15' night minimum intensity for the 1.75

square inch lamp, is the 90th percentile visibility threshold

(1.2 cp) at 100 feet, 5 degrees shown in Table 4.6. The dusk

data were used as a criterion condition to ensure visibility at

the higher ambient intensity of the night-dusk continuum.

Table 4.8 shows suggested horizontal intensity minima and

maxima for a single intensity side-turn signal. The minimum

intensities are the night maxima, and the maximum intensities

are the day minima of the corresponding dual intensity conditions

in Table 4.7.

The values in Table 4.8 are only one possible compromise

between daytime visibility and nighttime glare effects, and show

quite clearly that an adequate solution is not possible with a

single intensity level. The use of an intensity between the mini-

mum and maximum values of Table 4.8 will result in a signal that causes more discomfort at night and gives less adequate visibility

in the day than a signal from the corresponding dual intensity

sys tem.

5 , A mTHODOLOGY FOR STUDYING THE EFFECT OF IMPROVED REAR LIGHT- ING CONFIGURATIONS ON HIGHWAY SAFETY (TASK 5)

INTRODUCTION.

P r i n c i p l e s Of Ana lys i s . Highway S a f e t y , and any improvements

i n highway s a f e t y , i s one measure of t h e performance of a complex

i n t e r a c t i v e sys tem which c o n t a i n s t h e o p e r a t o r , t h e v e h i c l e , and

t h e environment a s i t s p r i n c i p a l components. T h e r e f o r e , it i s

ex t r eme ly i m p o r t a n t t h a t t h e e f f e c t s of any improvement be i s o l a t e d ,

a s much a s p o s s i b l e , from t h e e f f e c t s of o t h e r components. Th i s

r e q u i r e s t h a t t h e sys tem t o be modi f ied b e ana lyzed b e f o r e it i s

e v a l u a t e d .

The e f f e c t s of any change which improves highway s a f e t y - - i . e . ,

which r educes t h e number and s e v e r i t y of c rashes- -proceeds from

t h e change through an i n c o m p l e t e l y d e f i n e d c a u s a l c h a i n t o t h e

u l t i m a t e improvement, T h e r e f o r e , it i s n a i v e t o a t t e m p t t o r e l a t e

any change d i r e c t l y t o a r e d u c t i o n i n t h e number of a c c i d e n t s w i th -

o u t c o n s i d e r i n g bo th t h e i n t e r m e d i a t e l i n k s i n t h e c a u s a l c h a i n

and o t h e r v a r i a b l e s which may modify t h e s e l i n k s . F i g u r e 5 . 1 i s

a s chema t i c s k e t c h of a highway s a f e t y subsystem which d e s c r i b e s

t h e e f f e c t of improved r e a r l i g h t i n g sys tems on c r a s h r e d u c t i o n .

I t i s i m p o r t a n t t o n o t e t h e l a r g e number of a d d i t i o n a l v a r i a b l e s

a f f e c t i n g t h e r e s u l t s a t each s t e p i n t h e c a u s a l c h a i n . Unless

t h e s e f a c t o r s a r e c o n t r o l l e d t h e e f f e c t of improvements i n l i g h t -

i n g systems can b e e a s i l y o v e r s t a t e d .

I n t h e s chema t i c diagram two p o t e n t i a l e f f e c t s of improved

l i g h t i n g sys tems a r e i n d i c a t e d :

(1) I n t h e normal d r i v i n g s i t u a t i o n , i n f o r m a t i o n s u p p l i e d

t o t h e d r i v e r e n a b l e s him t o avo id c r i t i c a l o r emergency s i t u a t i o n s .

( 2 ) Once t h e d r i v e r becomes i n v o l v e d i n an emergency s i t u a -

t i o n , t i m e l y i n f o r m a t i o n can h e l p him avo id a c r a s h .

I n an e a r l i e r s t u d y , Nickerson e t a l . , ( 1 9 6 8 ) d e a l t w i t h t h e

f i r s t e f f e c t . They found t h a t , "The ca r - fo l lowing t a s k i n v o l v e s

m a i n t a i n i n g a d e s i r e d headway and v e l o c i t y i n t h e p re sence of d i s -

t u r b a n c e s . . . " HSRI h a s been i n v e s t i g a t i n g t h e second e f f e c t :

how improved r e a r l i g h t i n g sys tems a f f e c t t h e d r i v e r ' s r e sponse

1r.formation from Rear Llghtlng System (Signal System Deslgn)

Environment iieather Speed Environment

Slgnal Systern

Figure 5.1. Schematic representation showing the effect of rear lighting system design on highway safety.

Deslgn Informat~on b fronl Rear ~ i ~ h t ~ ~ system NOR'1AL DRIVIYG

RESPONSE TO CRITICAL SITUATION

Other Lights Other Infornlat~on Characteristics - Slgns, Itoad Reaction Tlrne \ la rk lngs Attentiveness Perception &

*dther Surlsory *Evaluation of aisk Processing of +-- Drlver Characteristics

lnputs eInterpretatlon of Information Road Condition

*Alcohol T

t o c r i t i c a l emergency d r i v i n g c o n f l i c t s . An emergency d r i v i n g

c o n f l i c t i s d e f i n e d a s a d r i v i n g s i t u a t i o n i n which a r a p i d

t u r n i n g o r b rak ing maneuver must be performed i n o r d e r t o avoid

a c rash . I n p a r t i c u l a r , a ca r - fo l lowing emergency has been

s t u d i e d . I n t h i s s i t u a t i o n , a l e a d c a r s t o p s suddenly and t h e

fo l lowing c a r must r e a c t t o t h e brake l i g h t s i g n a l and e i t h e r

s t o p o r c r a s h i n t o t h e l e a d c a r .

METHODOLOGY. The e v a l u a t i o n of a change i n a highway sys -

tem component can be t r e a t e d a s a comparison between two h i g h l y

r e l a t e d t r a f f i c subsystems t o determine t h e change i n c r a s h prob-

a b i l i t y fo l lowing t h e i n t r o d u c t i o n of t h e changed component a s

fo l lows :

AP - o v e r a l l change i n t h e p r o b a b i l i t y of c r a s h ; i f t h i s

change i s n e g a t i v e , an improvement has been made.

Po - t h e p r o b a b i l i t y of a c r a s h o c c u r r i n g w i t h i n t h e t r a f f i c

subsystem before a change.

P1 - t h e p r o b a b i l i t y of c r a s h w i t h i n t h e t r a f f i c subsystem

a f t e r a change.

The t r a f f i c subsystem i s d e f i n e d a s a s e t having N d i f f e r -

e n t t r a f f i c s i t u a t i o n s a s s u b s e t s o r e lements . Some examples of

t h e s e s u b s e t s a r e :

(1) A v e h i c l e moving i n an u n r e s t r i c t e d s t a t e on a s t r a i g h t

road.

( 2 ) A ca r - fo l lowing s i t u a t i o n i n which t h e l e a d v e h i c l e i s

moving i n an u n r e s t r i c t e d s t a t e .

( 3 ) A ca r - fo l lowing s i t u a t i o n i n which t h e l e a d v e h i c l e

suddenly makes an emergency s t o p .

( N ) An emergency s t o p on a wet road.

Each of t h e s e s u b s e t s c o n t a i n s e lements de f ined by s p e c i f i c

parameter v a l u e s . For example, t h e fo l lowing e lements would be

con ta ined i n s u b s e t 1 above:

a . Vehicle moving a t 30 mph on a g r a v e l road.

b. Vehicle moving a t 40 mph on an a s p h a l t road.

c , Vehic le moving a t 50 mph on a c o n c r e t e road.

1 2 1

S i n c e t h e t r a f f i c subsystem o p e r a t e s c o n t i n u o u s l y it i s

n e c e s s a r y t o impose a t ime dimension, ti, on each of t h e s e s i t u a -

t i o n s . Th i s dimension, which w i l l be s p e c i f i c f o r e a c h e v e n t

c o n s i d e r e d , c o v e r s t h e time from t h e d e f i n e d beginning of t h e

e v e n t under c o n s i d e r a t i o n u n t i l i t s d e f i n e d end. Using t h e ana ly-

s i s d e s c r i b e d above t h e p r o b a b i l i t y of a c r a s h o c c u r r i n g w i t h i n

t h e t r a f f i c subsystem can be exp res sed a s :

Ai - t h e pe rcen tage of t h e t o t a l t r a f f i c subsystem t h a t

c o n s t i t u t e s a s u b s e t d e f i n e d by s i t u a t i o n i.

Pi - t h e p r o b a b i l i t y of a c r a s h o c c u r r i n g w i t h i n s u b s e t i.

I f s e t I c o n t a i n s Mi d i s c r e t e e v e n t s , then :

where Ci i s t h e number of c r a s h e s o c c u r r i n g i n s e t i. I n g e n e r a l ,

The concept denoted by Ai i s i l l u s t r a t e d i n F igu re 5.2. I f an

improvement, i . e . , a r e d u c t i o n i n t h e number of c r a s h e s , can be

ach ieved i n s i t u a t i o n i , an improvement t o t h e t o t a l subsystem

r e s u l t s .

A mathemat ica l model can be c o n s t r u c t e d f o r each of t h e sub-

sets d e f i n e d by a p a r t i c u l a r s i t u a t i o n and t h e e v e n t s o c c u r r i n g

w i t h i n t h e s e s u b s e t s can b e r e p r e s e n t e d i n t h e model by p a r t i -

c u l a r parameter v a l u e s . For example, a model, developed by t h e

a u t h o r , of a ca r - fo l lowing s i t u a t i o n i n which t h e l e a d c a r makes

a sudden s t o p u s e s t h e laws of motion and t h e pa rame te r s l i s t e d

below t o d e f i n e s p e c i f i c e v e n t s :

(1) V e l o c i t y of l e a d c a r ( f p s )

( 2 ) V e l o c i t y of f o l l o w i n g c a r r e l a t i v e t o l e a d c a r ( f p s ) 2

( 3 ) Braking a c c e l e r a t i o n f o r bo th c a r s ( f p s )

( 4 ) Headway ( s e c )

( 5 ) P e r c e p t i o n and r e a c t i o n t i m e o f fo l lowing-ca r d r i v e r ( s e c )

J T o t a l T r a f f i c Subsystem

0' T r a f f i c S i t u a t i o n i t 1

/ T r a f f i c S i t u a t i o n i

- c - The e v e n t a non-crash c - The e v e n t a c r a s h

F i g u r e 5 . 2 . Schematic r e p r e s e n t a t i o n of t h e t r a f f i c subsys tern.

Obviously o t h e r parameters could be used i n a d d i t i o n t o t h e s e .

For a given s e t of parameter va lues it i s p o s s i b l e t o determine

whether o r n o t a c rash w i l l occur . A f u r t h e r s o p h i s t i c a t i o n

would be t o determine whether o r n o t a c r a s h of a given v e l o c i t y

w i l l occur . For t h e Mi e v e n t s of s e t i d e f i n e :

Ck =[ 0 i f a c r a s h d i d n o t occur 1 i f a c rash occurred

However, i n o r d e r t o determine Pi it i s necessary t o know t h e

p r o b a b i l i t y t h a t an even t r e s u l t i n g i n a c r a s h w i l l occur wi th in

s u b s e t i. I f a p a r t i c u l a r element , k, of t h e s u b s e t , i , i s de f ined

by r parameters then t h e p r o b a b i l i t y of t h i s element i s

where P i s equa l t o t h e p r o b a b i l i t y of parameter j occur r ing a t k j

l e v e l k. A s i n d i c a t e d p rev ious ly , t h e even t Ck has a va lue of 1

( i n d i c a t i n g c r a s h ) o r 0 ( i n d i c a t i n g no c r a s h ) . I t i s now p o s s i b l e

t o d e f i n e

I f a change occurs i n Pi a s a r e s u l t of a modi f i ca t ion i n t h e t r a f -

f i c subsystem t h e modi f i ca t ion can be eva lua ted i n terms of t h e

magnitude of t h e change it produces i n Pi. S ince M. i s ve ry l a r g e 1

it i s n o t reasonable t o compute Pi d i r e c t l y . However, a random

sample of Mi even t s could be used t o e s t i m a t e t h e va lue of Pi. A

s imula ted random sample of even t s can be ob ta ined by randomly

s e l e c t i n g va lues f o r each of t h e parameters j from t h e i r d i s t r i -

bu t ion i n t h e t r a f f i c s i t u a t i o n i. Thus, i f p r o b a b i l i t y d i s t r i -

b u t i o n s f o r each parameter can be o b t a i n e d , i t w i l l be p o s s i b l e

t o c o n s t r u c t a number of random elements k of t h e s e t i. The

summation of t h e p r o b a b i l i t y of t h e s e e v e n t s m u l t i p l i e d by Ck

provides an e s t i m a t e of Pi.

Many of t h e s e parameter d i s t r i b u t i o n s have been developed

through r e s e a r c h on o t h e r highway problems. For example, Dawson

and Chimini (1968) have developed a p r o b a b i l i t y d i s t r i b u t i o n of

headways i n s i n g l e - l a n e t r a f f i c f low, and Tignor (1968) has d e t e r -

mined t h e minimum s topp ing d i s t a n c e s f o r a sample of c a r s s e l e c -

t e d from a busy highway.

I n g e n e r a l , i f a component change can be expressed i n terms

of one o r more of t h e parameters of a model, it can be eva lua ted .

This procedure r e q u i r e s t h a t Pi be computed b e f o r e and a f t e r t h e

change and a p p r o p r i a t e parameter m o d i f i c a t i o n s a r e made.

I t i s impor tan t t o r e a l i z e what t h e e v a l u a t i o n s r e s u l t i n g

from t h i s procedure r e a l l y mean. We have proposed t h a t c e r t a i n

changes i n t h e highway system can be e v a l u a t e d by s tudy ing t h e i r

performance i n t h e r e s o l u t i o n of t r a f f i c c o n f l i c t s . S ince t h e

types of c o n f l i c t s cons ide red occur i n f r e q u e n t l y ( r e l a t i v e t o t h e

t o t a l number of v e h i c u l a r mi les t r a v e l e d ) it i s n o t f e a s i b l e t o

s t u d y c o n f l i c t r e s o l u t i o n by obse rv ing a c t u a l t r a f f i c , and e x p e r i -

mental a n a l y s i s would be dangerous and expensive . F i n a l l y , even

i f such o b s e r v a t i o n s were f e a s i b l e , many component changes should

be e v a l u a t e d b e f o r e t h e y a r e in t roduced i n t o t h e v e h i c u l a r t r a f f i c

system. For t h e s e r e a s o n s , models r e p r e s e n t i n g t r a f f i c c o n f l i c t s

a r e u s e f u l i n e v a l u a t i n g any change i n c r a s h p r o b a b i l i t y r e s u l t i n g

from changing a system component,

I t should be emphasized t h a t t h e c r a s h p r o b a b i l i t i e s ca lcu-

l a t e d r e f e r on ly t o those s i t u a t i o n s r e p r e s e n t e d by t h e model.

To t h e e x t e n t t h a t t h e model o p e r a t e s l i k e t h e r e a l wor ld , mean-

i n g f u l p r o b a b i l i t i e s w i l l be ob ta ined . S ince e f f e c t i v e simula-

t i o n models have been developed f o r a g r e a t v a r i e t y of problems,

t r a n s l a t i o n from t h e model t o t h e r e a l world should n o t be i n s u r -

mountable.

This e v a l u a t i o n p rocess does n o t i d e n t i f y t h e most c r i t i c a l

c a t e g o r i e s of t r a f f i c c o n f l i c t s w i t h i n t h e e n t i r e t r a f f i c system

( i .e . i t does n o t answer such q u e s t i o n s a s , "Do c r i t i c a l c a r -

fo l lowing s i t u a t i o n s occur more o f t e n than c r i t i c a l emergency-

t u r n i n g s i t u a t i o n s ? " ) , Decis ions of t h i s t y p e r e q u i r e competent

judgment, However, t h i s t echn ique pe rmi t s conc lus ions such a s :

"This component change reduces c r a s h p r o b a b i l i t y g iven t h e fo l low-

i n g t r a f f i c s i t u a t i o n . "

Monte Car lo S imula t ion . Using t h e b a s i c approach d e s c r i b e d

above, a model of t h e emergency ca r - fo l lowing s i t u a t i o n has been

developed and programmed f o r HSRI's IBM 1130 d i g i t a l computer.

This model has been imbedded i n a computer program which perfoms

a Monte Car lo s i m u l a t i o n of s i t u a t i o n s d e f i n e d by t h e model w i t h

t h e fo l lowing parameters :

(1) Dr ive r s i g n a l - p e r c e p t i o n time ( s e c . )

( 2 ) Braking a c c e l e r a t i o n ( f t . / s e c . 2 ,

( 3 ) Headway ( s e c . )

( 4 ) Ve loc i ty of fo l lowing c a r ( f t . / s e c . )

( 5 ) Ve loc i ty of l e a d c a r r e l a t i v e t o t h e fo l lowing c a r ( f t . / s e c . )

I n a d d i t i o n it i s p o s s i b l e t o s p e c i f y t h e maximum c o e f f i c i e n t

of road f r i c t i o n and t h e t ime r e q u i r e d f o r t h e d r i v e r t o move h i s

f o o t from t h e a c c e l e r a t o r t o t h e b rake peda l .

The model uses t h e b a s i c laws of motion and average d e c e l e r a -

t i o n s t o de termine whether o r n o t a c r a s h w i l l occur given a s p e c i -

f i e d s i t u a t i o n . The c o n f l i c t i s d e f i n e d by randomly s e l e c t e d v a l u e s

f o r t h e parameters mentioned above and t h e assumption t h a t t h e l e a d

c a r makes an emergency s t o p . One i n t e r e s t i n g m o d i f i c a t i o n uses

Hoffman's (1968) s t u d y t o e s t a b l i s h a minimum p e r c e p t i o n t ime f o r

v e h i c l e s c l o s i n g above a c r i t i c a l r a t e .

The remaining q u e s t i o n t o be answered i s , "How a r e t h e para-

meters f o r d e f i n i n g a p a r t i c u l a r s i t u a t i o n s e l e c t e d ? " T i g n o r ' s ( 1 9 6 8 ) data show t h e cumulat ive d i s t r i b u t i o n of b rak ing c a p a b i l i -

t i e s . One can l o c a t e any number from 0 . 3 1 t o 1.00 on t h e

o r d i n a t e and r ead a c r o s s t o t h e cu rve , t h u s o b t a i n i n g a c o r r e s -

ponding brake d e c e l e r a t i o n . I f t h e number used was chosen a t

random, t h e brake d e c e l e r a t i o n w i l l a l s o be random and i t can then

be used t o d e f i n e a randomly s e l e c t e d v e h i c l e i n a randomly s e l e c t e d

t r a f f i c c o n f l i c t .

A g r e a t d e a l has been w r i t t e n about computer-generated random

numbers (Hammersley and Handscomb, 1965) . S ince random number gen-

e r a t o r s used i n d i g i t a l computers a r e a n a l y t i c a l and t h u s n o t t r u l y

random, t h e term pseudo-random i s more a p p r o p r i a t e . However, f o r

our purpose t h e s e pseudo-random numbers behave adequa te ly a s random

numbers, I t i s impor tan t t h a t each v a l u e from 1 t o 1 0 0 have an

e q u a l chance of o c c u r r i n g , a c o n d i t i o n t h a t i s s a t i s f i e d by t h e

random-number g e n e r a t o r used. Thus, t h e parameter va lues w i l l be

s e l e c t e d i n p r o p o r t i o n t o t h e i r d i s t r i b u t i o n i n t h e popu la t ion ,

For a complete d i s c u s s i o n of t h i s approach t h e r e a d e r i s r e f e r r e d

t o S a s i e n i , e t a l e (1963) .

I n p u t parameters 1, through 5 , above, a r e d e f i n e d by means of

p r o b a b i l i t y d i s t r i b u t i o n s , These d i s t r i b u t i o n s a r e r ead d i r e c t l y

i n t o t h e program o r genera ted by means of t h e o r e t i c a l p r o b a b i l i t y

d i s t r i b u t i o n s . Values a r e randomly s e l e c t e d from each of t h e d i s -

t r i b u t i o n s i n o r d e r t o d e f i n e a s p e c i f i c emergency c o n f l i c t . Then

us ing t h e model, computations a r e performed t o determine whether

o r n o t a c r a s h would occur , By o p e r a t i n g t h e model a l a r g e number

of t imes ( e . g . , N = 1 0 0 0 ) it i s p o s s i b l e t o determine t h e p e r c e n t

occurrence of c r a s h e s having d i f f e r e n t v e l o c i t i e s . I n t h i s manner,

Monte Car lo s i m u l a t i o n e n a b l e s t h e r e s e a r c h e r t o determine t h e

p r o b a b i l i t y of c r a s h e s f o r t h e s i t u a t i o n d e f i n e d by t h e model and

t h e p r o b a b i l i t y d i s t r i b u t i o n s of t h e parameters . This technique

i s analogous t o s e v e r a l y e a r s of obse rv ing emergency t r a f f i c con-

f l i c t s i n which t h e components be ing e v a l u a t e d a r e w e l l de f ined .

The fo l lowing o u t p u t s a r e p r e s e n t l y genera ted:

1, ~ i s t r i b u t i o n of v e l o c i t y a t c r a s h

2 . D i s t r i b u t i o n of t ime t o c r a s h

3. D i s t r i b u t i o n of d i s t a n c e t o c r a s h

One measurement o b t a i n a b l e from t h e s i m u l a t i o n model i s t h e

pe rcen tage of c r a s h e s o c c u r r i n g w i t h i n each s e t of assumptions.

However, we b e l i e v e t h a t it i s a l s o impor tant t o compare c r a s h

s e v e r i t y , s i n c e t o t a l l o s s due t o highway c r a s h e s i s t h e product

of t h e number of c r a s h e s and t h e l o s s p e r c r a s h . There fo re , reduc-

t i o n i n c r a s h s e v e r i t y i s a s impor tan t a s r e d u c t i o n i n number of

c r a s h e s ; i . e . , an improvement t h a t changes f a t a l c r a s h e s t o non-

f a t a l c r a s h e s i s more impor tan t than an improvement t h a t changes

n o n f a t a l c r a s h e s t o noncrashes. The c r i t e r i o n chosen f o r compar-

i n g a l t e r n a t i v e systems i s a cumulat ive frequency d i s t r i b u t i o n of

c r a s h e s o c c u r r i n g a t o r below a given v e l o c i t y .

D e s c r i p t i o n of Model. The model i s designed t o r e p r e s e n t a

s i t u a t i o n i n which two v e h i c l e s a r e i n i t i a l l y fo l lowing each o t h e r

a t d e f i n e d headway and v e l o c i t i e s . The d r i v e r of v e h i c l e A ( t h e

l e a d v e h i c l e ) suddenly a p p l i e s t h e b rakes , t h u s a c t i v a t i n g h i s

b rake l i g h t , The d r i v e r of v e h i c l e B ( t h e fo l lowing v e h i c l e ) must

p e r c e i v e t h e b r a k e - l i g h t s i g n a l and apply h i s v e h i c l e brakes . The

assumption t h a t t h e fo l lowing v e h i c l e w i l l b rake was used because

it i s b e l i e v e d t h a t most d r i v e r s w i l l a t t empt t o brake r a t h e r

than t u r n when faced wi th a c r i t i c a l emergency. This i s somewhat

suppor ted by a s tudy of an automobile s i m u l a t o r conducted by

B a r r e t , e t a l . , (1968) i n which on ly one o u t of e l e v e n d r i v e r s

r e a c t e d t o a s imula ted emergency by t u r n i n g . This d r i v e r was a l s o

an a i r p l a n e p i l o t which might e x p l a i n h i s p a r t i c u l a r r e a c t i o n ,

The fo l lowing p o s s i b l e occurrences can r e s u l t from t h i s emergency:

1. Vehic le B s t r i k e s v e h i c l e A a f t e r v e h i c l e B has begun

b rak ing .

a . Vehic le A i s moving

b. Vehic le A i s n o t moving

2 . Vehic le B s t r i k e s v e h i c l e A p r i o r t o t h e t ime v e h i c l e B

has begun b rak ing .

a . Vehic le A i s moving

b. Vehic le A i s n o t moving

3 , Vehic le B does n o t s t r i k e v e h i c l e A

The model computes t h e t ime f o r v a r i o u s s t a g e s beginning wi th

i n i t i a l brake a p p l i c a t i o n through t h e p o i n t a t which e i t h e r a c r a s h

occurs o r both v e h i c l e s s t o p . A l l t imes a r e computed us ing t h e

b a s i c laws of motion and s e l e c t e d parameter v a l u e s , The model

p r e s e n t l y uses average brake d e c e l e r a t i o n va lues . This i s n o t

cons idered t o be a s e r i o u s d e f i c i e n c y s i n c e t h e comparison i s

between d i f f e r e n t r e a r l i g h t i n g c o n f i g u r a t i o n s i n t h e con tex t of

t h e same c r i t i c a l s i t u a t i o n ,

Procedure For Appl ica t ion Of The Model To Rear L igh t ing

System Eva lua t ion . The use of t h e model desc r ibed above t o evalu-

a t e d i f f e r e n t r e a r l i g h t i n g c o n f i g u r a t i o n s r e q u i r e s t h a t pe rcep t ion

t i m e d i s t r i b u t i o n s be a v a i l a b l e f o r each c o n f i g u r a t i o n s t u d i e d . I n

a d d i t i o n it i s necessa ry t o d e s c r i b e t h e emergency c o n f l i c t s by

means of p r o b a b i l i t y d i s t r i b u t i o n s of o t h e r impor tant parameters .

The parameters used i n t h i s model have been de f ined p rev ious ly .

Through proper s e l e c t i o n of t h e d i s t r i b u t i o n s it i s p o s s i b l e t o

compare d i f f e r e n t l i g h t i n g c o n f i g u r a t i o n s w i t h i n s e v e r a l de f ined

emergencies. The q u e s t i o n of which emergencies occur most f r e -

q u e n t l y has n o t been completely answered. However we a r e a t tempt-

i n g t o s e l e c t a s e t of s i t u a t i o n s which appears most l i k e l y t o

f a l l w i t h i n a most f r e q u e n t s e t given our p r e s e n t in fo rmat ion ,

By making t h e s e comparisons over a l l of t h e most f r e q u e n t emer-

genc ies we expec t t o o b t a i n a r o b u s t comparison of t h e v a r i o u s

l i g h t i n g c o n f i g u r a t i o n s .

The fo l lowing sources of informat ion have been used t o d e f i n e

emergencies:

1. Percep t ion t ime d a t a from t h e exper imenta l s t u d i e s con-

ducted i n o t h e r phases of t h i s p r o j e c t . These s t u d i e s

provide a time va lue f o r t h e pe r iod from brake app l i ca -

t i o n of l e a d v e h i c l e t o s t a r t of f o o t movement from

a c c e l e r a t o r t o brake f o r t h e d r i v e r of t h e fo l lowing

v e h i c l e , These s t u d i e s and ano the r (Mortimer, 1969b) were

conducted under both urban and r u r a l d r i v i n g cond i t ions .

A s e p a r a t e va lue f o r moving f o o t from a c c e l e r a t o r t o brake

i s used.

2 . T ra f f i c - f low s t u d i e s conducted by Joseph L. T r e i t e r e r

(1966) of Ohio S t a t e Un ive r s i ty have provided v e l o c i t y ,

r e l a t i v e v e l o c i t y between a d j a c e n t v e h i c l e s , and head-

way measurements. He used photogrammetric techniques t o

o b t a i n t h e measurements on an expressway nea r Columbus,

Ohio, du r ing an e a r l y morning rush hour .

3. A d i s t r i b u t i o n of d r i v e r - v e h i c l e b rak ing c a p a b i l i t y was

ob ta ined from a s tudy conducted by S.C. Tignor (1968) of

B . P . R . He measured t h e s t o p p i n g d i s t a n c e under emergency

s topp ing c o n d i t i o n s f o r a number of v e h i c l e s pass ing a

p a r t i c u l a r p o i n t on a highway. His d i s t r i b u t i o n of s top -

p ing d i s t a n c e s was conver ted t o a d i s t r i b u t i o n of b rak ing

d e c e l e r a t i o n .

4. Speed d i s t r i b u t i o n s measured by t h e Michigan S t a t e Highway

Department (1968) have been used t o r e p r e s e n t speeds on

two-lane s t a t e highways,

5 , A headway d i s t r i b u t i o n model developed by Dawson and

Chimini (1968) has been used t o r e p r e s e n t headways i n

s i n g l e - l a n e t r a f f i c s i t u a t i o n s . This model, known a s

t h e Hyperlang Model, assumes t h a t t r a f f i c flow i s made

up of c o n s t r a i n e d v e h i c l e s and uncons t ra ined v e h i c l e s .

I t uses a weighted combination of an exponen t i a l d i s t r i -

b u t i o n (uncons t r a ined flow) and an Er lanq d i s t r i b u t i o n

( c o n s t r a i n e d f low) t o r e p r e s e n t t h e highway s i t u a t i o n ,

A s t h e number of v e h i c l e s p e r hour i n c r e a s e s t h e pe rcen t -

age of cons t ra ined-f low v e h i c l e s a l s o i n c r e a s e s . This

model has been found t o ag ree ve ry w e l l w i t h d a t a pre-

s e n t e d i n t h e 1965 Highway Capaci ty Manual and wi th d a t a

ob ta ined by Purdue Unive r s i ty (1967) . Determinat ion of S i g n i f i c a n t Di f fe rences . S ince each simu-

l a t e d emergency c o n f l i c t i s independent of a l l o t h e r s it i s p o s s i b l e

t o apply t h e Chi-square t e s t t o determine whether o r n o t p a r t i c u l a r

s i t u a t i o n s have s i g n i f i c a n t l y fewer c ra shes . Each i n d i v i d u a l con-

f l i c t can be t r e a t e d a s a s i n g l e experiment i n which a c rash occurs

o r does n o t occur . The Chi-square tes t can be used t o determine

i f t h e p e r c e n t of c rashes under s i t u a t i o n 1 i s s i g n i f i c a n t l y d i f -

f e r e n t from t h e pe rcen t of c rashes under s i t u a t i o n 2 . The computa-

t i o n of Chi square i s a s fo l lows (Bowker and Lieberman, (1963):

2 x = Chi square

El - Number of c rashes occur r ing i n s i t u a t i o n 1.

5 - Number of non-crashes occur r ing i n s i t u a t i o n 1

E2 - Number of c r a s h e s occur r ing i n s i t u a t i o n 2

E2 - Number of non-crashes occur r ing i n s i t u a t i o n 2

I f w e perform N obse rva t ions of each s i t u a t i o n t h e above express ion

can be g e n e r a l i z e d i n terms of p ropor t ions P1 and P 2 .

P1 - Percentage of c r a s h e s i n s i t u a t i o n 1

P2 - Percentage of c r a s h e s i n s i t u a t i o n 2

Chi square can then be expressed a s kollows:

2 - (P2N - PIN) 2 2

X - t ([l - P2]N - 11 - P1lN)

PIN (1 - P , ) N

AP - Dif fe rence between p e r c e n t c r a s h e s

Each s i t u a t i o n was s i m u l a t e d 1000 times and t y p i c a l v a l u e s

f o r Pl a r e between . 4 0 and .60. For a s i g n i f i c a n c e l e v e l of

a = .05 t h e a p p r o p r i a t e Chi s q u a r e v a l u e i s 3.84. By u s i n g t h e s e

v a l u e s it i s p o s s i b l e t o compute a minimum d i f f e r e n c e c o n s i d e r e d

s i g n i f i c a n t .

Th i s v a l u e f o r AP i s approx ima te ly t h e same o v e r t h e r ange o f

obse rved P l ' s . Thus, it (Apmin = . 03 ) i s a c o n v e n i e n t y a r d s t i c k

f o r t e s t i n g s i g n i f i c a n c e between t h e p e r c e n t of c r a s h e s f o r v a r i -

ous comparisons of r e a r l i g h t i n g sys tems p r e s e n t e d i n t h e fo l low-

i n g d i s c u s s i o n .

RESULTS.

I n t e r p r e t a t i o n Of A p p l i c a t i o n Of Methodology. F i g u r e s 5 .3

t h rough 5.12 compare t h e v a r i o u s r e a r l i g h t i n g sys tems . Two modes

a r e c o n s i d e r e d : t h e s t o p mode i n which a l e a d c a r sudden ly a p p l i e s

i t s b r a k e s and t h e t u r n - s t o p mode i n which t h e l e a d c a r i s s i g n a l -

i n g a t u r n and sudden ly b e g i n s an emergency s t o p . Each of t h e

f i g u r e s p r e s e n t s a cumula t ive p e r c e n t d i s t r i b u t i o n of c r a s h e s less

t h a n t h e v e l o c i t y i n d i c a t e d on t h e a b s c i s s a . For example, i n

F i g u r e 5 .3 t h e c u r v e f o r t h e p r e s e n t sys tem (System 1) i n d i c a t e s

t h a t app rox ima te ly 5 1 p e r c e n t of t h e c r a s h e s o c c u r r e d a t a v e l o c i t y

of z e r o f e e t p e r second o r less , t h u s i n d i c a t i n g no c r a s h . Simi-

l a r l y , app rox ima te ly 77 p e r c e n t o f t h e c r a s h e s o c c u r r e d a t 25 f e e t

p e r second o r less. T h i s i m p l i e s t h a t i n 26 p e r c e n t (77 minus 51)

of t h e c a s e s a c r a s h a t a v e l o c i t y between z e r o and twen ty - f ive

f e e t p e r second o c c u r r e d u s i n g System 1.

F i g u r e 5 . 3 r e p r e s e n t s t h e d r i v i n g s i t u a t i o n on t h e 1-71 e x p r e s s -

way n e a r Columbus, Ohio, d u r i n g a morning r u s h hour . V e l o c i t i e s and

headways were o b t a i n e d from t h e d a t a s u p p l i e d by Treiterer. Using

t h a t highway s i t u a t i o n , which i s c h a r a c t e r i z e d by uneven t r a f f i c

f l ow, lower t h a n normal expressway s p e e d , and s h o r t headways, w e

have super imposed emergency c a r - f o l l o w i n g s i t u a t i o n s . Under t h e s e

1 3 2

Relative Velocity A t Crash (FT/SEC)

Figure 5.3. Crash probability for system 1 and 8 in turn-stop mode on an expressway.

c o n d i t i o n s System 8 has fewer c r a s h e s a t a l l of t h e i n d i c a t e d

r e l a t i v e v e l o c i t i e s , i n c l u d i n g zero . For purposes of comparison

it can be seen t h a t System 1 had no c r a s h e s 51 p e r c e n t of t h e

time whi le System 8 had no c r a s h e s 6 2 p e r c e n t of t h e time, t h u s

i n d i c a t i n g a r e d u c t i o n i n c r a s h e s of 2 2 p e r c e n t (11 over 5 1 ) ,

g iven a d e f i n e d emergency. The magnitude of d i f f e r e n c e i s s i m i l a r

over a l l r e l a t i v e v e l o c i t i e s of c r a s h . Another measure of e f f e c -

t i v e n e s s i s t h e improvement i n t h e wors t c o n d i t i o n . I n t h e emer-

gency car - fo l lowing c o n f l i c t t h e wors t c o n d i t i o n would be a ve ry

h igh v e l o c i t y c r a s h . To compare t h e wors t c o n d i t i o n i n each s i t u a -

t i o n we have chosen t h e 99th p e r c e n t i l e of t h e cumulat ive r e l a -

t i v e v e l o c i t y a t c r a s h d i s t r i b u t i o n . Although t h i s measure i s

s u b j e c t t o random v a r i a b i l i t y it does provide an i n d i c a t i o n of

t h e wors t c a s e f o r v a r i o u s s i t u a t i o n s , A more meaningful compari-

son c a n , of c o u r s e , be made by comparing t h e e n t i r e d i s t r i b u t i o n .

For example, one might make such a comparison by over- laying t h e

graphs on a t r a n s p a r e n t s u r f a c e s o t h a t a l l cu rves p r o j e c t o n t o

one g r i d system.

F igure 5.4 r e p r e s e n t s t h e d r i v i n g s i t u a t i o n on a r u r a l two-

l a n e road under crowded c o n d i t i o n s . The v e l o c i t y d i s t r i b u t i o n s

used were o b t a i n e d from t h e Michigan S t a t e Highway Department

speed survey. The headways were ob ta ined from t h e Hyperlang head-

way model. This e v a l u a t i o n r e p r e s e n t s a volume l e v e l of 1050

v e h i c l e s pe r hour pe r l a n e . I n t h i s c a s e , System 1 has a zero

r e l a t i v e v e l o c i t y c r a s h l e v e l of 4 0 a s opposed t o a ze ro r e l a t i v e

v e l o c i t y c r a s h l e v e l of 50 f o r System 8 . This r e p r e s e n t s an improve-

ment of 25 p e r c e n t .

Appl ica t ion To Rear L igh t ing Systems Using Experimental ly

Measured Percep t ion Times: The E f f e c t Of Color Coding And Func-

t i o n a l Separa t ion . F igures 5 .3 through 5.6 and Table 5 .1 compare

l i g h t i n g Systems 1 and 8 i n t h e t u r n - s t o p mode a g a i n s t t h e base

Relative Velocity At Crash (FT/SEC)

Figu re 5 .4 . Crash p r o b a b i l i t y f o r system 1 and 8 i n t u rn - s t op mode on a two l a n e r u r a l highway.


F i g u r e 5 .5 . Crash p r o b a b i l i t y f o r system 1 and 8 i n t u r n s t o p mode on a n expressway assuming a n improved b r a k i n g system.


F igure 5 . 6 . Crash p r o b a b i l i t y f o r system 1 and 8 i n tu rn -s top mode on a two l ane r u r a l highway assuming an improved braking sy s tem .

TABLE 5.1. EFFECT OF COLOR CODING P?ITH FUNCTIONAL SEPARATION

V e a s u r e s o f E f f e c t i v e n e s s

F i g u r e Number

3

4

S t o p Lane P r e s e n t I 52 mph

5

s i g n a l s )

Turn- High 6 9 mph

84 mph Lane p r o v e -

p r o v e - ment

9 9 t h P e r c e n t i l e c r a s h v e l o c i t y

72 mph

46 mph

73 mph

Yode

Turn- S t o p

Turn- S t o p

Turn- S t o p

Turn-

Sys tem

1 ( 3 % m i s s e d s i g n a l s )

8

1 ( 3 % m i s s e d s i g n a l s )

8

I n t e n s i t y

, High

High

High

High

Highway Ty Pe

E x p r e s s - way

E x p r e s s - wav

Two- Lane

Two-

rake P e r c e n t o f c a s e s Type l w i t h no c r a s h e s

P r e s e n t

P r e s e n t

P r e s e n t

51%

6 2 %

4 0 %

c o n d i t i o n s of expressways ve r sus two-lane highways and t h e p r e s e n t

system versus a h y p o t h e t i c a l improved b rak ing system. A compari-

son of t h e percentage of no c r a s h e s i n d i c a t e d an improvement i n

magnitude of approximately 10 percentage p o i n t s , f o r t h e exper i -

mental r e a r l i g h t i n g system. Since t h e p r e s e n t system r e s u l t s i n

e i t h e r 40 o r 50 p e r c e n t no c r a s h e s (depending upon whether t h e

s imula t ion i s performed f o r a two-lane r u r a l highway o r a l i m i t e d

access expressway) an improvement of 20 o r 25 pe rcen t i s i n d i c a t e d

f o r t h e new r e a r l i g h t i n g system. This e v a l u a t i o n cons idered t h e

f a c t t h a t wi th t h e p r e s e n t system s i g n a l s were missed i n more than

three p e r c e n t of t h e exper imenta l obse rva t ions1 .

The d i f f e r e n c e s observed i n a comparison of t h e p r e s e n t and

an improved brake system a r e assumed t o be due t o random exper i -

mental e r r o r because t h e measured d i f f e r e n c e s between p e r c e n t of

c r a s h e s f o r p r e s e n t and improved b rak ing systems i s less than t h e

p rev ious ly e s t a b l i s h e d minimum s i g n i f i c a n t d i f f e r e n c e of t h r e e

pe rcen t . I t might be assumed t h a t brake system improvements would

i n c r e a s e t h e number of rear-end c rashes . The assumed 20 pe rcen t

improvement2 d i d n o t r e s u l t i n an i n c r e a s e i n c r a s h e s , b u t it d i d

cause a smal l i n c r e a s e i n h igher -ve loc i ty c r a s h e s , a s can be

observed by c a r e f u l s tudy of F igures 5.5 and 5.6. A comparison

of t h e base c o n d i t i o n s f o r t h e two-lane, r u r a l highway and t h e

expressway i n d i c a t e s t h a t t h e expressway cond i t ion has about 1 0

percentage p o i n t s fewer c r a s h e s when e i t h e r l i g h t i n g system o r

b rak ing system i s used. The r u r a l two-lane c o n d i t i o n repre -

sen ted a t r a f f i c volume of 1050 v e h i c l e s per hour pe r l a n e w h i l e

t h e expressway cond i t ion r e p r e s e n t e d a t r a f f i c volume of 1590

v e h i c l e s p e r hour pe r l a n e , Thus, i f t h e r e s u l t s were normalized

f o r t r a f f i c volume t h e d i f f e r e n c e s would probably be even l a r g e r .

A comparison of expressways and r u r a l , two-lane highways i n emer-

'A missed s i g n a l was expressed a s a f i v e second pe rcep t ion time i n s e r t e d i n t o t h e d i s t r i b u t i o n f o r t h r e e p e r c e n t of t h e p o s s i b l e pe rcep t ion t imes . Thus a missed s i g n a l was e q u a l l y l i k e l y f o r each e v e n t s imula ted .

2 ~ h e h y p o t h e t i c a l 2 0 p e r c e n t improvement was de f ined by s h i f t - i n g t h e a x i s of t h e cumulative b rake-dece le ra t ion d i s t r i b u t i o n t h a t was ob ta ined from T i g n o r ' s d a t a .

gency car-fol lowing s i t u a t i o n s would, of course , r e q u i r e normali-

z a t i o n of t r a f f i c f low, d r i v e r popu la t ion , and o t h e r important

f a c t o r s . However, t h i s s imula t ion technique provides a u s e f u l

t o o l f o r a comparison of road t y p e s , g iven t h e normal iza t ion of

base c o n d i t i o n s .

The E f f e c t Of I n t e n s i t y , Color Coding, And Funct ional Separa-

t i o n . - Figures 5.7 through 5.10 and Table 5.2 compare t h e e f f e c t of

changes i n l i g h t i n t e n s i t y and system c o n f i g u r a t i o n . F igures 5.7

and 5.8 compare t h e p r e s e n t r e a r l i g h t i n g c o n f i g u r a t i o n (System 1)

a t low i n t e n s i t y (35 c p , Experiment 1 . 1 . 2 ) w i th t h e improved con-

f i g u r a t i o n (System 8 ) a t low and high (91 cp , Experiment 1.1.1)

i n t e n s i t y i n t h e s t o p mode. With i n t e n s i t y f i x e d a t t h e lower l e v e l

t h e observed d i f f e r e n c e s between t h e c o n f i g u r a t i o n s a r e n e g l i g i b l e .

However, t h e r e i s a p o s i t i v e e f f e c t of inc reas ing t h e i n t e n s i t y i n

t h e s t o p mode f o r a l l l i g h t i n g system c o n f i g u r a t i o n s . This improve-

ment occurs over both highway cond i t ions .

I n c o n t r a s t , F igures 5.9 and 5.10 i n d i c a t e t h a t i n t h e t u r n -

s t o p mode i n t e n s i t y has ve ry l i t t l e e f f e c t whi le f u n c t i o n a l sepa-

r a t i o n of lamps and c o l o r coding a r e b e n e f i c i a l .

Thus, us ing t h e exper imenta l ly obta ined d a t a i n conjunct ion

wi th t h e s imula t ion model we can conclude t h a t s a f e t y i s improved

i n t h e s t o p mode by i n c r e a s i n g t h e l i g h t i n t e n s i t y , whi le l i g h t

i n t e n s i t y has very l i t t l e e f f e c t i n t h e tu rn - s top mode, Again

t h e e f f e c t o f expressways i s r e a d i l y apparen t .

The E f f e c t Of Funct ional S e p a r a t i o n , And Funct ional Separa-

t i o n With Color Coding. F igures 5.11 and 5.12 and Table 5.3 com-

p a r e t h e p r e s e n t r e a r l i g n t i n g system (System 1) wi th a system

having complete f u n c t i o n a l s e p a r a t i o n (System 4 ) and a system

having both complete f u n c t i o n a l s e p a r a t i o n and c o l o r coding

(System 8 ) . The e f f e c t of t h e s e coding techniques i s g r a p h i c a l l y

d e p i c t e d i n t h e f i g u r e s , which show t h a t each change c o n t r i b u t e d

an approximately equa l increment t o t h e t o t a l improvement.


Figure 5.7. Crash probability for system 8, high and low intensity signals, and system 1, low intensity, in the stop mode on an expressway.

Figure 5.8. Crash probability for system 8, high and low intensity signals, and system 1, low intensity, in the stop mode on a two lane rural highway.

Relat ive Velocity A t Crash (FT/SEC)

Figure 5.9. Crash probability for system 8, high and low intensity signals, and system 1, low intensity, in the turn-stop mode on an expressway.

Figure 5.10. Crash probability for system 8, high and low intensity signals, and system 1, low intensity, in the turn-stop mode on a two lane rural highway.

TABLE 5 .2 . EFFECT OF INTENSITY AND COLOR CODING WITH FUNCTIONAL SEPARATION

Yeasu res o f E f f e c t i v e n e s s

F i g u r e Number

7

8

9

Mode

10

S t o p

S t o p

S t o p

S t o p

S t o p

S t o p

Turn-

System

Turn- S t o p

Turn- S t o p

Turn- S t o p

Turn- S top

1

8

8

1

8

8

1 ( 3 %

I n t e n s i t y

S t o p / missed , s i q n a l s ) Turn- S t o p 8

8

1 ( 3 % mis sed s i g n a l s )

8

8

Low

Low

High

Low

Low

High

Low

Highway Type

Lob

High

Low

Low

High

Brake Type

Express- way Express- wa Y Expres s - way Two- Lane TWO - Lane Two- Lane

Expres s -

P r e s e n t

e r e s e n t

P r e s e n t

P r e s e n t

Expres s - way Two- Lane

Two- Lane

Two- Lane

P e r c e n t of c a s e s 1 9 9 t h P e r c e n t i l e w i t h no c r a s h e s ( c r a s h v e l o c i t y

1 I

4 6 mph

54 %

56%

5 9 %

42-4

43%

1 P r e s e n t

P r e s e n t

P r e s e n t

P r e s e n t

P r e s e n t

P r e s e n t

way

Express-

50 mph

51 mph

4 4 mph

57 mpn

56 mph

P r e s e n t

62%

4 2 %

48%

50%

4 7 % I 49 mph , I

54% 1 62 mph

way

45 mph

64 mPh

52 mph

51 mph

p r e s e n t 1

R e l a t i v e V e l o c i t y A t Crash

F i g u r e 5 .11. Crash p r o b a b i l i t y f o r systems 1, 4 and 8 , i n t h e t u r n - s t o p mode on an exp res s - way , t o show t h e e f f e c t of f u n c t i o n a l s e p a r a t i o n and c o l o r cod ing .

Relat ive Veloci ty A t Crash (FT/SEC)

Figure 5.12. Crash p r o b a b i l i t y f o r systems 1, 4 and 8 i n t h e tu rn-s top mode on a two l ane r u r a l highway, t o show t h e e f f e c t of f u n c t i o n a l s epa ra t i on and co lo r coding.

TABLE 5 .3 . EFFECT OF FUNCTIONAL SEPARATION AND FUNCTIONAL SEPARATION WITH COLOR CODING

Pleasures of E f f e c t i v e n e s s

Number

s i g n a l s )

12

Turn- S t o p

Turn- S top

Turn- S t o p

Turn- s t o p

4

8

I n t e n s i t y

High

4

8

High

Hiqh

9 9 t h p e r c e n t i l e c r a s h v e l o c i t y

6 6 mph

Brake Type

P r e s e n t

Highway Type

Express- way

Turn- / 1 (3% S t o p mis sed / s i g n a l s )

High

High

50 mph

P e r c e n t of c a s e s w i t h no c r a s h e s

5 2 %

Express- way Express- 45 mph

I way I

High Two- 1 ~ a n e

Two- Lane

Two- Lane

6 7 mph

P r e s e n t

67 mph

58%

6 2 % P r e s e n t

P r e s e n t

P r e s e n t

P r e s e n t 51 mph

41%

4 6%

5 0 %

CONCLUSIONS. An Evaluation of var ious r e a r l i g h t i n g con-

f i g u r a t i o n s was performed by comparing t h e c rash occurrence f o r

d i f f e r e n t conf igura t ions , which is determined using a Monte Carlo

s imulat ion of emergency d r iv ing c o n f l i c t s . The following conclu-

s ions r e s u l t from t h i s ana lys i s :

1. The conf igura t ion f e a t u r i n g co lo r coding and geometric

separa t ion (System 8 ) can reduce rear-end c ra sh occurrence 2 0 t o

25 percent compared t o t he p re sen t r e a r l i g h t i n g conf igura t ion

given t h e emergency c o n f l i c t i n which a d r i v e r who i s s igna l ing

f o r a t u r n on a high-volume highway suddenly makes an emergency

s top .

2 . Geometric s epa ra t ion and c o l o r coding each con t r ibu te

s i g n i f i c a n t l y t o t h e repor ted c rash reduct ions .

3 . For a cons tan t presence/s ignal i n t e n s i t y r a t i o an

increase i n i n t e n s i t y of r e a r s igna l ing lamps approximately

from SAE c l a s s B t o c l a s s A minimum i n t e n s i t i e s can reduce r ea r -

end c ra sh occurrence about 1 0 percen t , given t h e emergency con-

f l i c t i n which a d r i v e r t r a v e l i n g on a high volume highway sud-

denly makes an emergency s top .

4 . The improvements repor ted above occurred aga ins t base

condi t ions cons i s t i ng of combinations of expressway versus two-

l ane highway and p re sen t versus a hypo the t i ca l ly improved braking

system.

5 . A u se fu l methodology f o r eva lua t ing t h e e f f e c t of com-

ponent improvements on c rash reduc t ion has been developed.

6. HEADWAY CHANGE DETECTION AS A FUNCTION OF PRESENCE LIGHT ARRAY (TASK 6 )

I n o r d e r t o improve a d r i v e r ' s pe rcep t ion of t h e change i n

d i s t a n c e between h i s c a r and t h e one he i s fo l lowing , va r ious

forms of presence l i g h t d i s p l a y s were eva lua ted . The presence

l i g h t d i s p l a y g e n e r a l l y used c o n s i s t s of two lamps, p laced c l o s e

t o t h e edge of t h e v e h i c l e , which vary i n shape and s i z e , Most

v e h i c l e s have, on e i t h e r s i d e , two lamps of a t l e a s t 3.5 square

inches . Other v e h i c l e s have lamps wi th m u l t i p l e compartments i n

which t h e luminous a r e a of t h e lamps i s g e n e r a l l y l a r g e r than

t h e minimum Class-B requirement . I n some cases t h e presence

l i g h t i s a luminous s t r i p running t h e f u l l width of t h e v e h i c l e ,

The p r i n c i p a l cue used by d r i v e r s t o determine headway

change with a l e a d v e h i c l e i s t h e v i s u a l angle subtended by t h e

edges of t h e v e h i c l e , which a t n i g h t would be d e l i n e a t e d by t h e

o u t s i d e edge of t h e presence l i g h t s . Headway change i s d e t e c t e d

p r i n c i p a l l y on t h e b a s i s of a change i n t h i s ang le , and secon-

d a r i l y by t h e changes i n a r e a and b r i g h t n e s s which occur a s a

func t ion of t h e v i s i b i l i t y d i s t a n c e (Parker e t a l , , 1964) . The

e f f e c t upon b r i g h t n e s s of lamp a r e a and i n t e n s i t y i s dependent

upon t h e viewing d i s t a n c e , and t h e r e l a t i o n s h i p i s n o t c l e a r l y

understood (Merik, 1968; P r o j e c t o r e t a l . , 1969) .

Based upon t h e assumption t h a t t h e v i s u a l ang le i s t h e

p r i n c i p a l cue f o r c l o s u r e d e t e c t i o n , it was considered p o s s i b l e

t h a t some lamp a r r a y s would provide l a r g e r ang le s than o t h e r s .

For example, wi th a given v e h i c l e s i z e and lamp spac ing , a two-

lamp a r r a y i n which one lamp i s p laced a t each edge of t h e v e h i c l e

c r e a t e s a f i x e d v i s u a l angle f o r a given viewing d i s t a n c e . I t i s

p o s s i b l e t o i n c r e a s e t h i s v i s u a l ang le by t h e use of f o u r lamps

i n which a p a i r of lamps a r e mounted one above t h e o t h e r on t h e

v e h i c l e s t r u c t u r e . This would then provide t h e observer wi th a

s o l i d v i s u a l angle which had both a v e r t i c a l and a h o r i z o n t a l

angu la r component. I t was hypothesized t h a t t h i s se t -up might

provide d r i v e r s wi th a d d i t i o n a l cues and, hence, i nc r ea se t h e i r

s e n s i t i v i t y t o changes i n headway.

SIMULATION STUDIES. A s one means of a t t a c k i n g t h i s problem

a l abo ra to ry s imula t ion was devised t o vary t h e presence l i g h t

d i s p l a y e a s i l y i n terms of t h e con f igu ra t i on of lamps a s a f f e c t e d

by t h e i r number, t h e i r r e l a t i v e l o c a t i o n h o r i z o n t a l l y and v e r t i -

c a l l y , and t h e spacing between them. I n a d d i t i o n , i n t e n s i t y and

c o l o r changes could be r e a d i l y made.

The s imu la to r cons i s t ed of a f l a t s u r f a c e 20 f e e t long; on

t o p of t h i s was a c a r r i a g e which he ld t h e l i g h t i n g assembly. The

c a r r i a g e was t i e d t o a continuous loop of wire which was wound

around a crank. I n t h i s way, t h e c a r r i a g e moved i n t h e d i r e c t i o n

i n which t h e crank was tu rned . The s u r f a c e on which t h e c a r r i a g e

t r a v e l e d and t h e c a r r i a g e i t s e l f a r e shown i n Figure 6 . 1 . Three

h o r i z o n t a l cu t -ou t s were made i n t h e f r o n t of t h e c a r r i a g e d i sp l ay

i n such a manner t h a t masks wi th accu ra t e a p e r t u r e s i n them could

be s l i d i n t o each cu t -ou t , The a p e r t u r e s i n t h e masks s imula ted

t h e a r e a s and shapes of t h e presence lamps. I n a d d i t i o n , co lo red

f i l t e r s could be i n s e r t e d behind t h e masks s o t h a t va r i ous c o l o r s

could be examined.

The t e s t s u b j e c t was s e a t e d i n a c h a i r and viewed t h e d i s p l a y

through an a p e r t u r e which was s l i g h t l y h igher than t h e d i s p l a y

t a b l e su r f ace . On t h e o t h e r s i d e of t h e viewing a p e r t u r e was

p laced a l i g h t box con ta in ing s i x tungs ten f i l amen t lamps which

had a r a t i n g of 15 w a t t s and opera ted a t up t o 110 v o l t s . A d i f -

f u s ion sc reen was p laced a t t h e lower edge of t h e box t o provide

a uniform l i g h t source . A t an ang le of 45 degrees from t h e l i g h t

box t h e r e was a p i ece of 1/8-inch t h i c k g l a s s through which t h e

s u b j e c t viewed t h e c a r r i a g e d i sp l ay . A t t h e same time t h e s u b j e c t

viewed t h e r e f l e c t i o n of t h e luminous a r e a produced by t h e l i g h t

box. Therefore , t h e s u b j e c t was, i n e f f e c t , viewing t h e c a r r i a g e

d i s p l a y through an a r e a of uniform luminance. The i n t e n s i t y of

t h i s luminous a r e a was ad ju s t ed u n t i l it was equ iva l en t t o a r e a l

F i g u r e 6 . 1 . C a r r i a g e l i g h t i n g a r r a y and t a b l e and t h e s u b j e c t ' s s t a t i o n .

n i g h t - d r i v i n g cond i t ion . I n s t u d i e s 1 - 5 t h i s luminance was

0.08 f t / l and i n experiment 6 it was 2 . 4 f t / l . I t has been

r e p o r t e d (Schmidt, 1961) t h a t n i g h t d r i v i n g i s done w i t h i n a

range of ,003 t o 4.0 f t / l .

S i m i l a r l y , t h e luminous i n t e n s i t y of t h e l i g h t s t h a t were

p resen ted by means of t h e c a r r i a g e d i s p l a y , f o r each of t h e c o l o r s

used, were c a l i b r a t e d .

The a p e r t u r e through which t h e observer viewed t h e presence

l i g h t d i s p l a y s i s shown i n Figure 6.2. Monocular viewing was used

t o remove t h e e f f e c t s of b inocu la r cues t h a t would a f f e c t t h e simu-

l a t i o n b u t which a r e n o t important f o r d i s t a n c e judgment a t t h e

s imula ted r e a l d i s t a n c e s i n d r i v i n g .

I n o r d e r t o provide a s u b s i d i a r y loading t a s k , t h r e e amber

and t h r e e green l i g h t s were f i x e d t o a v e r t i c a l f l a t s u r f a c e a t

t h e f r o n t edge of t h e t a b l e on which t h e c a r r i a g e rode. These

lamps were energized a t an average frequency of one every t e n

seconds and remained l i g h t e d f o r a pe r iod of f o u r seconds. The

obse rve r h e l d a swi tch box con ta in ing two swi tches , one f o r opera-

t i o n by t h e r i g h t and t h e o t h e r f o r opera t ion by t h e l e f t thumb.

The r i g h t swi tch was t o be depressed whenever an amber l i g h t

appeared and t h e l e f t whenever a green l i g h t appeared on t h e pane l ,

A s soon a s t h e observer responded t h e l i g h t was ext inguished.

This arrangement i s shown i n Figure 6.3.

S i x s e p a r a t e s t u d i e s which were conducted us ing t h e simula-

t i o n f a c i l i t y a r e desc r ibed below.

Study 1. S i x presence l i g h t a r r a y s were s imula ted . I n t h i s

tes t t h e s u b s i d i a r y t a s k was n o t used. The presence l i g h t a r r a y s

t h a t were eva lua ted a r e shown i n Figure 6.4.

Procedure. The i n i t i a l d i s t a n c e between t h e s u b j e c t ' s

eye p o i n t and t h e p o s i t i o n of t h e d i s p l a y c a r r i a g e was 20 f e e t ,

The s u b j e c t was i n s t r u c t e d t o respond by saying "now" whenever he

could d e t e c t t h a t t h e d i s p l a y had been c l e a r l y moved towards him.

The d i s t a n c e by which t h e d i s p l a y c a r r i a g e was moved be fo re t h e

s u b j e c t had responded was recorded t o t h e n e a r e s t 0.5 inch. A t

F i g u r e 6 . 2 . Monocular a p e r t u r e f o r viewing t h e l i g h t i n g a r r a y , and t h e s u b s i d i a r y t a s k l i g h t s r e s p o n s e s w i t c h box.

Figure 6.3. The location of the subsidiary task lamps, one of which is lighted.

0 .5 i n . 0 .5 i n .

0 0 . 5 i n . 2

4-6 i n . -b

5 * 6 i n .

6 * 6 i n .

0 0 . 5 i n . 2

0.5 i n .

0 0 . 5 i n . 2

0 0 . 5 i n . 2

0 0 . 5 i n . 2

F i g u r e 6 . 4 . Red, p r e s e n c e l i g h t a r r a y s u s e d i n study 1.

t h e conc lus ion of t h e test each saub jec t rank-ordered t h e a r r a y s

f o r e f f e c t i v e n e s s i n g i v i n g headway change in fo rmat ion .

R e s u l t s . The geometr ic mean d i sp lacements , when t h e

s u b j e c t had responded f o r each of t h e l i g h t i n g a r r a y s , a r e shown

i n Table 6.1. An a n a l y s i s of v a r i a n c e was run on t h e response

d a t a and it was found t h a t d i f f e r e n c e s between a r r a y s d i d e x i s t .

This a n a l y s i s i s shown i n Table 6.2, A Newman-Keuls test subse-

q u e n t l y c a r r i e d o u t a c r o s s a r r a y s showed t h a t a r r a y 1 was s i g n i f i -

c a n t l y poore r than a l l o t h e r s ( i . e . , had a s i g n i f i c a n t l y l a r g e r

mean displacement a t t h r e s h o l d ) and t h a t a r r a y 2 was s i g n i f i c a n t l y

poore r than a r r a y 6. Other comparisons were n o t s i g n i f i c a n t . The

mean rank ings showed t h a t s u b j e c t s p r e f e r r e d multi-lamp a r r a y s par-

t i c u l a r l y t h o s e having a v e r t i c a l component.

Study 2. I n o r d e r t o determine t h e i n f l u e n c e of lamp lumi-

nance and candlepower t h r e e a r r a y s were examined (F igure 6 . 5 ) , one

of which c o n s i s t e d of a cont inuous band of l i g h t , 6.0 x 0.5 i n c h e s ,

a c r o s s t h e width of t h e d i s p l a y and which was run a t an average

luminance of 7 .5 f t / l . A second d i s p l a y , which a l s o c o n s i s t e d of

a cont inuous b a r of l i g h t a c r o s s i t s wid th , was opera ted a t a

luminance of 1.25 f t / l . A t h i r d a r r a y c o n s i s t e d of two lamps

1 / 2 inch square opera ted a t a luminance of 7.5 f t / l . These a r r a y s

were used t o g i v e e q u a l luminance v a l u e s f o r a r r a y s 1 and 3 and

e q u a l candlepower va lues f o r a r r a y s 2 and 3 , Using t h i s a r range-

ment, t h e e f f e c t s of d i f f e r e n t i a l candlepower produced by a r r a y s

opera ted a t t h e same luminance b u t d i f f e r i n g i n a r e a could be

compared. Examination of a r r a y s 1 and 2 shows t h e e f f e c t of e q u a l

lamp a r e a and d i f f e r e n t luminance and candlepower.

I n t h i s t e s t t h e s u b s i d i a r y t a s k l i g h t s were employed, and

s u b j e c t s responded t o them a s r a p i d l y a s p o s s i b l e a s desc r ibed

above. Twelve s u b j e c t s wi th normal c o l o r v i s i o n were used.

R e s u l t s . The geometr ic mean d isplacement a t t h r e s h o l d

was computed f o r each of t h e t h r e e a r r a y s . An a n a l y s i s of v a r i a n c e

was c a r r i e d o u t on t h e d isplacement t h r e s h o l d s , and it was found

TABLE 6.1, STUDY 1: GEOMETRIC MEAN DISPLACEMENT FOR EACH ARRAY. DATA FOR 12 SUBJECTS

Array Mean Displacement (Inches)

* Mean Rank

* Effectiveness Rating 1 (LOW) - 6 (High)

TABLE 6.2 STUDY 1: ANALYSIS OF VARIANCE OF DISPLACEMENT VALUES.

Source SS df MS F

BETWEEN SUBJECTS 47.29 11

WITHIN SUBJECTS

Arrays

Arrays x Subjects

Within Cells

* Significant at P > - - 0.01

Array

0.5 in.

.t----- 6 in. -

7.5 FT/L

0 0 . 5 in. 2

Figure 6 . 5 Red, presence light arrays used in study 2 .

t h a t t h e r e were no s i g n i f i c a n t d i f f e r e n c e s between a r r a y s . Table

6.3 shows t h e geometric mean displacement f o r each a r r a y and t h e

mean rank.

Study 3. I n another experiment s i x presence l i g h t a r r a y s

were eva lua ted us ing t he s imula t ion . The purpose of t h i s s tudy was

t o ob t a in some f u r t h e r d a t a f o r comparison of h o r i z o n t a l and v e r t i -

c a l a r r ays composed of l i g h t s 1/2 inch square mounted a t t h e edge

of t h e c a r r i a g e d i s p l a y . Hor izonta l arrangements were compared

with v e r t i c a l arrangements of t h e same lamp spacing; four lamp

a r r a y s arranged i n t he form of a square o r r e c t ang l e were a l s o

compared. A l l t h e lamps were red and were opera ted a t a luminance

of 7.5 f t / l . Twenty-five s u b j e c t s with normal co lo r v i s i o n were

used, and a r r ays were presented i n a random order f o r t e n t r i a l s

i n each a r r ay .

The a r r ays were s e l e c t e d i n o rder t o f a c i l i t a t e a comparison

between h o r i z o n t a l and v e r t i c a l a r r a y s i n which lamp sepa ra t i on

d i s t a n c e was t h e same. Two lamp sepa ra t i on d i s t a n c e s were used

f o r both h o r i z o n t a l and v e r t i c a l d i sp l ays . I n a d d i t i o n , a com-

bined h o r i z o n t a l and v e r t i c a l d i sp l ay c o n s i s t i n g of four lamps

was used i n two con f igu ra t i ons which d i f f e r e d i n t he v e r t i c a l

s epa r a t i on d i s t a n c e . These a r r a y s a r e shown i n Figure 6 . 6 ,

Resu l t s . The geometric mean displacement f o r each of

t he a r r a y s , shown i n Table 6 . 4 , i n d i c a t e s t h a t h o r i z o n t a l d i s -

p lays have s l i g h t l y lower displacement t h r e sho ld s than equiva-

l e n t v e r t i c a l d i s p l a y s i n which lamp sepa ra t i on was t h e same.

This can be seen by comparing t h e r e s u l t s f o r a r r a y s 1 and 2 with

t h e corresponding v e r t i c a l a r r a y s 3 and 4. The four lamp a r r a y s

provided somewhat lower displacements than two lamp a r r ays . An

a n a l y s i s of va r iance of t h e s e d a t a showed t h a t t h e r e were s i g n i f i -

c a n t d i f f e r e n c e s between a r r a y s . The r e s u l t s of a Newman-Keuls

tes t showed t h a t a r r a y s 6 , 5 , and 2 provided s i g n i f i c a n t l y s h o r t e r

displacement th resho lds ( i . e . , s u p e r i o r performance) than a r r a y s

3 , 1, and 4 . The mean ranking of each a r r a y showed t h a t s u b j e c t s

Array

, 5 i n . 2

, 5 i n . 2

.5 i n . 2

3.55 i n .

-6 i n . ------.t

t .5 i n . 2

5 m 3.25 i n .

.5 i n . 2

F i g u r e 6 .6 . Red, p r e s e n c e l i g h t a r r a y s used i n s t u d y 3 t o show t h e e f f e c t o f h o r i z o n t a l , v e r t i c a l , and combined h o r i z o n t a l / v e r t i c a l d i s p l a y s . 161

TABLE 6.3. STUDY 2: GEOMETRIC MEAN DISPLACEMENT FOR THREE ARRAYS. DATA FOR 1 2 SUBJECTS

Array Mean Displacement (inches) Mean Rank

TABLE 6.4. GEOMETRIC MEAN DISPLACEMENT FOR EACH ARRAY USED IN STUDY 3. DATA FOR 25 SUBJECTS.

Array Mean Displacement Mean Rank (inches)

1 32.5 3 .48

2 26 .8 4.14

3 3 3 . 1 2 . 4 8

4 32.0 2 . 7 1

5 23.7 3 .90

6 25 .3 4.29

Array

0 . 5 in.

.5 i n .

1 . 0 in.

1.5 in.

0 2.0 in.

2.5 in.

Lighted/Total

Area

I/ 6

Figure 6 . 7 Red, presence l i g h t a r r ays used t o evaluate t h e e f f e c t of t h e r a t i o of l i $ h t e d / t o t a l area between lamps i n study 4 .

judged s m a l l lamp s e p a r a t i o n poore r t h a n l a r g e s e p a r a t i o n , ve r -

t i c a l a r r a y s poore r t h a n h o r i z o n t a l , and e i t h e r v e r t i c a l o r

h o r i z o n t a l s e p a r a t i o n a l o n e a s poorer t han combined h o r i z o n t a l /

v e r t i c a l a r r a y s .

Study 4 . I n t h i s exper iment , a t o t a l of twelve s u b j e c t s

w i t h normal c o l o r v i s i o n were used t o de te rmine t h e e f f e c t of

t h e r a t i o of t h e l i g h t e d a r e a t o t h e a r e a between t h e l i g h t s

upon d isp lacement t h r e s h o l d s . The s i x d i s p l a y arrangements used

a r e shown i n F igu re 6 .7 . I t should be no ted t h a t t h e r a t i o s of

t h e l i g h t e d a r e a compared t o t h e t o t a l a r e a a v a i l a b l e f o r t h e

l i g h t , a s measured by t h e d i s t a n c e between t h e extreme o u t s i d e

edges of t h e lamps, have v a l u e s of 1:6 f o r t h e two lamp condi-

t i o n t o 1:1, which r e p r e s e n t s a b a r of l i g h t a c r o s s t h e f u l l

wid th of t h e d i s p l a y . A l l a r r a y s were r e d a t 7.5 f t / l ,

Each a r r a y was p r e s e n t e d t o t h e s u b j e c t s i n a random o r d e r

and t e n t r i a l s were c a r r i e d o u t w i t h each a r r a y ,

R e s u l t s . The geomet r ic mean d isp lacement v a l u e s i n

i nches f o r each of t h e s i x a r r a y s a r e shown i n Table 6 .5 , These

d a t a show t h a t a s t h e l i g h t e d a r e a i n c r e a s e s t h e r e i s i n a lmos t

a l l c a s e s a dec rease i n t h e d i sp lacement t h r e s h o l d . An a n a l y s i s

of v a r i a n c e d i d n o t f i n d a s i g n i f i c a n t a r r a y e f f e c t , S u b j e c t s

ranked h i g h e s t t h o s e a r r a y s t h a t were i n t e r m e d i a t e i n l i g h t e d / t o t a l

a r e a .

Study 5. I n o r d e r t o check t h e r e s u l t s of some of t h e d a t a

found i n Study 1, s p e c i f i c a l l y t h e comparison between a two lamp

and a f o u r lamp a r r a y i n c o r p o r a t i n g h o r i z o n t a l and v e r t i c a l com-

ponen t s , a f i f t h s tudy l i m i t e d t o t h r e e a r r a y s was conducted.

S e l e c t e d f o r o b s e r v a t i o n were a s i n g l e lamp a r r a y , such a s found

on motorcyc les and expec ted t o p rov ide t h e l e a s t p r e c i s i o n f o r

d e t e c t i o n of d i sp lacement change, a two lamp h o r i z o n t a l a r r a y ,

and a f o u r lamp a r r a y i n which two h o r i z o n t a l lamps were v e r t i -

c a l l y spaced from ano the r p a i r of h o r i z o n t a l l y spaced lamps. The

a r r a y s a r e shown i n F igu re 6.8. I n t h i s t e s t t h e twelve s u b j e c t s

Array

0 .5 in. 2

6 in.

0.5 in. 2

0.5 in. 2

Figu re 6 .8 . Red, presence l i g h t a r r a y s used i n s tudy 5 t o f u r t h e r e v a l u a t e h o r i z o n t a l and combined h o r i z o n t a l / v e r t i c a l d i s p l a y s .

used observed s i x t e e n t r i a l s wi th each of t h e t h r e e a r r a y s . Each

a r r a y was p resen ted i n a random o r d e r f o r e i g h t t r i a l s wi th each

a r r a y , fol lowed by a second randomizat ion of t h e t h r e e a r r a y s wi th

t h e remaining e i g h t t r i a l s p e r a r r a y . A l l a r r a y s were r e d a t 7.5

Resu l t s . The geometric mean d isplacement va lues and t h e

mean ranks ob ta ined wi th each of t h e a r r a y s a r e shown i n Table 6.6.

The s t a t i s t i c a l a n a l y s i s showed t h a t , a s expected , t h e s i n g l e lamp

a r r a y had a s i g n i f i c a n t l y l a r g e r t h r e s h o l d d isplacement than a r r a y s

2 and 3. The d i f f e r e n c e between a r r a y s 2 and 3 was s m a l l , a l though

a r r a y 3 d i d provide a s i g n i f i c a n t l y more s e n s i t i v e d i s p l a y t o t h e

s u b j e c t s than t h e two lamp a r r a y . Array 1 was c l e a r l y ranked poor-

e s t , b u t a r r a y 3 was ranked n o t much lower than 2 .

Studv 6 . A f i n a l tes t was c a r r i e d o u t t o determine t h e e f f e c t

of green-blue and r e d d i s p l a y l i g h t s when each were used wi th f o u r

d i s p l a y c o n f i g u r a t i o n s . The c o n f i g u r a t i o n s v a r i e d t h e number

of lamps used. Conf igura t ion 1 c o n s i s t e d of a s i n g l e lamp a r r a y ;

c o n f i g u r a t i o n 2 c o n s i s t e d of two lamps h o r i z o n t a l l y spaced; con-

f i g u r a t i o n 3 c o n s i s t e d of two lamps h o r i z o n t a l l y spaced w i t h an

a d d i t i o n a l lamp spaced v e r t i c a l l y between t h e two h o r i z o n t a l

lamps t o form a t r i a n g u l a r d i s p l a y ; c o n f i g u r a t i o n 4 c o n s i s t e d of

f o u r lamps. These a r r a y s a r e shown i n F igure 6.9.

I n t h i s t e s t t h e procedure was modif ied. T r i a l s were run

w i t h t h e c a r r i a g e moved e i t h e r toward t h e obse rve r o r away from

him. The s u b j e c t s i g n a l l e d a s soon a s he c l e a r l y saw a d i s p l a c e -

ment, and he i n d i c a t e d whether t h e d isplacement was towards him

o r away from him. The i n t e n s i t y of t h e d i s p l a y l i g h t s was r a i s e d

t o 50 f t / l , and t h e i n t e n s i t y of t h e a d a p t a t i o n f i e l d was i n c r e a s e d

t o 2 . 4 f t / l . The a d a p t a t i o n luminance was s t i l l w i t h i n t h e range

t h a t would be found i n a c t u a l n i g h t d r i v i n g , and t h e i n t e n s i t y

v a l u e s of t h e d i s p l a y l i g h t s were c l o s e r t o a c t u a l va lues found on

v e h i c l e presence lamps.

S u b j e c t s r ece ived a t o t a l of 3 2 t r i a l s f o r each of t h e two

TABLE 6 . 5 . STUDY 4 : GEOMETRIC MEAN DISPLACEMENT FOR ARRAYS D I F F E R I N G I N LIGHTED AREA/TOTAL AREA. DATA FOR 1 2 SUBJECTS

A r r a y M e a n D i s p l a c e m e n t Mean R a n k ( i n c h e s )

1 3 6 . 5 2 . 2 5

TABLE 6 . 6 . GEOMETRIC MEAN DISPLACEMENTS FOR EACH OF THREE ARRAYS USED I N STUDY 5

A r r a y M e a n D i s p l a c e m e n t Mean R a n k ( i n c h e s )

Array

6 i n .

I a

6 in.

0.5 i n . 2

0.5 i n . 2

0 .5 i n . 2

0 . 5 i n . 2

Figure 6 . 9 . Red and green-blue presence l i g h t a r r a y s used i n s tudy 6 .

colored d i sp lays . There were e i g h t t r i a l s f o r each d isplay-color

combination, I n f o u r of t h e s e t h e d i s p l a y approached t h e s u b j e c t

and i n t h e o t h e r f o u r it receded, Within a p a r t i c u l a r colored

a r r a y t h e o rde r ing of approaching and receding t r i a l s was random-

i zed . I n each case t h e i n i t i a l d i s t a n c e of t h e d i s p l a y from t h e

observer was 2 0 f e e t . A f u l l s e t of t r i a l s were run f i r s t wi th

one c o l o r i n each of t h e a r r a y combinations and then wi th t h e

o t h e r co lo r . The o rde r ing of c o l o r s was a l t e r n a t e d ac ross s u b j e c t s .

A t t h e conclusion of t h e test t h e a r r a y s were rank ordered ,

Resu l t s , A a n a l y s i s of var iance was c a r r i e d o u t on t h e

displacement t h r e s h o l d s , I t was found t h a t s i g n i f i c a n t e f f e c t s

were caused by t h e a r r a y s and the a r r a y x d i r e c t i o n of motion

i n t e r a c t i o n , The r e s u l t s of a Newman-Keuls t e s t c a r r i e d ou t on

t h e a r r a y x d i r e c t i o n i n t e r a c t i o n showed t h a t when t h e d i s p l a y

was moved away from t h e observer a r r a y 4 , t h e four lamp a r r a y ,

had s i g n i f i c a n t l y lower displacement th resho lds than t h e o t h e r

t h r e e a r r a y s . When t h e d i s p l a y was moved toward t h e observer

it was found t h a t t h e s i n g l e lamp a r r a y was s i g n i f i c a n t l y poorer

than a l l o t h e r s . Array 4 was s i g n i f i c a n t l y b e t t e r , having lower

displacement va lues , than a r r a y s 2 o r 3 , There were no s i g n i f i -

c a n t d i f f e r e n c e s between a r r a y 3 and 2.

I n a d d i t i o n , t h e a n a l y s i s of var iance showed t h a t t h e r e were

no d i f f e r e n c e s due t o t h e co lo r s .

Table 6 . 7 shows t h e median displacement th resho lds f o r red

and green-blue a r r a y s i n t h e approaching and t h e receding condi-

t i o n s . I t w i l l be noted t h a t i n t h e receding condi t ion t h e

th resho ld va lues a r e h igher than i n t h e approach cond i t ion except

f o r a r r a y 1. The s u p e r i o r i t y of t h e four lamp a r r a y can a l s o be

seen.

The mean rankings of t h e a r r a y s i n each c o l o r a r e shown i n

Table 6 . 8 . I t w i l l be noted t h a t a r r a y s 3 and 4 were ranked equa l

by t h e s u b j e c t s f o r t h e red l i g h t s followed by a r r a y 4 and 3 i n

green-blue, t h e two lamp a r r a y s i n r ed and green, with t h e s i n g l e

lamp a r r a y s ranked lowest , Thus, t h e s u b j e c t i v e e v a l u a t i o n s of

169

TABLE 6.7. STUDY 6: MEDIAN DISPLACEMENTS FOR RED AND GREEN-BLUE DISPLAYS FOR APPROACHING AND RECEDING TRIALS. DATA FOR 18 SUB- JECTS, ALL COLOR NORMAL

Array Median Displacement (inches)

Approaching I Receding

TABLE 6.8. STUDY 6: MEAN RANKING OF EACH ARRAY IN EACH COLOR FOR 18 SUBJECTS

Red Green-Blue

1 50.0 45.0

2 31.5 29.5

3 28.0 30.5

Array Color

Red Green-Blue

41.5 43.0

37.5 37.5

35.5 35.5

Red - Green-Blue

1 1.44 1.56

2 4.17 3.67

3 6.61 6.06

4 6.33 6.17

a r r a y e f f e c t i v e n e s s c l o s e l y p a r a l l e l e d t h e o b j e c t i v e performance

d a t a except f o r a r r a y 3 i n r ed wi th which s u b j e c t s performed

poorer than a r r a y 4 i n e i t h e r c o l o r ,

HEADWAY CHANGE DETECTION AS A FUNCTION OF PRESENCE LIGHT

ARRAY I N A CAR-FOLLOWING TASK, The s imula t ion s t u d i e s , were con-

cerned wi th t h e e f f e c t of va r ious arrangements of presence lamp

a r r a y s upon t h e displacement t h r e s h o l d s observed by s u b j e c t s

w i t h i n t h e t e s t s i t u a t i o n . The s t u d i e s found t h a t an a r r a y which

incorpora ted a v e r t i c a l component i n a d d i t i o n t o t h e usua l h o r i -

z o n t a l component inc reased a s u b j e c t ' s a b i l i t y t o d e t e c t change

i n headway, i . e . , less change was necessary be fo re t h e s u b j e c t

n o t i c e d a change. The lamp a r r a y which was found most e f f e c t i v e

i n reducing displacement t h r e s h o l d s was one i n which two lamps

were mounted above a two lamp h o r i z o n t a l a r r a y . A t r i a n g u l a r

t h r e e lamp a r r a y was l e s s e f f e c t i v e ,

I t seemed d e s i r a b l e t h a t t h e s imula t ion be v a l i d a t e d i n a

s tudy us ing a c t u a l v e h i c l e s d r iven on a highway. Two i n s t r u -

mented v e h i c l e s were prepared. They could be run a t p re - se t

speeds , by means of speed-con t ro l s , and a s p e c i f i c headway could

be e s t a b l i s h e d between them and subsequently maintained. I n

a d d i t i o n , it was r e q u i r e d t h a t a f t e r t h e v e h i c l e s had been run-

n ing a t t h e e s t a b l i s h e d headway f o r some pe r iod of t ime t h e l e a d

v e h i c l e would begin t o c o a s t . The change i n headway which would

occur be fo re s u b j e c t s d e t e c t e d t h a t t h e v e h i c l e had s t a r t e d t o

c o a s t would then be measured, This measurement of change i n head-

way a t d e t e c t i o n was i d e n t i c a l t o t h e one t h a t had been used i n

t h e s imula t ion s t u d i e s . c o a s t i n g d e c e l e r a t i o n s were used t o

o b t a i n a moderate r e l a t i v e v e l o c i t y between t h e two v e h i c l e s .

Test Vehic les . A block diagram of t h e ins t rumenta t ion i n

both t h e l e a d and t h e fo l lowing v e h i c l e used i n t h e s e tests i s

shown i n Figure 6 . 1 0 . The l e a d v e h i c l e c a r r i e d an a r r a y of e i a h t

lamps mounted a s shown i n Figure 6 . 1 1 , Each lamp opera ted inde-

pendent ly t o provide a v a r i e t y of r e a r l i g h t i n g d i s p l a y s . A

Figure 6.10. Closure detection vehicle instrumentation.

------

Mounted Task Lamps

Start Calibration and Control

Set I 0 0 O o O I Vehicle Rear Lamps I

I Lead CarlFollowing Car -- --

Figure 6.11. Test ca r s showing layout of lamps on lead car .

master c o n t r o l switched a l l lamps s e l e c t e d on and o f f s imul tan-

eous ly . The l i g h t o u t p u t from each lamp was c o n t r o l l e d inde-

pendent ly by a s o l i d s t a t e v o l t a g e r e g u l a t o r and a v o l t a g e a d j u s t

po ten t iomete r ,

Both v e h i c l e s were f i t t e d wi th an FM communications t r a n s -

c e i v e r , an au tomat ic speed c o n t r o l wi th speed p r e - s e t mode, and

a f i f th -whee l d i s t a n c e t r ansduce r wi th an ou tpu t of one pu l se p e r

f o o t . The responses of t h e d r i v e r and passenger i n t h e fo l lowing

c a r , which occurred when they d e t e c t e d t h a t t h e l e a d v e h i c l e was

c o a s t i n g and t h a t t h e d i s t a n c e between t h e i r v e h i c l e and t h e l e a d

v e h i c l e had decreased , were t r a n s m i t t e d wi th f i f th -whee l p u l s e s

from t h e fo l lowing c a r t o t h e l e a d c a r through a t e l e m e t r y l i n k .

Data read-out in s t rumen ta t ion i n t h e l e a d c a r c o n s i s t e d of

a d i g i t a l t imer wi th 0 . 0 1 seconds r e s o l u t i o n and a d i g i t a l up-

down coun te r which provided a headway change d i s p l a y t o a reso-

l u t i o n of one f o o t f o r each s u b j e c t . A t h i r d up-down counter pro-

v ided t h e l e a d c a r d r i v e r wi th a cont inuous d i g i t a l d i s p l a y of

t h e headway between t h e two v e h i c l e s , The f i f th -whee l d i s t a n c e

p u l s e s f o r both c a r s were cont inuous ly a p p l i e d t o a p p r o p r i a t e

i n p u t s t o t h e t h r e e up-down coun te r s .

The headway d i s p l a y counter was c l e a r e d and then enabled

when t h e a c t u a l headway was ze ro . T h e r e a f t e r , i t d i sp layed t h e

d i f f e r e n c e i n d i s t a n c e t r a v e l e d by t h e two c a r s t o an accuracy of

about one f o o t p e r m i l e , The d i f f e r e n c e i n a c t u a l d i s t a n c e

t r a v e l e d by t h e two v e h i c l e s due t o imper fec t t r a c k i n g r e s u l t e d

i n accumulat ive e r r o r s , and t h e v e h i c l e had t o be r e t u r n e d t o

zero headway p e r i o d i c a l l y t o e v a l u a t e t h e magnitude of t h i s e r r o r .

The headway d i s p l a y was mounted above t h e dashboard j u s t below

t h e d r i v e r ' s normal l i n e of s i g h t t o provide e a s e of viewing

whi l e d r i v i n g (Figure 6.12).

With t h e fo l lowing c a r locked i n speed c o n t r o l , t h e l e a d c a r

d r i v e r was a b l e t o a r r i v e a t t h e d e s i r e d headway and minimize t h e

r e l a t i v e v e l o c i t y between t h e v e h i c l e s by observ ing t h e count and

F i g u r e 6 . 1 2 . Lead c a r c o n t r o l and d a t a r e c o r d i n g i n s t r u m e n t a t i o n . The c o u n t e r above t h e d a s h r e a d headway c o n t i n u o u s l y .

count ing r a t e of t h e headway coun te r and then app ly ing t h e l e a d

c a r ' s speed c o n t r o l , To i n i t i a t e a t r i a l t h e l e a d c a r d r i v e r

pushed a swi t ch which disengaged t h e l e a d c a r ' s speed c o n t r o l

and s imul taneous ly s t a r t e d t h e t imers and headway-change coun te r s .

When t h e s u b j e c t s responded, t h e i r r e s p e c t i v e coun te r s s top -

ped and h e l d t h e accumulated count , The l e a d v e h i c l e d r i v e r then

r ead t h e d a t a from t h e coun te r s on to a t a p e r e c o r d e r and c l e a r e d

them b e f o r e t h e beginning of t h e n e x t run .

A H e a t h k i t , GDA-47 , f i ve -channe l , p r o p o r t i o n a l r a d i o c o n t r o l

system was used f o r t h e t e l e m e t r y l i n k . The u n i t was modif ied t o

t r a n s m i t p u l s e d a t a and t o dec rease t h e d a t a t r ansmiss ion time

d e l a y i n h e r e n t i n t h e t ime d i v i s i o n m u l t i p l e x technique used. The

channel frame r a t e was i n c r e a s e d from 60 Hz t o 1 2 0 Hz. Thus, t h e

maximum de lay i n t r ansmiss ion of t h e s u b j e c t responses was 0.0083

seconds and t h e maximum d i s t ance -pu l se t r ansmiss ion r a t e was j u s t

under 120 p u l s e s p e r second which corresponds t o a maximum v e h i c l e

v e l o c i t y of about 80 mph.

Pwt-task lights were mounted on t h e l e f t and r i g h t s i d e of

t h e hood of t h e fo l lowing c a r (F igure 6 . 1 3 ) . These l i g h t s were

c o n t r o l l e d by t h e t a s k l i g h t t imer and t h e s u b j e c t s ' l e f t and

r i g h t t a s k l i g h t response swi t ches . The l i g h t s were tu rned on

one a t a t ime i n a random o r d e r wi th a v a r i a b l e t ime de lay between

o n s e t , and they remained on f o r f o u r seconds o r u n t i l bo th sub-

j e c t s had responded by depress ing t h e c o r r e c t swi tch .

Because of t h e p o s s i b i l i t y of accumulat ing e r r o r s , due t o

d i f f e r e n c e s i n l e a d c a r and fo l lowing c a r t r a c k s t o n t h e headway

coun te r a backup means of de termining t h e headway between t h e

v e h i c l e s was used. Spacing marks were a t t a c h e d t o t h e r e a r win-

dow of t h e l e a d c a r ; t h e s e were s e p a r a t e d a t d i s t a n c e s which were

predetermined such t h a t a t 200, 300, and 4 0 0 f e e t t h e image of

t h e fo l lowing v e h i c l e would f a l l j u s t w i t h i n t h e a p p r o p r i a t e rnark-

i n g s when they were viewed by t h e d r i v e r i n t h e rearv iew mi r ro r .

I n o r d e r t o e s t a b l i s h t h e accuracy of t h i s technique it was c r o s s -

F i g u r e 6 . 1 3 . The p a r t - t a s k l i g h t s mounted on t h e hood of t h e fo l lowing c a r , and t h e d r i v e r ' s response swi tches on t h e dash .

checked by t a k i n g v ideotape record ings of t h e fo l lowing v e h i c l e

whenever t h e l ead-ca r d r i v e r determined t h a t it was w i t h i n one

of t h e t h r e e d i s t a n c e s and t h a t he had a p p r o p r i a t e l y l o c a t e d t h e

headway based upon t h e markings. The t e l e v i s i o n monitor was

subsequent ly c a l i b r a t e d f o r t h e width of t h e fo l lowing v e h i c l e

image when it was p laced a t v a r i o u s known d i s t a n c e s from t h e l e a d

v e h i c l e . I n t h i s way a c o r r e l a t i o n could be ob ta ined between t h e

v ideotape recorded d i s t a n c e s of t h e l e a d c a r a g a i n s t those which

t h e d r i v e r e s t a b l i s h e d by means of t h e markings.

I t was found t h a t t h e mean a b s o l u t e e r r o r between t h e video-

t a p e measured d i s t a n c e s and those ob ta ined us ing t h e markings was

l e s s than 5 p e r c e n t . On t h i s b a s i s it was cons idered t h a t t h e

use of t h e markings on t h e v e h i c l e ' s r e a r window ( " r e a r l i g h t " )

provided a reasonably a c c u r a t e way t o e s t a b l i s h a f i x e d headway.

These markings were then r e t a i n e d on t h e v e h i c l e and used a s a

cross-check a g a i n s t t h e continuous headway d i s t a n c e count which

was ob ta ined from t h e headway d i s t a n c e up-down counter . When

t h e e r r o r between t h e s e two measurements appeared t o be i n excess

of about 5 pe rcen t t h e l e a d v e h i c l e d r i v e r r e c a l i b r a t e d t h e head-

way counter by coming a long s i d e t h e fo l lowing v e h i c l e and zero-

i n g t h e system.

Procedure. Two s u b j e c t s were used i n each t es t , One drove

t h e fo l lowing c a r and t h e o t h e r s a t i n t h e f r o n t passenger s e a t .

An experimenter was s e a t e d i n t h e r e a r s e a t , The d r i v e r opera ted

two swi tches l o c a t e d a t t h e t en - and two-o'clock p o s i t i o n s of t h e

s t e e r i n g wheel i n o r d e r t o respond t o t h e l e f t and r i g h t hood-

mounted l i g h t s . H e responded t o t h e d e t e c t i o n of changes i n head-

way a f t e r t h e l e a d c a r began t o c o a s t by depress ing a f o o t swi tch

wi th h i s l e f t f o o t , The passenger had a switchbox c o n t a i n i n g

t h r e e swi tches . The r i g h t thumb depressed one of two swi tches

corresponding t o t h e l e f t and r i g h t hood-mounted l i g h t s whenever

they appeard. The l e f t thumb depressed a t h i r d swi tch when he

d e t e c t e d t h a t t h e l e a d v e h i c l e had begun t o c o a s t .

The i n s t r u c t i o n s read p r i o r t o t h e s t a r t of t h e t e s t asked

t h e s u b j e c t s t o respond wi th t h e a p p r o p r i a t e swi tch whenever a

hood-mounted l i g h t appeared. I n a d d i t i o n they were t o depress

t h e t h i r d switch t o i n d i c a t e t h a t they were s u r e t h a t t h e l e a d

v e h i c l e had begun t o c o a s t and t h a t t h e headway between t h e two

c a r s was decreas ing . A number of p r a c t i c e runs were made f i r s t .

The t e s t was conducted on US-23, which i s a four- lane d iv ided

highway, between Ann Arbor and Toledo.

The d r i v e r of t h e fo l lowing c a r was t o l d t o fo l low t h e l ead

c a r a t a l l t imes and t o remain i n t h e r ight-hand l a n e of t h e road

un less an emergency d i c t a t e d o therwise . The fo l lowing c a r d r i v e r

a c t u a t e d t h e v e h i c l e speed c o n t r o l which brought t h e c a r speed up

t o 55 mph. The d r i v e r of t h e l ead c a r then e s t a b l i s h e d t h e

r e q u i r e d headway and locked i n h i s speed c o n t r o l . The v e h i c l e s

t r a v e l e d a t t h e e s t a b l i s h e d headway and a t t h e same speed f o r

between 1 0 and 45 seconds be fo re t h e l e a d v e h i c l e began t o c o a s t .

A s soon a s t h e l ead c a r d r i v e r depressed t h e swi tch which d i s -

engaged t h e speed c o n t r o l , t h e d a t a r ecord ing ins t rumenta t ion

was energized and both time and change i n v e h i c l e headway were

measured f o r t h e d r i v e r and t h e passenger. The n e x t t r i a l began

a f t e r t h e l ead c a r d r i v e r had again e s t a b l i s h e d headway between

t h e two c a r s , and t h e procedure was repeated .

Independent Var iables . Two independent v a r i a b l e s were inves-

t i g a t e d i n t h i s t e s t : (1) t h e d i s t a n c e between t h e v e h i c l e s

(headway) a t t h e s t a r t of c o a s t i n g and ( 2 ) t h e presence l i g h t

a r r a y s . Three va lues f o r t h e headway a t s t a r t of c o a s t i n g were

used: 200 f e e t , 300 f e e t , 4 0 0 f e e t .

Four presence l i g h t a r r a y s were used on t h e l e a d c a r :

(1) A s i n g l e l i g h t

( 2 ) A two lamp a r r a y

(3 ) A t h r e e lamp, t r i a n g u l a r a r r a y

( 4 ) A f o u r lamp a r r a y , wi th two lamps mounted a s i n t h e

two lamp a r r a y and two a d d i t i o n a l lamps mounted on

t h e v e h i c l e roof . These a r r a y s a r e shown i n Figure

179

6.14. A l l lamps were 4.0 i n c h e s i n d i ame te r w i t h r e d l e n s e s .

Lamp i n t e n s i t y was 7 candlepower. P r a c t i c e t r i a l s were conduc-

t e d w i t h a two lamp a r r a y i n which t h e lamps were spaced 37

i n c h e s edge- to-edge . Dependent V a r i a b l e , The dependent v a r i a b l e used i n t h i s

t e s t was t h e change i n t h e headway t h a t occu r red b e f o r e t h e sub-

j e c t s i n d i c a t e d t h a t t hey had n o t i c e d t h a t t h e l e a d v e h i c l e was

c o a s t i n g . Th i s d i s t a n c e was r e a d t o t h e n e a r e s t 1 . 0 f e e t .

Exper imenta l Design. I n t h i s t es t h a l f t h e s u b j e c t s c a r r i e d

o u t t h e tes t a t 200 and 300 f e e t , and t h e o t h e r h a l f a t 300 and

400 f e e t . T h e r e f o r e , t h e 300 f o o t d i s t a n c e p l u s one o t h e r was

used f o r each s u b j e c t .

There were two i n i t i a l d i s t a n c e s a t t h e s t a r t of c o a s t i n g

and f o u r lamp a r r a y s f o r each s u b j e c t . This t o t a l of e i g h t

a r r a y - d i s t a n c e combinat ions was p r e s e n t e d randomly, and two t r i a l s

were run w i t h each combinat ion, The e x c e p t i o n t o t h i s p rocedure

was t h a t t h e s i n g l e lamp a r r a y was always used on t r i a l s 1 5 , 1 6 ,

17 and 18 w i t h t h e two d i s t a n c e s be ing randomized among t h e s e

f o u r t r i a l s t w o - t r i a l b l o c k s a s w i t h t h e o t h e r a r r a y s . There

t h e n fo l lowed two more t r i a l s w i t h each of t h e a r r a y - d i s t a n c e com-

b i n a t i o n s f o r a r r a y s 2 , 3 and 4 on ly . Th i s means t h a t t h e r e was

a t o t a l of f o u r t r i a l s f o r each d i s t a n c e f o r a r r a y s 2 , 3 and 4 ,

and on ly two t r i a l s f o r t h e s i n g l e lamp a r r a y a t each of t h e two

d i s t a n c e s .

The r ea son f o r t h i s was t h a t t h e s i n g l e lamp a r r a y was

inc luded o n l y a s a c o n t r o l on t h e e f f e c t i v e n e s s of t h e experimen-

t a l p rocedure i n a s s e s s i n g t h e e f f e c t of t h e p re sence l i g h t a r r a y .

The s i m u l a t i o n s t u d i e s had c l e a r l y shown t h a t t h e s i n g l e l i g h t

a r r a y r e s u l t e d i n poore r s u b j e c t s e n s i t i v i t y t h a n o t h e r a r r a y s ;

t h e same should be t r u e i n t h i s s t u d y , i f s u b j e c t s a r e making

r e sponses based upon t h e l i g h t a r r a y s .

R e s u l t s , I n each array-headway combina t ion , f o r each t r i a l ,

t h e change i n headway t h a t occu r red b e f o r e t h e s u b j e c t responded

1.

b+)-728 i n .

L 7 0 i n .

58.0 i n .

i n .

F i g u r e 6 . 1 4 . The f o u r p resence l i g h t a r r a y s used i n t h e v e h i c l e headway change d e t e c t i o n t e s t .

was recorded . Ana lys i s of v a r i a n c e of t h e headway change d a t a

were performed t o de termine t h e e f f e c t of t h e Task ( d r i v e r and

passenger r e s p o n s e s ) , t h e Array ( exc lud ing a r r a y 1 f o r which

on ly p a r t i a l d a t a were a v a i l a b l e ) , t h e Headway, and t h e i r i n t e r -

a c t i o n s .

One a n a l y s i s of v a r i a n c e was conducted on t h e responses of

t h e 12 s u b j e c t s f o r whom t h e headway d i s t a n c e s were 200 and

300 f e e t (Table 6 , 9 ) . Th i s a n a l y s i s showed t h a t t h e r e was a s i g -

n i f i c a n t headway main e f f e c t and an a r r a y x headway i n t e r a c t i o n .

Another a n a l y s i s , f o r a s e p a r a t e group of 1 2 s u b j e c t s f o r

whom i n i t i a l headways were 300 and 400 f e e t (Table 6 . 1 0 ) , found

s i g n i f i c a n t main e f f e c t s f o r t h e headway and t h e a r r a y .

The t h i r d a n a l y s i s of v a r i a n c e was c a r r i e d o u t on t h e 300

f e e t headway d a t a u s i n g t h e d a t a f o r a l l 2 4 s u b j e c t s and showed

a s i g n i f i c a n t a r r a y main e f f e c t .

Newman-Keuls t e s t s were made on t h e means of t h e headway

change i n two, t h r e e and f o u r lamp a r r a y s a t each i n i t i a l head-

way (Table 6 . 1 1 ) . The median changes i n headway a t d e t e c t i o n

of c o a s t i n g a s a f u n c t i o n of t h e i n i t i a l headway f o r each a r r a y

( i n c l u d i n g t h e one lamp a r r a y ) , and t h e mean a r r a y e f f e c t i v e -

n e s s r a n k i n g s , a r e shown i n Table 6.12. This t a b l e shows t h e

l a r g e e f f e c t of t h e i n i t i a l headway upon c o a s t i n g d e t e c t i o n ,

a s measured by headway change ( A H ) . The e f f e c t of t h e a r r a y s

i n each headway c o n d i t i o n i s a l s o shown. I t w i l l be noted t h a t :

t h e median v a l u e s a r e about t h e same f o r each a r r a y a t 200 f e e t ;

a r r a y s 4 and 3 g i v e lower v a l u e s than 2 and 1 a t 300 f e e t ; 4 and 3

s u p e r i o r t o o t h e r s a t 4 0 0 feet. Also , a r r a y 1 provided lower

median v a l u e s than a r r a y 2 i n a l l c o n d i t i o n s , s u g g e s t i n g t h a t

t h e r e was an a r t i f a c t i n t h e t e s t s i t u a t i o n . I t appears l i k e l y

t h a t t h e o u t l i n e of t h e whi t e test v e h i c l e was v i s i b l e t o sub-

j e c t s , p a r t i c u l a r l y a t t h e n e a r e r d i s t a n c e s , which a f f e c t e d t h e

c o a s t i n g judgments wi th t h e one lamp a r r a y , i n which t h e lamp was

l o c a t e d a t t h e c e n t e r , r e a r of t h e c a r . I n t h e o t h e r a r r a y s lamps

TABLE 6.9. ANALYSIS OF VARIANCE OF THE CHANGE I N HEADWAY FOR 200 FEET AND 309 FEET INITIAL HEADWAY DISTANCES. DATA FOR SUBJECTS 1-12

Source SS - d f - MS - F - Between S u b i e c t s

--

Task ( T ) 2562.1 1 2562.1

S u b j e c t s i n Grps. 10 3161.1

Within S u b j e c t s

Array (A) 973.9 2 486.9

A x T 330.0 2 165-0

A x S u b j e c t s i n Grps. 20 490.7

Headway ( H ) 28262.5 1 28262.5

H x T 462.6 1 462.6

H x S u b j e c t s i n Grps. 10 1452.9

A x H 2011.8 2 1005.9

A x H x T 103.8 2 51.9

A x H x Subj . i n Grps. 20 250.9

* S i g n i f i c a n t a t p - -05 ** S i g n i f i c a n t a t p 5 .O1 -

TABLE 6.10. ANALYSIS OF VARIANCE OF THE CHANGE I N HEADWAY FOR 300 FEET AND 400 FEET INITIAL HEADWAY DISTANCES. DATA FOR SUBJECTS 13-24

Source

Between S u b j e c t s i n Grps.

Task ( T ) 1225 .1

S u b j e c t s i n Grps.

Wi th in S u b j e c t s i n Grps.

Array (A) 11407.8

A x T 224.8

A x S u b j e c t s i n Grps.

Headway (H) 36901.4

H x T 138.9

H x S u b j e c t s i n Grps.

A x H 3629.8

A x H x T 1956.8

A x H x S u b j e c t s i n Grps.

** S i g n i f i c a n t a t p 2 - 0 1

were mounted a t t h e edges, poss ib ly reducing v i s i b i l i t y of t h e

v e h i c l e o u t l i n e .

The mean e f f e c t i v e n e s s rankings i n Table 6.12 f o r each a r r a y

showed t h a t s u b j e c t s considered t h e one lamp a r r a y a s l e a s t e f f e c -

t i v e w i t h t h e two, t h r e e and f o u r lamp a r r a y s a s i n c r e a s i n g l y

e f f e c t i v e .

Table 6.13 shows t h e Weber r a t i o s f o r two, t h r e e and four

lamp a r r a y s a t each i n i t i a l headway. These va lues a r e i n d i c a t o r s

of d r i v e r s e n s i t i v i t y i n d e t e c t i n g c o a s t i n g and show t h a t t h i s

performance i s a func t ion of t h e lamp a r ray . The average scope

(Figure 6.15) of t h e s e n s i t i v i t y measure i s g r e a t e r f o r t h e two

lamp than t h e t h r e e lamp a r r a y , and l e a s t f o r t h e four lamp a r ray .

This means t h a t d e t e c t i o n of c o a s t i n g of t h e v e h i c l e w i t h t h e four

lamp a r r a y was l e a s t inf luenced by t h e i n i t i a l headway.

The d a t a i n d i c a t e t h a t t h e d r i v e r s ' s e n s i t i v i t y was g r e a t e s t

and most s t a b l e over d i s t a n c e f o r d e t e c t i o n of change i n headway

wi th a l e a d c a r , a t n i g h t , when t h e four lamp a r r a y was used.

The t r end i n t h e r e s u l t s , f o r comparable two, t h r e e and four

lamp a r r a y s , a r e q u i t e s i m i l a r t o those obta ined i n t h e simula-

t i o n s t u d i e s .

TABLE 6 . 1 1 . RESULTS OF NEWMAN-KEULS TESTS ON CHANGE I N HEADWAY MEANS I AT EACH I N I T I A L HEADWAY, FOR EACH ARRAY

A t 2 0 0 fee t : ho s i g n i f i c a n t d i f f e r e n c e s

A t 3 0 0 feet : A r r a y s 4 and 3 s i g n i f i c a n t l y be t te r t h a n 2

A t 4 0 0 feet : A r r a y 4 s i g n i f i c a n t l y be t t e r than 2

TABLE 6 . 1 2 . MEDIAN CHANGE I N HEADWAY (AH FEET) AS A FUNCTION OF I N I T I A L HEADWAY FOR ONE, TWO, THREE AND FOUR LAMP ARRAYS, AND MEAN EFFECTIVENESS RANKINGS

I n i t i a l H e a d w a y

Array 2 0 0 f ee t 3 0 0 f e e t 4 0 0 f e e t Me a n

R a n k i n g

TABLE 6 .13 . WEBER RATIOS ( A H / H ) FOR DETECTION OF CHANGE I N HEADWAY FOR TWO THREE AND FOUR LAMP ARRAYS

I n i t i a l H e a d w a y A r r a v Array 2 0 0 fee t 3 0 0 f e e t 4 0 0 f e e t ~e an"

- 2-Lamp Array -- 3-Lamp Array 0-0- 4-Lamp Array

200 300 400

I N I T I A L HEADWAY (FEET)

Figure 6.15. The Effect of Lamp Array Upon Weber

Ratios at Three Headway Distances

7 . COASTING SIGNAL ANALYSIS (TASK 7 )

INTRODUCTION. Vehicle s t o p s i g n a l s a r e a c t i v a t e d e i t h e r

when t h e brake peda l has been depressed a s u f f i c i e n t amount t o

c l o s e t h e c o n t a c t s of t h e s t o p l i g h t swi t ch o r when s u f f i c i e n t

p r e s s u r e has been developed i n t h e brake l i n e s t o c l o s e t h e

c o n t a c t s of a swi t ch s e n s i t i v e t o brake l i n e p r e s s u r e . Th i s

means t h a t t h e s t o p s i g n a l i s given on ly when t h e b rakes a r e

be ing a p p l i e d . Before s t e p p i n g on t h e brake p e d a l , a d r i v e r

u s u a l l y r e l e a s e s t h e a c c e l e r a t o r . I t has been cons idered f o r

some t ime t h a t a c c e l e r a t o r r e l e a s e could be used t o p rov ide

advance in fo rma t ion t o a fo l lowing d r i v e r s o t h a t he could pre-

pa re f o r brake a p p l i c a t i o n , This i n fo rma t ion could be p a r t i c u -

l a r l y impor tan t t o d r i v e r s i n a s t r eam of v e h i c l e s i n reduc ing

t h e i r t ime t o a c t u a t e t h e b rakes . I n a d d i t i o n , t h e r e i s a t t h e

p r e s e n t time no s i g n a l provided t o a fo l lowing d r i v e r t o i n d i -

c a t e t h a t a l e a d c a r i s c o a s t i n g wi th t h e a c c e l e r a t o r f u l l y

r e l e a s e d . Rockwell and Treiterer (1966) have shown t h a t coas t -

i n g d e t e c t i o n t ime can be reduced by t h e use of an amber s i g n a l

which appears when t h e a c c e l e r a t o r i s r e l e a s e d , compared t o a

no - s igna l c o n d i t i o n i n which t h e d r i v e r must r e l y on t h e i n t r i n -

s i c (pr imary) cues . Another s t u d y , by Crosley and Al len (1966) ,

h a s shown t h a t r e a c t i o n t ime of d r i v e r s t o t h e s t o p s i g n a l can

be reduced when an a c c e l e r a t o r - a c t u a t e d s i g n a l i s used.

The Guide Lamp Div i s ion of General Motors Corpora t ion

(Valasek, 1961) c a r r i e d o u t tes ts on a s t r eam of v e h i c l e s equip-

ped w i t h amber s i g n a l l i g h t s a c t u a t e d when t h e a c c e l e r a t o r was

r e l e a s e d . The c a r s were d r i v e n ove r 1000 miles and s u b j e c t i v e

e v a l u a t i o n s were made. I t was r e p o r t e d t h a t a f t e r a time fol low-

i n g d r i v e r s tended t o i g n o r e - t h e c o a s t i n g s i g n a l s because they

occu r red s o f r e q u e n t l y i n s i t u a t i o n s which r e q u i r e d no immediate

response .

The s tudy sugges t s some of t h e problems a s s o c i a t e d wi th a

s i g n a l l i n k e d t o o p e r a t i o n of t h e a c c e l e r a t o r . The a c c e l e r a t o r

i s used almost continuously f o r c o n t r o l l i n g speed, and it i s modulated over a wide range. For t h e s e reasons it can be expec-

t e d t h a t any s i g n a l coupled t o a c c e l e r a t o r opera t ion w i l l occur

wi th high frequency, p a r t i c u l a r l y i f t h e s i g n a l i s responsive

t o v a r i a t i o n s i n a c c e l e r a t o r p o s i t i o n . Acce le ra to r der ived s i g -

n a l s which a r e dependent upon t h e b ina ry s t a t e of a c c e l e r a t o r

a p p l i c a t i o n o r a c c e l e r a t o r r e l e a s e w i l l occur less o f t e n than

s i g n a l s which a r e der ived from a c c e l e r a t o r changes i n p o s i t i o n ,

b u t nonetheless they w i l l occur q u i t e f r equen t ly . There i s a l s o

no guarantee t h a t a c c e l e r a t o r r e l e a s e w i l l be followed by brake

pedal a c t u a t i o n , nor t h a t brake pedal a c t u a t i o n need fol low

wi th in a s h o r t time i n t e r v a l from t h e a c c e l e r a t o r r e l e a s e , These

d r i v e r a c t i o n s w i l l obviously be a func t ion of t h e perceived d r i v -

ing circumstances and t h e need t o o b t a i n varying l e v e l s of decel -

e r a t i o n ,

I t appears t o be c l e a r , t h e r e f o r e , t h a t while t h e r e a r e

p o t e n t i a l advantages t o s i g n a l s ac tua ted by t h e change i n posi-

t i o n o r t h e r e l e a s e of t h e a c c e l e r a t o r , t h e r e may a l s o be d e t r i -

mental and undes i rable e f f e c t s . Such a s i g n a l may be ambiguous

and poss ib ly a c t a s a d i s t r a c t i o n t o d r i v e r s . I t has a l ready

been i n d i c a t e d elsewhere (Mortimer, 1967) t h a t s i g n a l i n g systems

should be kep t a s simple a s p o s s i b l e and i n d i c a t e only those

messages which a r e of importance t o d r i v e r s and which a r e e a s i l y

i n t e r p r e t e d ,

Many of these ques t ions were r a i s e d i n a previous r e p o r t

(Nickerson e t a l . , 1968) which repor ted an experiment concerned

wi th t h e e f f e c t of va r ious p r o b a b i l i t i e s of t h e coas t ing s i g n a l

being followed by t h e s t o p s i g n a l upon subsequent d r i v e r r e a c t i o n

time t o t h e s t o p s i g n a l . That s tudy showed t h a t , un less t h e r e

was a high p r o b a b i l i t y (p>O. - 8 ) t h a t t h e s t o p s i g n a l would

fo l low t h e " e a r l y warning" s i g n a l , t h e r e was an i n c r e a s e i n t h e

number of f a l s e - p o s i t i v e braking responses. The study was a labor-

a t o r y experiment and d i d n o t i nvo lve a c t u a l d r i v i n g . I n t h i s

s t u d y a r e d u c t i o n i n r e a c t i o n time was u s u a l l y a s s o c i a t e d w i t h

t h e use of t h e e a r l y warning s i g n a l . However, t h e experiment

was r a t h e r f a r removed from a c t u a l d r i v i n g . S u b j e c t s shou ld

have been a b l e t o l e a r n t h e n a t u r e of t h e p r o b a b i l i t i e s asso-

c i a t e d w i t h t h e s t o p s i g n a l be ing fol lowed by t h e amber warning

s i g n a l , I n d r i v i n g , it would probably more d i f f i c u l t f o r

d r i v e r s t o de te rmine t h e l i k e l i h o o d of t h e s t o p s i g n a l appear-

i n g a f t e r t h e a c c e l e r a t o r r e l e a s e s i g n a l , a l though t h e g e n e r a l

t r a f f i c c o n f i g u r a t i o n should p rov ide some in fo rma t ion .

A s tudy was conducted t o o b t a i n an i n d i c a t i o n of t h e prob-

a b i l i t y of t h e b r a k e s be ing a p p l i e d fo l lowing a c c e l e r a t o r r e l e a s e ,

and a l s o t o o b t a i n d a t a on t h e d u r a t i o n of c o a s t i n g and d e c e l e r a -

t i o n , f o r which no e x t r i n s i c s i g n a l i s now g iven ,

Method. Coas t ing s i g n a l d a t a were c o l l e c t e d w i t h i n s t r u -

menta t ion i n s t a l l e d i n a 1968 Plymouth four-door sedan equipped

w i t h power b r a k e s , th ree-speed au toma t i c t r a n s m i s s i o n , and a

318 c u b i c i n c h V-8 e n g i n e , A f u n c t i o n a l b lock diagram of t h e

i n s t r u m e n t a t i o n i s shown i n F igu re 7 , l .

Data a r e recorded on a seven-channel , FM i n s t r u m e n t a t i o n

t a p e r e c o r d e r (Lockheed E l e c t r o n i c s Model 417) c a r r i e d i n t h e

t r u n k (F igu re 7.2) . Tapes, 3100 f e e t long , were recorded a t

1-7/8 inches p e r second t o provide about 5-1/2 hours of d a t a

p e r t a p e . The fo l lowing d a t a were recorded:

Channel 1 - 100-Hz time r e f e r e n c e

Channel 2 - V e l o c i t y / v e l o c i t y channel c a l i b r a t i o n v o l t a g e s

Channel 3 - Data sample e n a b l e g a t e

Channel 4 - A c c e l e r a t o r r e l e a s e p u l s e (20 m s ) Channel 5 - A c c e l e r a t o r a p p l i c a t i o n p u l s e (20 m s )

Channel 6 - Brake a p p l i c a t i o n p u l s e (20 m s )

Channel 7 - Brake r e l e a s e p u l s e (20 m s )

Data t a p e s were played back on t h e H S R I h y b r i d computer a t 30

inches pe r second , a s ix t een - to -one time r e d u c t i o n .

Figure 7.1. Vehicle instrumentation fo r coas t ing s i g n a l ana lys i s .

0.107v/mph Tach. . 7 b Hysteres is

Switch

i )

L w Pass F i l t e r

Accelerator + Osc i l l a to r Switch

1

Brake Switch

1 0

Logic

and

Pulse

Generators

I) Time Ref.

) Vel./ Cal.

Data Enable

Accel. Off

Accel. On

Brake On

Brake Off

F Accelerator Released Pulse

)

.)

Accelerator Applied Pulse k

Tape Recorder 8 LII)

Brake Applied Pulse A

Brake Released Pulse

Ign i t ion Switch

System Power and Tape Recorder Control

Figure 7.2. Coasting data recording instrumentation.

The computer sampled t h e d a t a on Channels 1 and 2 on command

from t h e d a t a sample p u l s e s on Channels 3 through 7 and computed

i n i t i a l and f i n a l c o a s t i n g v e l o c i t y , c o a s t i n g time, and c o a s t i n g

d i s t a n c e .

The 100-Hz time r e f e r e n c e recorded on Channel 1 was ob ta ined

from a c r y s t a l o s c i l l a t o r w i t h 0.005 p e r c e n t frequency s t a b i l i t y

over a tempera ture range of 0 t o 50 degrees c e n t i g r a d e . A p u l s e

i n t e g r a t i o n t echn ique , based on t h e z e r o c r o s s i n g s of t h e time

r e f e r e n c e , was used t o compute c o a s t i n g time. This y i e l d e d an

a c c u r a t e c o a s t i n g time measure which i s independent of t a p e speed.

The . v e l o c i t y s i g n a l was genera ted by a tachometer (Servo Tek

Model SA-757A2) mounted a t t h e t r ansmiss ion on one arm of a mechan-

i c a l d r i v e t e e d r i v e n by t h e speedometer p in ion . The o t h e r arm of

t h e t e e c a r r i e d t h e speedometer c a b l e . A second-order , low-pass

f i l t e r (6-Hz c u t o f f f requency) removed tachometer commutator n o i s e

and d r i v e t r a i n v i b r a t i o n n o i s e from t h e v e l o c i t y s i g n a l b e f o r e

it was recorded. The tachometer o u t p u t was c a l i b r a t e d on t h e road

a g a i n s t a Performance Measurements f i f th -whee l speedometer t o + 0.5 mph.

A h y s t e r e s i s swi tch genera ted t h e d a t a enab le g a t e from t h e

tachometer s i g n a l . This g a t e went h igh when t h e v e h i c l e v e l o c i t y

exceeded 20 mph, and it went low when t h e v e h i c l e v e l o c i t y dropped

below 1 mph, When t h e d a t a enab le g a t e was h i g h , t h e v e l o c i t y

s i g n a l was a p p l i e d t o Channel 2 of t h e r e c o r d e r through r e l a y 1

and t h e d a t a sample p u l s e g e n e r a t o r s were enabled . When t h e d a t a

enab le g a t e was low a v e l o c i t y channel c a l i b r a t i o n s i g n a l was

a p p l i e d t o Channel 2 and t h e d a t a sample p u l s e g e n e r a t o r s were

d i s a b l e d . Each time t h e d a t a enab le g a t e went low t h e f l i p - f l o p

changed s t a t e , and r e l a y 2 a l t e r n a t e l y s e l e c t e d a s t a b l e 0 mph o r

30 rnph c a l i b r a t i o n r e f e r e n c e v o l t a g e . These r e f e r e n c e v o l t a g e s

were used i n computer r e d u c t i o n of t h e d a t a t o c o r r e c t f o r changes

i n t h e v e l o c i t y channel c a l i b r a t i o n s through t h e e n t i r e system,

The l o g i c c i r c u i t s a s s o c i a t e d w i t h t h e a c c e l e r a t o r and brake

a p p l i c a t i o n / r e l e a s e pu l se g e n e r a t o r s were inc luded t o exclude

er roneous d a t a due t o a s u b j e c t " r i d i n g " t h e brake wi th t h e l e f t

f o o t . The a c c e l e r a t o r pu l se genera to r s were enabled only when

t h e brake peda l was r e l e a s e d , and t h e brake pu l se g e n e r a t o r s were

enabled only when t h e a c c e l e r a t o r was r e l e a s e d .

The s t a n d a r d brake l i g h t swi tch was used t o sense brake

a p p l i c a t i o n and r e l e a s e . The swi tch was a d j u s t e d t o o p e r a t e a t

a pedal displacement l e s s than t h a t r e q u i r e d t o b r i n g t h e brake

shoes i n c o n t a c t wi th t h e drums. A snap a c t i o n , momentary, push

b u t t o n swi tch a c t i v a t e d by a cam on t h e a c c e l e r a t o r l inkage was

mounted i n t h e engine compartment t o sense a c c e l e r a t o r app l i ca -

t i o n and r e l e a s e . I n t h i s arrangement t h e a c c e l e r a t o r swi tch

i n d i c a t e d t h a t t h e a c c e l e r a t o r was a p p l i e d a s long a s t h e t h r o t t l e

was on t h e h igh i d l e cam (engine c o l d ) . Thus, no d a t a sample

p u l s e s were genera ted u n t i l t h e engine warmed up and normal i d l e

speed was ob ta ined , Engine i d l e was a d j u s t e d t o manufac tu re r ' s

s p e c i f i c a t i o n , 6 0 0 rpm, w i t h t h e engine warm and t h e t r ansmiss ion

i n n e u t r a l ,

Procedure. The ins t rumented v e h i c l e was p u t i n t o s e r v i c e

wi th The Univers i ty of Michigan motor pool , and was d r i v e n by

i n d i v i d u a l s who were making t r i p s on Univers i ty bus iness . The

assignment of t h e v e h i c l e t o d r i v e r s was made by motor pool s t a f f

and, t h e r e f o r e , should have been on a random b a s i s . I n s i d e t h e

v e h i c l e was a set of b r i e f i n s t r u c t i o n s t o t h e d r i v e r and a t r i p

s h e e t which he was asked t o f i l l o u t both a t t h e s t a r t and a t

t h e completion of each t r i p (Appendix C - 1 ) . Each morning a mem-

b e r of t h e HSRI s t a f f removed t h e t ape from t h e t e s t v e h i c l e ,

r ep laced it wi th an unused t a p e , and checked t h e c a l i b r a t i o n of

t h e system. The d a t a t a p e was then r e t u r n e d t o H S R I , and when

a number of such t a p e s had been accumulated, they were run

through t h e hybr id computer system i n o r d e r t o p repare t h e d a t a

f o r a n a l y s i s .

Data were ob ta ined f o r 2 5 d i f f e r e n t d r i v e r s over 2 4 5 2 miles,

which were approximately broken down i n t o 295 mi les of c i t y

d r i v i n g , 2221 mi les of expressway o r freeway d r i v i n g , and 136

miles of r u r a l road d r i v i n g . These va lues a r e based on e s t i -

mates which were recorded by t h e d r i v e r s on t h e t r i p s h e e t and

from t h e odometer r ead ing of t h e v e h i c l e ,

Resu l t s . The d a t a t a p e s were analyzed by means of t h e HSRI

hybr id computer. An Ampex model FR1900, seven-channel t a p e

r e c o r d e r and playback machine was used t o p lay t h e d a t a i n t o t h e

AD-4 analog computer i n o r d e r t o process t h e s i g n a l s , which were

subsequent ly s e n t t o t h e IBM-1130 d i g i t a l computer. The method-

ology used i n d a t a r e t r i e v a l i s desc r ibed i n Appendix C-2 .

The d a t a were broken down t o show t h e fo l lowing f o u r d r i v e r

a c t i o n s : (1) a c c e l e r a t o r r e l e a s e fol lowed by a c c e l e r a t o r a p p l i -

c a t i o n , ( 2 ) a c c e l e r a t o r r e l e a s e fol lowed by brake a p p l i c a t i o n ,

(3 ) brake r e l e a s e fol lowed by a c c e l e r a t o r a p p l i c a t i o n , and ( 4 )

b rake r e l e a s e fol lowed by brake a p p l i c a t i o n . Each of t h e s e

d r i v e r a c t i o n s were ca tegor ized i n one of f o u r speed ranges:

0-4 mph, 5-30 mph, 31-55 mph, and 56-80 mph.

Within each speed ca tegory a d r i v e r a c t i o n was recorded

i n terms o f : (1) t h e c o a s t i n g time a s measured by t h e time dura-

t i o n when both t h e a c c e l e r a t o r and t h e brake a r e r e l e a s e d , ( 2 ) t h e

change i n v e l o c i t y t h a t occurred dur ing t h e c o a s t i n g p e r i o d , and

( 3 ) t h e change i n headway which would have occurred dur ing c o a s t -

i n g between t h e ins t rumented v e h i c l e and a fo l lowing v e h i c l e

which cont inued t o t r a v e l a t t h e same speed a s t h e t e s t c a r when

it began t o c o a s t . For each of t h e f o u r d r i v e r a c t i o n s frequency

d i s t r i b u t i o n s of t h e occurrence of each a c t i o n i n terms of c o a s t -

i n g t i m e , change i n v e l o c i t y and change i n headway were compiled.

Table 7 .1 shows t h e frequency wi th which each d r i v e r a c t i o n

occurred w i t h i n each of t h e f o u r speed ranges . Also shown i s

t h e t o t a l number of d r i v e r a c t i o n s upon which t h e percentages a r e

based w i t h i n each speed ca tegory . These d a t a provide an i n d i c a -

t i o n of t h e expected frequency of each of t h e f o u r d r i v e r a c t i o n s

TABLE 7.1. PERCENT OF EACH DRIVER CONTROL ACTION I N FOUR SPEED CATEGORIES

Driver ~ c t i o n ' Speed A+A A+B B+A B+B EN (mph) Actions

'A + A : Accelerator r e l ea se followed by acce le ra to r app l ica t ion

A - t A : Accelerator r e l ea se followed by brake appl icat ion

B + A : Brake appl icat ion followed by acce le ra to r appl icat ion

B + B : Brake app l ica t ion followed by brake appl icat ion

concerned wi th a c c e l e r a t o r and brake a p p l i c a t i o n . The d a t a show t h a t w i t h i n each speed ca tegory t h e expected frequency of each

a c t i o n i s somewhat d i f f e r e n t . For example, i n t h e lowest speed range , 0-4 mph, a c c e l e r a t o r r e l e a s e followed by a c c e l e r a t o r

a p p l i c a t i o n i s t h e most f r e q u e n t even t ; whereas, i n t h e speed

range 5-30 mph, a c c e l e r a t o r r e l e a s e followed by brake app l i ca -

t i o n occurs most o f t e n . T h e r e a f t e r , a s speed i n c r e a s e s accel -

e r a t o r r e l e a s e followed by a c c e l e r a t o r a p p l i c a t i o n again occurs

more f r e q u e n t l y than o t h e r even t s . Of p a r t i c u l a r i n t e r e s t i s

t h e expected frequency of a c c e l e r a t o r r e l e a s e being followed by

brake a p p l i c a t i o n which does n o t exceed 38 pe rcen t i n any speed

ca tegory . I f t h e d r i v e r a c t i o n , brake re lease-brake a p p l i c a t i o n

( B + B ) , i s a l s o added t o t h e a c c e l e r a t o r re lease-brake app l i ca -

t i o n (A+B) f r equenc ies , then t h e s e combined do n o t have a prob-

a b i l i t y g r e a t e r than 50 pe rcen t i n any speed ca tegory and con-

s i d e r a b l y l e s s i n some.

The d a t a i n Table 7 .1 i n d i c a t e , t h e r e f o r e , t h a t t h e prob-

a b i l i t y t h a t r e l e a s e of t h e a c c e l e r a t o r and r e l e a s e of t h e brake

w i l l be followed by brake a p p l i c a t i o n i s n o t g r e a t e r than 50 per-

c e n t and, t h e r e f o r e , occurs wi th a p r o b a b i l i t y t o be expected on

t h e b a s i s of chance. This means t h a t a c o a s t i n g o r d e c e l e r a t i o n

s i g n a l which is a c t u a t e d by r e l e a s e of t h e a c c e l e r a t o r pedal

dur ing c o a s t i n g cannot be considered an " e a r l y warning" s i g n a l

of t h e impending brake a p p l i c a t i o n , s i n c e t h e p r o b a b i l i t y t h a t

t h e brake , r a t h e r than t h e a c c e l e r a t o r , be app l i ed appears t o

be l e s s than 50 pe rcen t ,

Another a l t e r n a t i v e use of a c o a s t i n g s i g n a l i s t o i n d i c a t e

t h a t t h e v e h i c l e i s i n a d e c e l e r a t i n g mode f o r which t h e r e i s ,

a t t h e moment, no e x t r i n s i c s i g n a l given t o a fo l lowing d r i v e r .

I n o r d e r t o e v a l u a t e t h e s i g n a l i n those terms n o t only were d a t a

c o l l e c t e d i n which t h e frequency of each d r i v e r a c t i o n was mea-

su red , b u t a l s o t h e time, v e l o c i t y change and change i n headway

which occurred dur ing each c o a s t i n g pe r iod were measured.

Figure 7.3 shows t h e cumulative pe rcen t d i s t r i b u t i o n of t h e

c o a s t i n g d u r a t i o n s f o r t h e d r i v e r a c t i o n i n which a c c e l e r a t o r

r e l e a s e was followed by a c c e l e r a t o r a p p l i c a t i o n (A+A) f o r each

of t h e four speed c a t e g o r i e s . I t w i l l be noted t h a t t h e longes t

c o a s t i n g times f o r t h i s d r i v e r a c t i o n a r e i n t h e speed ca tegory

5-30 mph and t h e lowest t imes a r e found i n t h e h i g h e s t speed

ca tegory , 56-80 mph. However, t h e d i f f e r e n c e between t h e speed

c a t e g o r i e s i n c o a s t i n g t imes a r e l e s s than 1 second. The f i g u r e

a l s o shows t h a t 90 pe rcen t of c o a s t i n g t imes f o r a l l speed ca te -

g o r i e s a r e below 4 and 5 seconds, and t h a t 50 pe rcen t of t h e s e

a r e l e s s than 1 .0 -1 .6 seconds. F igures 7 . 4 and 7.5 show t h e

c o a s t i n g time cumulative d i s t r i b u t i o n s f o r t h e f o u r speed ranges

f o r t h e o t h e r t h r e e d r i v e r a c t i o n s (A+B, B+A, B+B) i n a s i m i l a r

manner. F igures 7.3 and 7.4 have q u i t e s i m i l a r t r e n d s i n d i c a t i n g

t h a t coas t ing d u r a t i o n s a r e much t h e same whether t h e d r i v e r

r e a p p l i e s t h e a c c e l e r a t o r o r t h e brake fol lowing a c c e l e r a t o r

r e l e a s e . Figure 7.5 shows t h a t t h e two d i s t r i b u t i o n s of acce l -

e r a t o r o r brake a p p l i c a t i o n fo l lowing brake r e l e a s e a r e a l s o

s i m i l a r t o each o t h e r , b u t t h e s e two d i f f e r from t h e d i s t r i b u -

t i o n s of even t s fo l lowing a c c e l e r a t o r r e l e a s e i n t h a t t h e time

d u r a t i o n s a r e s h o r t e r .

I t i s worth no t ing t h a t i n Figure 7.4 a c c e l e r a t o r r e l e a s e

i s o c c a s i o n a l l y followed by brake a p p l i c a t i o n a number of seconds

l a t e r , This means t h a t brake a p p l i c a t i o n , fo l lowing r e l e a s e of

t h e a c c e l e r a t o r , was n o t done r a p i d l y , which sugges t s t h a t t h e

need t o apply t h e brakes was n o t urgent . I n only 1 4 ~ e r c e n t ' of

the occas ions when a c c e l e r a t o r r e l e a s e was followed by brake

a p p l i c a t i o n were t h e brakes a p p l i e d w i t h i n 0 . 5 seconds fo l lowing

a c c e l e r a t o r r e l e a s e . Evident ly t h e s i t u a t i o n d i d no t demand a

' ~ h i s va lue was obta ined from a c o a s t i n g t i m e d i s t r i b u t i o n

( n o t shown) i n which t h e d a t a were ca tegor ized by 0 . 1 seconds.

MPH ------- 56-80 31-55 --- 5-30 -- 0-4

C O A S T I N G T I M E (SECONDS)

Figure 7 . 3 . Cumulative percent coasting time d i s t r i b u t i o n , acce lera tor re lease followed by accelerator appl ica t ion , i n four speed categories .

MPH ------- 56-80 31-55 . . - 5-30 -- 0-4

COASTING TIME (SECONDS)

F i g u r e 7 . 4 . Cumulative p e r c e n t c o a s t i n g t ime d i s - t r i b u t i o n , a c c e l e r a t o r r e l e a s e fol lowed by brake a p p l i c a t i o n , i n f o u r speed c a t e g o r i e s .

MPH ------ 5 6 - 8 0 - 3 1 - 5 5 -.- 5-30 - - 0 4

C O A S T I N G T I M E (SECONDS)

Figure 7 .5 . Cumulative percent coast ing time d i s - t r i b u t i o n s f o r brake re l ease followed by acce lera tor and brake appl ica t ion , i n four speed ca tegor ies .

r a p i d brake a p p l i c a t i o n s i n c e most d r i v e r s can t r a n s f e r t h e f o o t

from t h e a c c e l e r a t o r t o t h e brake i n less than 0 .5 seconds

(Belzer & Huffman, 1966; F i s h e r , 1968) . The re fo re , i n a t l e a s t

86 p e r c e n t of t h o s e occas ions i n which brake a p p l i c a t i o n fol lowed

a c c e l e r a t o r r e l e a s e t h e d r i v e r d i d n o t f e e l t h e r e was a need t o

do t h i s q u i c k l y , and cor respondingly t h e need t o provide e a r l y

warning in fo rma t ion t o a fo l lowing d r i v e r would be reduced. Con-

s i d e r i n g t h i s t o g e t h e r w i t h t h e e a r l i e r d a t a shown i n Table 7 . 1 ,

i n which it was no ted t h a t less than 38 p e r c e n t of t h e e v e n t s , i n

any speed ca t egory , were t h o s e i n which b rak ing fol lowed a c c e l -

e r a t o r r e l e a s e , it could now be sugges ted t h a t i n a t l e a s t 86 per-

c e n t of t h o s e (A+B) even t s t h e r e was l i t t l e need f o r an e a r l y

warning s i g n a l . Th i s would f u r t h e r reduce t h e p r o b a b i l i t y t h a t

t h e e a r l y warning s i g n a l could have r e l evance i f it appeared

whenever t h e v e h i c l e was c o a s t i n g . I t w i l l a l s o be noted from

F igures 7.3-7.5 t h a t t h e frequency w i t h which a c o a s t i n g s i g n a l

would appear f o r r e l a t i v e l y s h o r t d u r a t i o n s of about 5 seconds

o r less i s q u i t e h igh . This sugges t s t h a t t h e change i n v e l o c i t y

o r t h e d e c e l e r a t i o n which would occur f r e q u e n t l y may be q u i t e

sma l l .

F igu res 7.6-7.8 show t h e cumulat ive p e r c e n t d i s t r i b u t i o n s

of t h e change i n speed t h a t a c t u a l l y occurred w i t h t h e t e s t

v e h i c l e d u r i n g t h e c o a s t i n g p e r i o d s f o r each d r i v e r e v e n t i n each

i n i t i a l speed ca t egory a t t h e s t a r t of c o a s t i n g . A s expec ted ,

t h e g r e a t e s t changes i n speed occurred i n t h e h igh speed c a t e g o r i e s

and decreased w i t h dec reas ing v e l o c i t y a t t h e s t a r t of c o a s t i n g .

I t w i l l a l s o be no ted t h a t most f r e q u e n t l y t h e change i n speed

was 4 rnph o r less. There was aga in a d i f f e r e n c e i n magnitude of

speed change i n t h e d r i v e r a c t i o n s which were preceded by a c c e l -

e r a t o r r e l e a s e a s compared w i t h t h o s e preceded by brake peda l

r e l e a s e . I n t h e l a t t e r i n s t a n c e t h e changes i n speed were con-

s i d e r a b l y less, a s expec ted from t h e lower time d u r a t i o n s of

c o a s t i n g f o r t h e s e e v e n t s (F igu re 7 . 5 ) .

CHANGE I N S P E E D DURING COASTING (MPH)

Figure 7 . 6 . Cumulative percent change i n speed, acce lera tor re lease followed by accelera- t o r appl icat ion, i n four speed categories .

MPH ------ 56-80 3 1- 5 5 - - 5-30 -- 0-4

CHANGE I N S P E E D DURING C O A S T I N G (MPH)

F i g u r e 7 . 7 . Cumulative p e r c e n t change i n speed d i s t r i b u t i o n , a c c e l e r a t o r r e l e a s e fol lowed by brake a p p l i c a t i o n , f o r f o u r speed c a t e g o r i e s .

CHANGE I N S P E E D D U R I N G C O A S T I N G (MPH)

Figure 7 .8 . Cumulative percent change i n speed d i s t r i b u t i o n , brake re l ease followed by acce lera tor and brake appl ica t ion , f o r four speed ca tegor ies .

F i g u r e s 7.9-7.11 show t h e cumulat ive percentage d i s t r i b u -

t i o n s f o r t h e change i n headway t h a t would have occu r red d u r i n g

t h e c o a s t i n g p e r i o d between t h e t es t c a r and a fo l lowing v e h i c l e

which main ta ined t h e same speed a s t h e t e s t v e h i c l e a t t h e begin-

n i n g of t h e c o a s t i n g pe r iod . These d a t a a r e impor t an t i n terms

of t h e s a f e t y i m p l i c a t i o n of t h e change i n d i s t a n c e between two

v e h i c l e s t h a t might occur when a l e a d v e h i c l e begins t o c o a s t ,

f o r which no e x t r i n s i c s i g n a l i s now g iven , Note t h a t i n F igu res

7.9-7.11 f r e q u e n c i e s of 0 o r p o s i t i v e v a l u e s of change i n head-

way i n d i c a t e t h a t t h e headway e i t h e r d i d n o t change o r a c t u a l l y

i n c r e a s e d , due t o c o n s t a n t v e l o c i t y d u r i n g c o a s t i n g o r an i n c r e a s e

i n speed by t h e l e a d v e h i c l e . Th i s i s shown t o have occu r red i n

a low percentage of c a s e s i n F igu res 7.6-7.5. F igu res 7.9 and

7.10 show t h a t t h e change i n headway was r a r e l y reduced by a s

much a s 15 f e e t . The r e a l importance of t h i s change i n d i s t a n c e

can on ly be a s s e s s e d from a knowledge of t h e fo l lowing-d i s t ances

between v e h i c l e s , which would t end t o be g r e a t e r a t h i g h e r speeds .

Table 7.2 shows t h e 90 th p e r c e n t i l e v a l u e s f o r t h e c o a s t i n g

t i m e , t h e change i n speed and t h e change i n headway which were

o b t a i n e d from F igu res 7.3-7.11, f o r each of t h e f o u r speed ranges

and t h e d r i v e r c o n t r o l a c t i o n s . The t a b l e i n d i c a t e s t h a t , i n 90

p e r c e n t of t h e c o a s t i n g occas ions , c o a s t i n g d u r a t i o n d i d n o t

exceed 5.0 seconds , t h e speed change was n o t g r e a t e r than a reduc-

t i o n of 4 . 0 mph and t h e consequent change i n headway d i d n o t

exceed a r e d u c t i o n of 15 f e e t . These v a l u e s a r e a l s o dependent

upon t h e speed ca t ego ry and a r e g e n e r a l l y of n e g l i g i b l e magnitude

i n t h e 0-4 mph c a t e g o r y , w i th l a r g e r e f f e c t s a t h i g h e r speeds .

The t a b l e a l s o shows q u i t e c l e a r l y t h a t c o a s t i n g fo l lowing brake

r e l e a s e has l i t t l e e f f e c t on v e h i c l e speed o r headway change and

means t h a t a s i g n a l e x p l i c i t l y deno t ing t h i s c o n d i t i o n would pro-

v i d e l i t t l e in fo rma t ion . Somewhat more in fo rma t ion would be g iven

by a s i g n a l which i n d i c a t e s a c c e l e r a t o r r e l e a s e fol lowed e i t h e r by

a c c e l e r a t o r o r b rake a p p l i c a t i o n .

>-+ 1 0 - 0 -10 -20 -30 -40 -50 -60 -70 -80

CHANGE I N HEADWAY DURING COASTING ( F E E T )

Figure 7 . 9 . Cumulative percent change in headway dis t r ibut ion, accelerator release followed by accelerator application, for four speed categories.

MPH ------ 56-80 - 31-55 -a- 5-30 - - 0-4

>" + l o 0 -10 -20 -30 -40 -50 -60 -70 -80. - CHANGE I N HEADWAY DURING C O A S T I N G (FEET)

Figure 7.10. Cumulative percent change in headway distribution, accelerator release followed by brake application, for four speed categories.

> 0 - - 1 0 - 2 0 - 3 0 - 1 0 - 2 0 - 3 0 - 40 - 4 0 >O - CHANGE IN HEADWAY DURING COASTING (FEET)

Figure 7 . 1 1 . Cumulative percent change i n headway d i s t r i b u t i o n , brake r e l ease followed by acce lera tor and brake appl ica t ion , f o r four speed ca tegor ies .

TABLE 7.2. 90TH PERCENTILE COASTING TIME, CHANGE I N SPEED AND CHANGE I N HEADWAY I N FOUR SPEED RANGES FOR FOUR DRIVER CONTROL ACTIONS

Coas t ing T i m e ( seconds) Dr ive r MPH MPH MPH MPH Action 6-4 5 - 30 31-55 56-80

Change I n Speed During Coas t ing (mph)

Dr ive r MPH MPH MPH MPH Action 0-4 5-30 31-55 56 -80

A + A (-1 -2.0 -3 .0 -4 .0

Change I n Headway During Coas t ing ( f e e t )

Dr ive r MPH MP H MP H MPH Act ion 0-4 5 -30 31-55 56 -80

The r e s u l t s of F igures 7.3-7,11 a r e summarized i n Figures

7.12-7.14, which a r e based on t h e sum of a l l f o u r d r i v e r a c t i o n s

i n each speed category.

The d a t a i n d i c a t e t h a t it would be c l e a r l y undes i rable t o

have a s i g n a l appearing on t h e r e a r of t h e v e h i c l e whenever t h e

v e h i c l e was coas t ing . This i s because such s i g n a l s would f r e -

quen t ly occur f o r q u i t e s h o r t time per iods (1 -2 seconds, Figure

7.12) when t h e l e a d v e h i c l e changes i t s v e l o c i t y by only a smal l

amount (0-2 mph, Figure 7.13) and a l s o because t h e s i g n a l i s f o l -

lowed by a brake a p p l i c a t i o n i n less than 50 pe rcen t of occas ions ;

and i n 86 ,pe rcen t of those even t s t h e r e was no need t o apply t h e

brakes wi th in 1/2 second. Therefore , i n n o t more than 7 percen t

of d r i v e r c o n t r o l a c t i o n s could t h e coas t ing s i g n a l be considered

a s an e a r l y warning s i g n a l of impending braking. A s i g n a l a c t i v -

a t e d whenever the a c c e l e r a t o r was r e l e a s e d dur ing c o a s t i n g would

provide r e l a t i v e l y l i t t l e information and could d i s t r a c t d r i v e r s

from p o t e n t i a l l y important s t i m u l i .

However, t h e d a t a a l s o i n d i c a t e d t h a t t h e longer coas t ing

per iods can r e s u l t i n v e l o c i t y changes which produce q u i t e l a r g e

reduc t ions i n v e h i c l e speed and, consequently, i n t h e headway

wi th a fo l lowing v e h i c l e , The d a t a c o l l e c t e d i n Task 6.0 of t h i s

p r o j e c t have shown t h a t t h e d r i v e r ' s s e n s i t i v i t y f o r d e t e c t i o n of

c o a s t i n g r e q u i r e s a change i n headway of about 0.15 of t h e i n i t i a l

headway (Table 6.13) i n n i g h t d r iv ing . An a n a l y s i s has suggested

t h a t t h e necessary change i n headway f o r d e t e c t i o n i s 0.15 of t h e

i n i t i a l headway (Hoffman, 1968) . The d r i v e r ' s a b i l i t y t o d e t e c t

c o a s t i n g has an impl ica t ion i n determining t h e need f o r a coas t -

i n g s i g n a l . For example, t h e d a t a i n Table 7.2 i n d i c a t e t h a t t h e

90th p e r c e n t i l e expected reduc t ion i n headway dur ing c o a s t i n g ,

when a c c e l e r a t o r r e l e a s e i s followed by a c c e l e r a t o r a p p l i c a t i o n

i n t h e speed range 31-55 mph, would n o t be g r e a t e r than 15 f e e t .

If it i s assumed t h a t another v e h i c l e was fo l lowing a t two-car

l e n g t h s , about 40 f e e t , t h e c o a s t i n g of t h e l e a d v e h i c l e would

be expected t o be d e t e c t e d when t h e headway had been reduced by

MPH

0 1 2 3 4 5 6 7 8 9 1 0 1 1 1 2 1 3 1 4 1 5 1 6

COASTING TIME (SECONDS)

Figure 7.12. Cumulative percent coas t ing time d i s t r i b u t i o n ac ro s s d r i v e r a c t i o n s , f o r four speed ca t ego r i e s .

MPH

CHANGE IN SPEED DURING COASTING (MPH)

F i g u r e 7 .13 . Cumulative p e r c e n t change i n speed d i s t r i b u t i o n , a c r o s s d r i v e r a c t i o n s , f o r f o u r speed c a t e g o r i e s .

>+lo - 0 -10 - 2 0 -30 - 4 0 -50 -60 -70

CHANGE I N HEADWAY DURING COASTING ( F E E T )

F i g u r e 7 . 1 4 . Cumulative p e r c e n t change i n headway d i s t r i b u t i o n , a c r o s s d r i v e r a c t i o n s , f o r f o u r speed c a t e g o r i e s .

s i x f e e t , us ing AH=0.15 f o r t h e d r i v e r ' s s e n s i t i v i t y . There-

f o r e , t h e d r i v e r would become aware of t h e coas t ing of t h e l ead

v e h i c l e w e l l be fo re t h e end of t h e c o a s t i n g per iod i n t h i s par-

t i c u l a r s i t u a t i o n . Other such analyses could be c a r r i e d o u t f o r

va r ious i n i t i a l headways and v e l o c i t i e s a t t h e time of coas t ing .

On t h e b a s i s of t h e r e s u l t s it i s concluded t h a t t h e coas t -

i n g s i g n a l would n o t provide d r i v e r s wi th e a r l y warning of brake

a p p l i c a t i o n . Furthermore, t h e d a t a have shown t h a t t h e coas t ing

s i g n a l would appear wi th high frequency f o r s h o r t time per iods

dur ing which t h e v e l o c i t y of t h e v e h i c l e would be reduced by

smal l amounts. I t appears t h a t l i t t l e reduct ion i n rear-end

a c c i d e n t s would r e s u l t from a s i g n a l i n d i c a t i n g c o a s t i n g when-

ever t h e a c c e l e r a t o r was r e l e a s e d , p r i o r t o t h e a p p l i c a t i o n of

t h e brakes and t h e appearance of t h e s t o p s i g n a l , On t h e con-

t r a r y , a s was hypothesized i n a previous r e p o r t (Mortimer, 1967) ,

a s i g n a l of t h a t type w i l l produce l i t t l e informat ion , i s l i k e l y

t o be d is regarded by d r i v e r s (Valasek, 1961) and could d i s t r a c t

t h e d r i v e r from more important s i g n a l s and o t h e r s t i m u l i . The

e f f e c t t h a t it would have upon t r a f f i c flow i s open t o specula-

t i o n .

However, t h e d a t a a l s o showed t h a t , while 9 0 pe rcen t of

c o a s t i n g per iods a r e 5 seconds o r less, it must fol low t h a t i n

1 0 pe rcen t of such i n s t a n c e s coas t ing pe r iods a r e g r e a t e r than

5 seconds. I n long c o a s t i n g pe r iods t h e p o t e n t i a l l y l a r g e reduc-

t i o n s i n headway should be d e t e c t e d by fo l lowing c a r d r i v e r s

be fo re t h e l e a d v e h i c l e d r i v e r a p p l i e s t h e brakes (and s t o p s i g -

n a l ) o r r e a p p l i e s t h e a c c e l e r a t o r , However, t h e r e w i l l be i n f r e -

quent i n s t a n c e s when long coas t ing pe r iods occur which a r e detec-

t e d l a t e by d r i v e r s of fo l lowing v e h i c l e s , Such s i t u a t i o n s could

be hazardous and r e s u l t i n rear-end c o l l i s i o n s , For t h i s reason i t may be recommended t h a t a s i g n a l be provided t o a l e r t follow-

i n g d r i v e r s t o such s i t u a t i o n s . This means t h a t a s i g n a l should

be given when t h e coas t ing time has exceeded about 5 seconds, and

only on those occas ions , Based on t h e s e d a t a such s i g n a l s would

occur less than 1 0 pe rcen t of t h e time when v e h i c l e s ' a r e i n a coas t ing mode and, hence, would n o t cause ambiguous d i s t r a c t i o n s .

I t i s proposed t h a t t h e s imples t mode of implementing such a

s i g n a l would be t o a c t u a t e t h e v e h i c l e s t o p l i g h t s . Also, t h e

s i g n a l should remain a c t i v a t e d u n t i l t h e a c c e l e r a t o r i s reapp l i ed .

PART I V , DEVELOPMENT OF RECOMMENDATIONS DISCUSSION

The preceding s e c t i o n s have o u t l i n e d t h e g e n e r a l problem

of rear -end c o l l i s i o n s and t h e re levance of v e h i c l e r e a r l i g h t -

i n g and s i g n a l i n g . The b a s i s f o r conducting each s t u d y and t h e

exper imenta l o r a n a l y t i c a l approaches t h a t were used have been

desc r ibed . The r e s u l t s of each t a s k were d i s c u s s e d t o show

how they might be a p p l i e d . I n t h i s s e c t i o n a l l t h e f i n d i n g s

w i l l be d i s c u s s e d i n o r d e r t o show t h e r a t i o n a l e f o r any recom-

mendations f o r v e h i c l e l i g h t i n g t h a t may be made.

SYSTEM CODING. The s t u d i e s c a r r i e d o u t i n Task 1 of t h i s

program have confirmed p rev ious f i n d i n g s (Rockwell and Banasik,

1968; Mortimer, 1969a; 1969b) t h a t t h e r e a r e o t h e r e f f e c t i v e

coding t echn iques than those now used t h a t may be a p p l i e d t o

r e a r l i g h t i n g and s i g n a l i n g systems. System e f f e c t i v e n e s s was

measured by a number of d r i v e r performance v a r i a b l e s inc lud ing :

r e a c t i o n time t o t h e s i g n a l , e r r o r s i n s i g n a l i d e n t i f i c a t i o n ,

t h e number of s i g n a l s missed, and s u b j e c t i v e e v a l u a t i o n s . Each

of t h e s e c r i t e r i a a r e cons idered r e l e v a n t and impor tan t i n

de termining s i g n a l system e f f e c t i v e n e s s , The e f f e c t i v e n e s s of

a s i g n a l i n a l e r t i n g a d r i v e r can be measured by t h e time

r e q u i r e d by a fo l lowing d r i v e r t o d e t e c t t h a t a s i g n a l i s be ing

shown on a v e h i c l e ahead of him, i r r e s p e c t i v e of t h e need of

t h a t d r i v e r t o make an immediate response t o t h a t s i g n a l . A

s h o r t r e a c t i o n time w i l l p o t e n t i a l l y a l low him a d d i t i o n a l t ime

i n which t o reach a d e c i s i o n concerning h i s own a c t i o n s and t o

a t t e n d t o o t h e r s t i m u l i . Reductions i n d r i v e r response t ime

a r e a l s o impor tan t i n t h o s e c i rcumstances where a r a p i d r e a c t i o n

on t h e p a r t of a fo l lowing d r i v e r i s needed t o avoid a rear-end

c o l l i s i o n . S i g n a l systems must a l s o be capable of p r e s e n t i n g

s i g n a l s t h a t a r e e a s i l y i n t e r p r e t a b l e by fo l lowing d r i v e r s and

it is r e l e v a n t t o c o n s i d e r s i g n a l i d e n t i f i c a t i o n a s ano the r per-

formance c r i t e r i o n . I t i s obv ious ly impor t an t t h a t s i g n a l s be

pe rce ived by fo l lowing d r i v e r s s i n c e a s i g n a l which i s missed

i n c r e a s e s t h e p o t e n t i a l f o r a rear -end c o l l i s i o n . I t would be

expec ted t h a t s i g n a l s which have a h igh a r o u s a l c a p a b i l i t y would

have low d r i v e r d e t e c t i o n t imes and be d e t e c t e d on most occas ions

on which t h e y a r e shown. The e v a l u a t i o n s e l i c i t e d from d r i v e r s

a r e f u r t h e r s o u r c e s of u s e f u l d a t a and have been used e x t e n s i v e l y

i n c o n j u n c t i o n w i t h t h e o t h e r measures i n t h e s e s t u d i e s .

One of two exper iments conducted i n t h i s program concerned

w i t h t h e e v a l u a t i o n of r e a r l i g h t i n g system coding concep t s

found t h a t when a h igh s i g n a l - p r e s e n c e l i g h t i n t e n s i t y r a t i o

(13: 1) was used w i t h h igh s i g n a l i n t e n s i t y (91cp) , o v e r a l l mean

r e a c t i o n time was 0.992 seconds , For t h e same i n t e n s i t y r a t i o

b u t lower s i g n a l i n t e n s i t y (35 c p ) , o v e r a l l mean r e a c t i o n time

a c r o s s t h e f i v e l i g h t i n g systems i n t h e o t h e r exper iment was

1.039 seconds (Table 1 . 2 ) . For t h e same f i v e systems t h e r e s u l t s

of a p rev ious s i m i l a r t e s t (Mortimer, 1969b) showed o v e r a l l mean

r e a c t i o n times of 1.063 seconds. I n t h e l a t t e r t e s t t h e s i g n a l -

p re sence l i g h t i n t e n s i t y r a t i o was 5:1, w i t h s i g n a l i n t e n s i t y

be ing 35 cp. These t h r e e r e s u l t s i n d i c a t e t h a t t h e r e i s a bene-

f i t d e r i v e d from t h e use of h igh a b s o l u t e i n t e n s i t i e s and h i g h

s i g n a l - p r e s e n c e l i g h t i n t e n s i t y r a t i o s and t h a t when s i g n a l i n t e n -

s i t y i s t h e same (35 cp) t h e 1 3 : l r a t i o provided s l i g h t l y dec reased

r e a t i o n times compared t o t h e 5 : l i n t e n s i t y r a t i o .

I n t h e system e v a l u a t i o n s it was found t h a t t h e r e were no

s i g n i f i c a n t d i f f e r e n c e s between t h e p r e s e n t system concept ( sys -

tem 1) and expe r imen ta l systems i n r e a c t i o n time t o t h e s t o p

s i g n a l . The same r e s u l t was found i n t h e e a r l i e r s t u d y (Mortimer,

1969b) . This should n o t be t aken t o i n d i c a t e , however, t h a t t h e

s t o p s i g n a l of system 1 was a s e f f e c t i v e a s t h a t of t h e e x p e r i -

menta l systems. One r eason i s t h a t an e a r l i e r s t u d y (Mortimer,

1 9 6 9 a ) , conducted i n t h e form of a s t a t i c s i m u l a t i o n u s i n g a c t u a l

v e h i c l e s , found t h a t some of t h e expe r imen ta l systems used i n t h e

dynamic s t u d i e s r e p o r t e d h e r e d i d p rov ide dec reased r e a c t i o n times

i n t h e s t o p s i g n a l mode compared t o t h e p r e s e n t system, I n

a d d i t i o n , t h e d a t a from a l l of t h e s e s t u d i e s have shown t h a t i n

t h e t u r n - s t o p mode, i n which a t u r n s i g n a l appears i n i t i a l l y

and i s fol lowed by t h e s t o p s i g n a l , exper imenta l systems pro-

v ided s i g n i f i c a n t l y reduced response times,

The system c u r r e n t l y employed on many European v e h i c l e s

i n which t h e presence and t h e s t o p s i g n a l a r e shown by one lamp

which i s s e p a r a t e d from an amber t u r n s i g n a l was n o t e v a l u a t e d

i n any of t h e s e s t u d i e s , The reason f o r t h i s was t h a t , on an

a n a l y t i c a l b a s i s , it d i d n o t seem t h a t such a system should

provide improved performance compared t o a number of t h e e x p e r i -

mental systems t h a t were s e l e c t e d , Because of t h e importance of

t h e s t o p s i g n a l , e i t h e r when appear ing a lone o r preceding o r f o l -

lowing a t u r n s i g n a l , it was cons idered t h a t it should be sepa-

r a t e d o u t from o t h e r s i g n a l s . The r e s u l t s of t h e s e s t u d i e s have

tended t o confirm t h i s f i n d i n g p a r t i c u l a r l y wi th regard t o t h e

d u a l s i g n a l p r e s e n t a t i o n s ( t u r n - s t o p , s t o p - t u r n ) i n which sepa-

r a t i o n of f u n c t i o n has l e d t o s i g n i f i c a n t improvements i n per-

f ormance . Another a l t e r n a t i v e arrangement invo lv ing s e p a r a t i o n of

f u n c t i o n and f o u r r e d lamps was n o t e v a l u a t e d i n t h e s e t e s t s .

Such an arrangement of l i g h t s could c o n s i s t of a f o u r lamp a r r a y

i n which t h e outermost lamps a c t a s presence l i g h t s and a l s o

g i v e t h e s t o p and t u r n s i g n a l . I n a d d i t i o n , a second p a i r of

lamps provide t u r n and s t o p s i g n a l s . I n such an arrangement ,

t h e r e f o r e , two lamps would be shown a t n i g h t f o r t h e presence

l i g h t s . When a t u r n s i g n a l i s g iven both lamps on t h e t u r n s i d e

f l a s h a t h igh i n t e n s i t y . When a s t o p s i g n a l i s given a l l f o u r

lamps on t h e v e h i c l e a r e lit a t h igh i n t e n s i t y . I n such a sys-

tem two l i g h t s seen a t n i g h t would i n d i c a t e presence l i g h t s

whi le t h e appearance of f o u r l i g h t s , a t h igh i n t e n s i t y , would

i n d i c a t e t h e s t o p s i g n a l , t h u s g i v i n g t h e s t o p s i g n a l number

coding b u t n o t complete f u n c t i o n a l s e p a r a t i o n . I n an unpublished

s tudy such a system was found t o be more e f f e c t i v e than t h e

p r e s e n t concept and had t h e advantage of r e l i a b i l i t y f o r t h e

s i g n a l l i g h t s which u t i l i z e two lamps on each s i d e and w i l l ,

t h e r e f o r e , remain o p e r a t i v e i f one of t h e s e lamps f a i l s . How-

e v e r , t h e system was no more e f f e c t i v e , i n terms of d r i v e r

r e a c t i o n t ime , t han a system i n which f o u r lamps a r e used , t h e

o u t e r ones be ing o n l y p re sence l i g h t s and t h e o t h e r two lamps

g i v i n g on ly t h e s t o p and t u r n s i g n a l s , The l a t t e r arrangement

would be p r e f e r r e d because it p rov ides redundancy i n coding .

A s t o p s i g n a l can be d i s c e r n e d by f o u r lamps, and by t h e d i f -

f e r e n c e i n i n t e n s i t y between t h e s t o p lamps and p re sence lamps.

I n t h e s t u d y concerned w i t h t h e e f f e c t s of a low dose of

a l c o h o l no s i g n i f i c a n t e f f e c t upon d r i v e r r e a c t i o n t ime t o s i g -

n a l s was found. Other s t u d i e s have shown t h a t , f o r t h e a l c o h o l

l e v e l s t h a t were reached by t h e t e s t s u b j e c t s , r e d u c t i o n s occur-

r e d i n v i s u a l and motor a s p e c t s of n i g h t d r i v i n g (Ca rpen te r ,

1 9 5 9 ; Mortimer, 1 9 6 3 ) . While it i s p o s s i b l e t h a t h i g h e r a l c o h o l

dosages would have produced i n c r e a s e s i n r e a c t i o n t ime , t h e

s i g n i f i c a n t l y l onge r r e a c t i o n t imes i n system 1 compared t o

system 8 c o r r o b o r a t e d t h e f i n d i n g s of t h e p rev ious t es t s . The

r e s u l t s cou ld , t h e r e f o r e , be i n t e r p r e t e d t o i n d i c a t e t h a t d i f -

f e r e n c e s i n t h e coding concep t s had a s i g n i f i c a n t e f f e c t upon

d r i v e r performance which could n o t b e o b t a i n e d by a l c o h o l l e v e l s

of approximate ly 0 . 0 6 p e r c e n t . Although a l c o h o l i s well known

t o be s i g n i f i c a n t l y i nvo lved i n f a t a l a c c i d e n t s and t o a f f e c t

human a b i l i t i e s d e t r i m e n t a l l y , it was found t h a t t h e s i g n a l

system u s i n g f u n c t i o n a l s e p a r a t i o n and c o l o r coding produced

d i f f e r e n c e s i n d r i v e r performance, whereas a l c o h o l d i d n o t .

Th i s cou ld be i n t e r p r e t e d t o mean t h a t d i f f e r e n c e s i n s i g n a l

system d e s i g n can p rov ide changes i n d r i v e r performance g r e a t e r

t han t h o s e t h a t a c c r u e from moderate a l c o h o l l e v e l s , and would

s u g g e s t a s t r o n g s a f e t y advantage of t h e i n c o r p o r a t i o n of con-

c e p t s found i n some of t h e expe r imen ta l systems a s compared

t o t h e p r e s e n t system coding.

The coding concepts t h a t were eva lua ted i n t h e s e tests a r e

n o t t h e only means by which s i g n a l s may be presented . I t has

a l r e a d y been s t a t e d elsewhere (Mortimer, 1966; Nickerson e t a l , ,

1968) t h a t s i g n a l s may be coded by t h e shape of lamps o r by

lamp a r e a , a l though it was f e l t t h a t t h e s e a r e n o t very power-

f u l cues s i n c e they w i l l be d i f f i c u l t t o pe rce ive a t t h e d i s -

t ances involved i n d r i v i n g . S i g n a l s may a l s o be coded by vary-

i n g t h e f l a s h r a t e o r by p u l s a t i n g t h e l i g h t s , e t c . For example,

t h e r e i s a v a i l a b l e an a f t e rmarke t k i t which i s in tended t o pro-

duce a r e l a t i v e l y high frequency p u l s a t i o n of about 9 cps when-

e v e r s t o p l i g h t s a r e a p p l i e d ( S a f e t y Systems, I n c . , 1969) .

The use of some o t h e r codes n o t i n v e s t i g a t e d i n t h e s e t e s t s ,

such a s high f l a s h r a t e s , would probably improve t h e d e t e c t i o n

of s t o p s i g n a l s given by t h e p r e s e n t system which u t i l i z e s no

p e r c e p t u a l redundancy and a fundamental ly weak psychologica l

coding technique . This i s n o t l i k e l y t o be t r u e of t h e exper i -

mental systems, because they use powerful coding methods, However,

a d d i t i o n a l coding i s n o t n e c e s s a r i l y excluded by those t h a t a r e

recommended.

I t would probably be more s a t i s f a c t o r y t o sugges t t h a t addi-

t i o n a l codes be used a s needed i f subsequent r e sea rch i n d i c a t e s

t h a t new types of s i g n a l s should be t r a n s m i t t e d by r e a r l i g h t -

i n g systems e i t h e r i n a d d i t i o n t o o r i n s t e a d of those t h a t a r e

now presented . Such s i g n a l s w i l l r e q u i r e s p e c i f i c coding methods

i n o r d e r t o provide i d e n t i f i c a t i o n f o r them and t o avoid confu-

s i o n wi th s i g n a l s now presen ted . I n t h i s r e s p e c t va r ious v e h i c l e

s i g n a l s have been sugges ted o r a r e a v a i l a b l e a s a f t e rmarke t k i t s

such a s t h e fo l lowing: a q u a n t i t a t i v e i n d i c a t i o n of d e c e l e r a t i o n

r a t e by f l a s h i n g t h e s t o p l i g h t s a t a r a t e which v a r i e s wi th t h e

l e v e l of d e c e l e r a t i o n (Vovoedsky, 1965) ; f l a s h i n g of t h e s t o p

l i g h t s t o i n d i c a t e d e c e l e r a t i o n l e v e l s above about 0.3g (Pana-

S top , 1 9 6 9 ) ; p u l s a t i n g s t o p l i g h t s (Sa fe ty Systems, I n c . , 1969) ;

a s i g n a l g iven when t h e v e h i c l e i s a c c e l e r a t i n g o r d e c e l e r a t i n g

a c t i v a t e d by t h e l e v e l of a c c e l e r a t i o n o r d e c e l e r a t i o n (Kle in ,

1969) ; a combinat ion lamp which p rov ides a con t inuous ly burn ing

w h i t e running l i g h t t o t h e f r o n t and r e d t o t h e r e a r , amber

f r o n t and r e d r e a r t u r n s i g n a l s and amber forward and r e d r e a r

s t o p l i g h t s l o c a t e d on t h e v e h i c l e roof (Speedway S a f e t y Devices

Company, 1 9 6 9 ) ; an amber s i g n a l when t h e a c c e l e r a t o r peda l has

been r e l e a s e d (Triex-D L i g h t , 1 9 6 6 ) ; high-mounted s t o p l i g h t s ,

a v a i l a b l e a s an o p t i o n a l e x t r a on t h e Ford Thunderbird ( W a l l s t r e e t

J o u r n a l , 1969) ; a lane-change s i g n a l (Hess, 1967) ; a pan ic - s top

s i g n a l (Quick S top L igh t Company, 1968) ; a p roposa l by Hendrickson

(1969) t o use a green s i g n a l f o r dep res sed a c c e l e r a t o r , amber f o r

c o a s t i n g , and red when t h e b rakes a r e a p p l i e d ; a forward f a c i n g

s t o p s i g n a l marketed by Disco Research, I n c , (1969) ; and a modi-

f i e d v e r s i o n of a c o a s t i n g s i g n a l i n which t h e s t o p s i g n a l au to -

m a t i c a l l y appears a s soon a s t h e a c c e l e r a t o r peda l i s f u l l y

r e l e a s e d on t h o s e occas ions when t h e a c c e l e r a t o r i s r e l e a s e d

h u r r i e d l y (McNiel, 1969) . The v a l u e of some of t h e s u g g e s t i o n s ,

which i n c l u d e s i g n a l s t h a t do n o t appear on c u r r e n t v e h i c l e s ,

ha s been d i s c u s s e d e l sewhere (Mortimer, 1967; Nickerson e t a l . ,

1968) . The s t u d i e s t h a t have been completed i n t h i s program have

r e i n f o r c e d most of t h e r e s u l t s found i n p rev ious analogous e x p e r i -

ments (Mortimer, 1969a; 1969b) and have ex tended t h o s e f i n d i n g s .

On t h e b a s i s of t h e s e s t u d i e s it could be concluded t h a t number

coding, s p e c i f i c t y p e s of f u n c t i o n a l s e p a r a t i o n between lamps,

and c o l o r coding r e s u l t i n improvements i n d r i v e r performance

measurements. I n a d d i t i o n , it has been found t h a t t h e use o f

h igh p re sence - s igna l l i g h t i n t e n s i t y r a t i o s , wh i l e improving

d r i v e r performance p a r t i c u l a r l y when combined w i t h h igh o v e r a l l

i n t e n s i t i e s of t h e s i g n a l s , does n o t d imin i sh t h e e f f e c t i v e n e s s

of number coding , f u n c t i o n a l s e p a r a t i o n , o r c o l o r coding ,

The r e s e a r c h c a r r i e d o u t up t o now has f i r m l y e s t a b l i s h e d

t h a t f u n c t i o n a l s e p a r a t i o n of lamps i s a most e f f e c t i v e t ech-

n ique and should be recommended f o r use. I t has been shown t h a t ,

f o r p a r t i a l s e p a r a t i o n of f u n c t i o n , t h e presence and t u r n s i g n a l

should be combined i n one lamp and s e p a r a t e d from t h e s t o p lamp.

There a r e r easons why t h i s form of f u n c t i o n a l s e p a r a t i o n would

be recommended on a s t r i c t l y a n a l y t i c a l b a s i s . The importance

of t h e s t o p s i g n a l f o r highway s a f e t y sugges t s t h a t t h i s s i g n a l

should be given a s p e c i f i c code. However, t u r n s i g n a l s p r e s e n t l y

use two coding t echn iques by which they a r e i d e n t i f i e d , namely

f l a s h i n g and an i n c r e a s e i n i n t e n s i t y . Therefore , t h e t u r n s i g -

n a l i s redundant ly coded and, because it i s of secondary impor-

t ance t o t h e s t o p s i g n a l , could be combined wi th t h e presence

l i g h t . This would be t h e recommended coding technique f o r a

r e a r l i g h t i n g system wi th p a r t i a l f u n c t i o n a l s e p a r a t i o n a s was

shown by r e s u l t s (Mortimer, 1969b) i n t h e tu rn - s top and s top-

t u r n modes i n which t h e system employing presence- turn s i g n a l i n

combination was s u p e r i o r t o t h e system i n which t h e presence

l i g h t was s e p a r a t e d from t h e tu rn - s top s i g n a l .

The d a t a show t h a t , f o r a system employing a s i n g l e c o l o r

( r e d ) , e f f e c t i v e n e s s i s improved when complete f u n c t i o n a l separa-

t i o n between p resence , t u r n and s t o p s i g n a l s a r e employed, I t

should be no ted t h a t t h i s improvement was found i n t e s t s conduc-

t e d under n i g h t d r i v i n g c o n d i t i o n s i n which t h e presence l i g h t

obv ious ly p l a y s an impor tan t r o l e . I n daytime c o n d i t i o n s a par-

t i a l l y s e p a r a t e d system i n which t h e presence and t u r n s i g n a l s

a r e combined i n one lamp s e p a r a t e d from t h e lamp g i v i n g t h e s t o p

s i g n a l would provide adequate coding. This i s because i n t h e

daytime such p a r t i a l s e p a r a t i o n would i n e f f e c t be complete sepa-

r a t i o n between t h e t u r n and t h e s t o p s i g n a l whenever h e a d l i g h t s

and, hence presence l i g h t s , were n o t i n use . The argument f o r a

completely f u n c t i o n a l l y s e p a r a t e d r e a r l i g h t i n g system i n which

s e p a r a t e lamps a r e used f o r p resence , t u r n and s t o p s i g n a l s i s

q u i t e s t r o n g according t o t h e n i g h t t i m e d a t a .

I t was a l s o found t h a t when c o l o r coding i s in t roduced i n

t h e form of green-blue presence l i g h t s and r e d s t o p s i g n a l s , f o r

systems employing p a r t i a l s e p a r a t i o n of f u n c t i o n t h e t u r n s i g n a l

should a g a i n be coded on t h e presence lamp. This would mean t h a t

t h e t u r n s i g n a l would be t h e same c o l o r a s t h e presence lamp.

There would n o t appear t o be any p a r t i c u l a r problem w i t h such a

p r o p o s i t i o n . I t should be no ted t h a t such p a r t i a l f u n c t i o n a l

s e p a r a t i o n us ing green-blue presence and t u r n s i g n a l s would pro-

v i d e an a d d i t i o n a l code t o i d e n t i f y t h e impor tan t s t o p s i g n a l

more r e a d i l y t han i n an analogous a l l - r e d system, I n such a

green-blue and r e d system t h e s t o p s i g n a l would be t h e on ly r e d

s i g n a l , which would a i d i n i t s i d e n t i f i c a t i o n and d e t e c t i o n over

and above t h e e f f e c t i v e n e s s provided by f u n c t i o n a l s e p a r a t i o n .

There would seem t o be l i t t l e doubt t h a t i n t h e long run such

r e a r l i g h t i n g system coding would be h i g h l y e f f e c t i v e and should

reduce rear-end c o l l i s i o n s .

The d a t a have a l s o shown t h a t t h e u se of complete func-

t i o n a l s e p a r a t i o n and c o l o r coding r e s u l t s i n s t i l l f u r t h e r

improvements. Data from an e a r l i e r s tudy (Mortimer, 1969b) have

shown t h a t t h e use of green-blue presence l i g h t s s e p a r a t e d from

r e d t u r n s i g n a l s i n s e p a r a t e lamps from r e d s t o p s i g n a l s r e s u l -

t e d i n a d d i t i o n a l improvement i n d r i v e r performance. O v e r a l l ,

however, t h e g r e a t e s t improvements were found w i t h a system which

employed complete f u n c t i o n a l s e p a r a t i o n and c o l o r coding f o r each

of t h e s e t h r e e s i g n a l s i n which presence l i g h t s were green-b lue ,

t u r n s i g n a l s were amber, and s t o p s i g n a l s were r ed . The s t u d i e s

c a r r i e d o u t i n t h i s program have a l s o c o n s i s t e n t l y found such a

system t o be s u p e r i o r t o t h e o t h e r s .

There a r e numerous r a m i f i c a t i o n s t o t h e u se of complete

f u n c t i o n a l s e p a r a t i o n and complete c o l o r coding f o r each lamp

i n terms of f a c t o r s such a s c o s t and r e l i a b i l i t y of o p e r a t i o n .

I n a d d i t i o n , t h e r e a r e s t i l l q u e s t i o n s t h a t need t o be answered

concern ing t h e use of green-blue a s p a r t of a v e h i c l e r e a r l i g h t -

i n g system. However, s t u d i e s have shown t h a t t h e r e i s l i t t l e

d i f f e r e n c e i n i d e n t i f i c a t i o n d i s t a n c e and r e c o g n i t i o n d i s t a n c e

of green-blue and r e d l i g h t s and t h a t they p e n e t r a t e water vapor

fog about e q u a l l y w e l l (Middleton, 1963; Mortimer, 1969a) . Other

types of atmospheric e f f e c t s , such a s haze, a r e n o t a s w e l l

s t u d i e d and may d i f f e r e n t i a l l y a f f e c t t h e t ransmiss ion of blue-

green compared t o r ed . However, i t i s g e n e r a l l y concluded t h a t

t h e r e s o l u t i o n of problems a s s o c i a t e d wi th atmospheric s p e c t r a l

t r ansmiss ion w i l l n o t be s i g n i f i c a n t l y a f f e c t e d by t h e wavelengths

employed. The more impor tant c o n s i d e r a t i o n s a r e those assoc ia -

t e d wi th t h e i d e n t i f i c a t i o n and recogn i t ion of such c o l o r s by

i n d i v i d u a l s wi th both normal and c o l o r v i s i o n , Atmospheric degra-

d a t i o n e f f e c t s of t h e apparent i n t e n s i t y of t h e c o l o r s can only

be adequate ly overcome by t h e use of high i n t e n s i t i e s (Middleton,

1963) . Problems a s s o c i a t e d wi th c o s t , r e l i a b i l i t y and t h e

d e s i r a b i l i t y of r e t r o f i t t i n g e x i s t i n g v e h i c l e s w i l l n o t be d i s -

cussed h e r e a t l eng th s i n c e they a r e beyond t h e scope of t h i s

r e s e a r c h program. The p o s s i b i l i t i e s a s s o c i a t e d w i t h r e t r o f i t -

t i n g e x i s t i n g v e h i c l e s has a l r e a d y been d i scussed elsewhere

(Systems A s s o c i a t e s , I n c . , 1968) .

I n s o f a r a s r e l i a b i l i t y i s concerned t h e r e a r e c e r t a i n advan-

t a g e s t o t h e use of s e p a r a t e lamps c a r r y i n g o u t d i f f e r e n t func-

t i o n s , p a r t i c u l a r l y when coupled wi th complete c o l o r coding a s

would be t h e l o g i c a l recommendation from t h e s e s t u d i e s . P r e s e n t

r e a r l i g h t i n g systems which employ multi-compartment lamps w i t h

s e p a r a t e bu lbs i n each compartment have a b u i l t - i n redundant

f e a t u r e which i n c r e a s e s t h e o p e r a t i o n a l r e l i a b i l i t y of t h e sys-

tem, I n t h e e v e n t t h a t one of t h e bulbs i n a compartment should

be burned o u t t h e bu lb i n ano the r compartment of t h e same lamp

w i l l s t i l l be capable of g iv ing t h e s i g n a l . However, many cur-

r e n t v e h i c l e s do n o t u t i l i z e t h i s form of redundancy because

they only have one lamp on each s i d e . I n a d d i t i o n , it i s p o s s i b l e

t h a t t h e p r e s e n t system can g ive f a l s e s i g n a l s when a system f a i l -

u r e has occu r red , For example, i f a f r o n t t u r n s i g n a l bu lb

f a i l s t h e use of t h e t u r n i n d i c a t o r r e s u l t s i n a s teady-burning

r e a r l i g h t which i s i n d i s t i n g u i s h a b l e from t h e s i g n a l given by

one s t o p lamp. A fo l lowing d r i v e r , t h e r e f o r e , would n o t know

whether a t u r n s i g n a l i s be ing g iven on t h e s i d e i n which a

s teady-burning l i g h t h a s appeared o r whether a s t o p s i g n a l i s

be ing shown when t h e lamps on t h e o t h e r s i d e of t h e v e h i c l e a r e

mal func t ion ing . Thus, ambiguity i n i n t e r p r e t a t i o n of s i g n a l s

by fo l lowing d r i v e r s can occur w i t h t h e c u r r e n t system i n s p i t e

of c e r t a i n f e a t u r e s which do a f f o r d it p o t e n t i a l r e l i a b i l i t y

through lamp redundancy.

I n t h e same s i t u a t i o n a system which uses green-blue p re s -

ence , amber t u r n and r e d s t o p lamps would show a s teady-burn ing

amber l i g h t on t h e r e a r of t h e v e h i c l e . The on ly l o s s i n code

i n t h i s s i t u a t i o n would be t h a t t h e l i g h t i s n o t f l a s h i n g , b u t

t h e c o l o r coding a lone would enab le a fo l lowing d r i v e r t o r e a d i l y

i d e n t i f y a t u r n s i g n a l and, because s t o p s i g n a l s a r e coded r e d ,

could n o t confuse i t w i t h a s t o p s i g n a l . I n a d d i t i o n , i f a s i n g l e

s t o p bu lb had b u r n t o u t t h e appearance of r e d i n t h e remaining

lamp would s t i l l s i g n a l a s t o p i n such a system. The re fo re , t h e r e

i s a l s o r e l i a b i l i t y i n t h e use of s e p a r a t i o n of f u n c t i o n wi th

c o l o r coding i n s p i t e of t h e f a c t t h a t t h i s may r e s u l t i n a reduc-

t i o n of t h e k ind of b u i l t - i n redundancy t h a t can on ly be achieved

by t h e use of a d d i t i o n a l f i l a m e n t s .

Perhaps t h e most impor t an t c o n s i d e r a t i o n t h a t may a f f e c t

t h e choice of a change i n t h e v e h i c l e r e a r l i g h t i n g system should

be t h e p o t e n t i a l f u t u r e developments i n r e a r l i g h t i n g which may

t a k e p l a c e . I t i s envisaged t h a t , fo l lowing a d d i t i o n a l r e s e a r c h ,

d i f f e r e n t t ypes of i n fo rma t ion may be found most d e s i r a b l e t o

d i s p l a y t o fo l lowing v e h i c l e s v i a t h e r e a r l i g h t i n g and s i g n a l -

i n g system. For example, it may be found e s s e n t i a l t o code

v e l o c i t y on a cont inuous o r a d i s c r e t e b a s i s . I t w i l l then be

neces sa ry t o de te rmine an e f f e c t i v e means t o provide such speed

coding. I t would be unfor tunate i f a p r i o r s e l e c t i o n of coding

techniques would no t al low t h e same o r o t h e r e f f e c t i v e means t o

be used i n a compatible way f o r speed coding.

With t h e s e types of cons ide ra t ions borne i n mind a h i e r -

archy of coding techniques f o r r e a r l i g h t i n g systems can be

def ined wi th t h e f i n a l choice being made on t h e b a s i s of prac-

t i c a l i t y , c o s t , p r e s e n t and f u t u r e compat ib i l i ty and, perhaps,

r e g u l a t i o n s i n o t h e r c o u n t r i e s .

There appears t o be no doubt t h a t f u n c t i o n a l separa t ion of

t h e s t o p s i g n a l from o t h e r veh ic le s i g n a l s should be accomplished.

A second s t e p would be t o completely s e p a r a t e presence, t u r n and

s t o p lamps from each o t h e r r e t a i n i n g red f o r a l l t h r e e func t ions .

A t h i r d s t e p , which was n o t s p e c i f i c a l l y i n v e s t i g a t e d a s an

o v e r a l l system i n t h e s e s t u d i e s , would be t o employ complete

f u n c t i o n a l s e p a r a t i o n of red presence l i g h t s , amber t u r n s i g n a l s

and red s t o p lamps. I t should be noted t h a t any of these t h r e e

s t e p s would be e n t i r e l y synonymous w i t h p resen t r e a r l i g h t i n g

systems t h a t a r e now found on v e h i c l e s e i t h e r i n t h e U.S. o r i n

o t h e r p a r t s of t h e world. European p r a c t i c e has employed amber

f o r t h e t u r n s i g n a l f o r a number of yea r s and t h i s i s permit ted

i n most s t a t e s of t h e U.S. I t would provide b e n e f i t s both i n

terms of d r i v e r performance and of r e l i a b i l i t y i n a f f e c t i n g

s i g n a l i d e n t i f i c a t i o n i n the even t of a malfunct ion, a s a l ready

descr ibed.

A f o u r t h s t e p which i n c r e a s e s t h e e f f e c t i v e n e s s of func-

t i o n a l s e p a r a t i o n of t h e s t o p s i g n a l would be t o employ green-

b l u e (whose wavelength c h a r a c t e r i s t i c s s t i l l need t o be d e t e r -

mined t o provide proper cueing f o r normal and color-b l ind d r i v e r s )

f o r t h e presence s i g n a l land the t u r n s i g n a l combined i n t h e same

lamps, with red s t o p s i g n a l s i n s e p a r a t e lamps. F i n a l l y , more

e f f e c t i v e than these would be t h e use of green-blue f o r presence

lamps, amber f o r t u r n lamps, and red f o r s t o p lamps. I t would

appear t h a t most ob jec t ions t o t h e use of such a system can be

h he r e a r s i d e marker l i q - h t must be t h e same c o l o r a s t h e presence l i g h t ,

r e a d i l y overcome i f t h e presumed a d d i t i o n a l c o s t of t h e s i x lamps

i s cons idered t o be warran ted ,

Attached t o t h e recommendation f o r a complete f u n c t i o n a l l y

sepa ra t ed system employing c o l o r coding f o r a l l t h r e e s i g n a l s i s

t h e r i d e r t h a t t h e green-blue presence l i g h t s remain l i g h t e d con-

t i n u o u s l y when t h e h e a d l i g h t s a r e i n use . This means t h a t t h e

presence l i g h t s should n o t be tu rned o f f , f o r example, when s t o p

s i g n a l s a r e g iven . I n t h i s way d r i v e r s would o b t a i n t h e maxi-

mum advantage of a new system whi le o l d e r v e h i c l e s w i th t h e

p r e s e n t a l l - r e d system a r e s t i l l on t h e road. The q u e s t i o n of

t h e c o m p a t i b i l i t y of green-blue presence l i g h t s wi th o t h e r vehi -

cles showing t h e c u r r e n t r e d presence l i g h t s cannot be adequate ly

answered a t t h i s time. However, a n a l y s i s of t h e s i t u a t i o n would

i n d i c a t e t h a t l i t t l e confus ion should a r i s e s i n c e presence l i g h t s

have t h e f u n c t i o n of marking a v e h i c l e and t h i s f u n c t i o n should

be independent of t h e hue. I t would be d i f f i c u l t t o s t r u c t u r e

an exper imenta l s i t u a t i o n t o i n v e s t i a g a t e t h i s phenomenon. I t

has been sugges ted t h a t t h e on ly way t o de te rmine c o m p a t i b i l i t y

of two d i f f e r e n t r e a r l i g h t i n g systems would be t o equip v e h i c l e s

i n a r e g i o n wi th o l d and new systems and t o e v a l u a t e d r i v e r reac-

t i o n s and a c c i d e n t s t a t i s t i c s . Some mixing of v e h i c l e s w i t h r e d

and green-blue presence l i g h t s was done a t t h e General Motors

Proving Ground i n Milford wi th no s e r i o u s drawbacks r e p o r t e d by

t h e t e s t d r i v e r s (Sage, 1 9 6 7 ) . PRESENCE LAMP ARRAY. The r e s u l t s of t h i s r e s e a r c h program

have a l s o sugges ted t h a t t h e arrangement of presence l i g h t s can have

an e f f e c t upon t h e a b i l i t y wi th which d r i v e r s d e t e c t c l o s u r e w i t h

another v e h i c l e . The s imula t ion s t u d i e s showed t h a t t h e s i z e of t h e

presence l i g h t s l o c a t e d i n a h o r i z o n t a l p l ane had l i t t l e e f f e c t

upon t h e d e t e c t i o n of a change i n headway. Thus, lamps which were

small sou rces a t t h e edges of t h e s imula ted v e h i c l e d i d n o t provide

any improved d r i v e r performance over lamps which extended e i t h e r

p a r t i a l l y o r completely a c r o s s t h e f u l l width. This means t h a t

t h e f a c t t h a t c u r r e n t p r a c t i c e invo lves t h e use of presence

l i g h t s of v a r i o u s a r e a s does n o t d e t r i m e n t a l l y a f f e c t t h e de tec-

t i o n of r e l a t i v e v e l o c i t i e s between two v e h i c l e s a t n i g h t , The

f i n d i n g s c o n s i s t e n t l y i n d i c a t e d t h a t t h e use of a lamp a r r a y i n

which l i g h t s were mounted a t t h e f o u r co rners of a square would

improve t h e s e n s i t i v i t y of t h e obse rve r i n d e t e c t i n g a change i n

p o s i t i o n of t h e l i g h t s . This f i n d i n g was t r u e whether t h e l i g h t s

were r e d o r green-blue. The subsequent experiment conducted on

t h e highway wi th t h e use of v e h i c l e s i n a car - fo l lowing s i t u a t i o n

l a r g e l y confirmed t h e s imula t ion s t u d i e s . I n t h a t s i t u a t i o n it

was found t h a t t h e l o c a t i o n of two l i g h t s j u s t above t h e C - p i l l a r s

of t h e t e s t v e h i c l e i n a d d i t i o n t o two l i g h t s l o c a t e d a t each

edge of t h e v e h i c l e above t h e r e a r bumper r e s u l t e d i n improved

d e t e c t i o n of c o a s t i n g compared t o t h e use of t h e two lamps i n

t h e lower l o c a t i o n a lone . The r e s u l t s bea r o u t t h e hypothes is

t h a t , because d r i v e r s must r e l y upon t h e angu la r subtense of

v e h i c l e presence l i g h t s a t n i g h t and t h e change i n t h i s angle

t o d e t e c t headway changes, t h e use of lamps mounted i n such a

way a s t o i n c r e a s e t h e o v e r a l l angle would i n c r e a s e t h e d r i v e r ' s

s e n s i t i v i t y . The r e s u l t s shown i n Table 6.13 show t h a t t h i s was

found.

On t h e b a s i s of t h e s e f i n d i n g s it would be recommended t h a t ,

i n a d d i t i o n t o t h e changes t h a t a r e suggested concerned wi th

s i g n a l l i g h t coding, a p a i r of presence lamps should be l o c a t e d

a t t h e upper edge of t h e v e h i c l e C - p i l l a r t o augment presence

lamps l o c a t e d n e a r t h e r e a r bumper. The use of high-mounted

presence l i g h t s has some o t h e r a t t e n d a n t advantages. One of

t h e s e i s t h a t i n such a l o c a t i o n t h e lamps should remain c l e a n e r ,

s i n c e less d i r t thrown up from t h e road would h i t them than con-

v e n t i o n a l l y mounted s i g n a l lamps, V i s i b i l i t y of v e h i c l e s would

a l s o be improved a t h i l l crests. High-mounted presence l i g h t s

may a l s o be v i s i b l e t o v e h i c l e s behind t h e fo l lowing v e h i c l e

and provide l o c a t i o n and change i n headway informat ion . This k ind

of in fo rma t ion could p o t e n t i a l l y be h e l p f u l t o d r i v e r s of c a r s

i n a s t r eam of t r a f f i c by provid ing e a r l i e r informat ion of

a c t u a l d e c e l e r a t i o n ( o r a c c e l e r a t i o n ) of v e h i c l e s t h a t may n o t

o the rwise be c l e a r l y v i s i b l e a t n i g h t and h e l p t o s t a b i l i z e

t r a f f i c flow. While t h e fo rego ing may sugges t t h a t t h e high-

mounted presence l i g h t s should a l s o a c t a s s t o p lamps t h i s i s

n o t t h e c a s e because of t h e d i f f e r e n t types of in fo rma t ion t h a t

s t o p lamps and presence l i g h t s provide . There a r e some poten-

t i a l d i sadvan tages t o t h e use of s t o p s i g n a l s seen through i n t e r -

vening c a r s which may d i s r u p t smooth t r a f f i c flow and c r e a t e

rear -end a c c i d e n t s (Mortimer, 1967) . Turn s i g n a l s could be com-

b ined w i t h high-mounted presence l i g h t s .

SIDE-MOUNTED TURN SIGNAL. The q u e s t i o n of t h e v i s i b i l i t y

of t h e t u r n s i g n a l was i n v e s t i g a t e d i n terms of t h e s p e c i f i c

s i t u a t i o n s i n which such a s i g n a l may be used and i n which it

can provide v a l u a b l e informat ion t o d r i v e r s and p e d e s t r i a n s

(Oyler , Dumville and Murphy, 1968) . The v i s i b i l i t y requi rements

of t h e t u r n s i g n a l a r e d i f f e r e n t from those of t h e s t o p s i g n a l ,

The a n a l y s i s showed t h a t t u r n s i g n a l s l o c a t e d i n t h e r e a r of a

v e h i c l e a r e f r e q u e n t l y i n v i s i b l e t o ano the r d r i v e r . I t was

cons idered necessa ry t o improve t h e h o r i z o n t a l f i e l d of v i s i -

b i l i t y of such a s i g n a l , This can be accomplished by mounting

a r e p e a t e r t u r n s i g n a l lamp a s f a r forward on t h e v e h i c l e a s

p o s s i b l e . I n a d d i t i o n , an experiment showed t h a t females i n t h e

lower percentage of s i t t i n g h e i g h t , which a f f e c t s t h e i r eye pos i -

t i o n , r e q u i r e d t h e r e p e a t e r s i g n a l t o be mounted a t n o t l e s s than

about 33 inches . To ensure v i s i b i l i t y of t h e s i g n a l f o r t h e

t a l l e r d r i v e r maximum mounting h e i g h t should n o t be more than 48

inches . The photometr ic requi rements f o r such a s i g n a l were then

e v a l u a t e d i n a s e r i e s of s u b j e c t i v e day, dusk, and n igh t t ime t e s t s

i n v a r i o u s angu la r l o c a t i o n s t o i n s u r e adequate v i s i b i l i t y under

daytime c o n d i t i o n s and comfor tab le i n t e n s i t i e s a t n i g h t . The

p r e s e n t SAE i n t e n s i t y recommendations f o r a side-mounted t u r n

s i g n a l were c l o s e t o t h e va lues found i n t h e s e tests f o r a

s i n g l e i n t e n s i t y l e v e l system. However, t h e d a t a c l e a r l y

showed t h e d e s i r a b i l i t y of us ing a d u a l i n t e n s i t y l e v e l , modu-

l a t e d through t h e h e a d l i g h t swi tch , t o provide g r e a t e r i n t e n -

s i t i e s f o r daytime v i s i b i l i t y and reduced i n t e n s i t i e s a t n i g h t

t o o f f - s e t t h e e f f e c t s of g l a r e . Some European v e h i c l e s a l r eady

u t i l i z e r e p e a t e r t u r n s i g n a l s b u t , i n g e n e r a l , t h e i r i n t e n s i t i e s

a r e cons ide rab ly below those t h a t were recommended by t h e s t u d i e s

conducted i n t h i s program a s w e l l a s t h o s e recommended i n SAE

J-914. Although it i s d i f f i c u l t t o show a r e l a t i o n s h i p between

t h e implementation of side-mounted t u r n s i g n a l s and a c c i d e n t

r e d u c t i o n , t h e work c a r r i e d o u t demonstrated t h a t s i t u a t i o n s

e x i s t e d i n which such a s i g n a l should be v i s i b l e t o o t h e r d r i v e r s

and t h a t t h i s cannot be a t t a i n e d by a rearward mounting a lone .

This argument appears s u f f i c i e n t t o j u s t i f y t h e d e s i r a b i l i t y of

side-mounted r e p e a t e r t u r n s i g n a l s , b u t obvious ly does n o t involve

t h e i m p l i c a t i o n s of t h e added c o s t t o t h e v e h i c l e . The d a t a t h a t

a r e p resen ted show t h e requirements f o r t h e mounting l o c a t i o n of

such a s i g n a l and t h e i n t e n s i t y requirements a s a func t ion of

lamp a r e a . I t was determined t h a t , i n accordance wi th p r e s e n t

SAE recommendations, and t o ensure c o m p a t i b i l i t y wi th t h e amber

forward f a c i n g t u r n s i g n a l and recommendations t h a t may be made

f o r an amber r e a r t u r n s i g n a l , t h e side-mounted s i g n a l should

a l s o be amber. Such a scheme u t i l i z e s t h e no t ion t h a t amber

s i g n a l s denote only one message, namely t h e i n t e n t i o n t o t u r n

o r change l a n e s .

DAY-NIGHT INTENSITY. A s u b s t a n t i a l e f f o r t i n t h i s r e sea rch

program was concerned wi th t h e development of i n t e n s i t y r equ i re -

ments f o r v e h i c l e r e a r s i g n a l lamps. This e f f o r t was conducted

i n o r d e r t o o b t a i n more informat ion than i s c u r r e n t l y a v a i l a b l e

t o show t h e a f f e c t of lamp a r e a and v a r i o u s c o l o r s . The whole

q u e s t i o n of s p e c i f i c a t i o n s concerning i n t e n s i t y requirements needs

a c a r e f u l review, s i n c e c u r r e n t p r a c t i c e i s t o write them ' in terms

of candlepower v a l u e s a lone . I t has been sugges ted b e f o r e

(Forbes , 1966) t h a t t h i s i s n o t a p p r o p r i a t e . The r e s u l t s of ou r

tes ts conf i rm t h a t candlepower i s n o t a s a t i s f a c t o r y means by

which t o s p e c i f y t h e i n t e n s i t y requi rements of automotive lamps,

This i s because t h e s u b j e c t i v e e f f e c t i v e n e s s of automotive s i g -

n a l lamps i s determined n o t on ly by candlepower b u t a l s o on t h e

b a s i s of luminous a r e a and t h e viewing d i s t a n c e ,

There i s an i n d i c a t i o n i n t h e d a t a t h a t daytime b r i g h t n e s s

e v a l u a t i o n s , which were made a t 75 and 270 f e e t , were n o t a f f e c -

t e d by t h e viewing d i s t a n c e , However, a t n i g h t , a t t h e same d i s -

t a n c e s , t h e r e was a d i f f e r e n t i a l e f f e c t i n terms of i n t o l e r a b l e

g l a r e due t o t h e d i s t a n c e , The d a t a a l s o showed t h a t n e i t h e r

day no r n i g h t t i m e c r i t e r i a could be exp la ined on t h e b a s i s of

candlepower a lone o r on t h e b a s i s of luminance v a l u e s a lone .

The problem of de te rmin ing t h e b a s i s upon which s u b j e c t i v e

e v a l u a t i o n s of t h e e f f e c t s of lamp i n t e n s i t y and a r e a a r e made

by human o b s e r v e r s has been d i s c u s s e d p r e v i o u s l y (Merr ik , 1968;

P r o j e c t o r e t a l . , 1969) and i s n o t s imple . However, t h i s does

n o t mean t h a t s u i t a b l e u se cannot be made of d a t a of t h e t ype

t h a t were g e n e r a t e d , This i s because c e r t a i n c o n d i t i o n s can be

t aken t h a t a r e p a r t i c u l a r l y r e l e v a n t t o d r i v i n g and t h e d a t a

a p p l i e d t o t hose s i t u a t i o n s . This was done i n t h e p r e s e n t i n s t a n c e ,

f o r example by s e l e c t i n g t h e 75-foot d a t a of i n t o l e r a b l e g l a r e

i n t e n s i t i e s r a t h e r t han t h e h i g h e r v a l u e s which were o b t a i n e d a t

270 f e e t .

I t was found t h a t d i f f e r e n t i a l i n t e n s i t y requi rements a r e

needed f o r d i f f e r e n t lamp c o l o r s . These have a l r e a d y been sug-

g e s t e d by t h e d a t a i n t h e SAE recommendations (SAE J-575C, 1966)

f o r r e d and amber s i g n a l lamps. Those d a t a a l s o show t h a t t h e r e

has been some p rev ious concern w i t h t h e i n f l u e n c e of lamp a r e a

a s shown by t h e minimum i n t e n s i t y requi rements of c l a s s A and

c l a s s B s i g n a l lamps. However, t h e SAE d a t a need t o be extended.

The r e s e a r c h t h a t h a s been completed has accomplished t h i s aim

by conduct ing t h e work f o r whi te , r e d , amber and green-blue

l i g h t s over a range of a r e a s from about 6 .0 t o 37.0 square

inches . The f i n d i n g s have been summarized i n t h e form of t a b l e s

and a l s o i n terms of a methodology by which t h e e f f e c t of a r e a

and c o l o r can be taken i n t o account i n o r d e r t o d e r i v e appro-

p r i a t e i n t e n s i t i e s f o r daytime v i s i b i l i t y and g l a r e e f f e c t s a t

n i g h t . The recommendations a r e shown f o r r e d , amber and green-

b l u e lamps a s a f u n c t i o n of luminous a r e a i n F igures 2.6-2,8.

These d a t a i n d i c a t e t h a t i n t e n s i t i e s which a r e s u i t a b l e f o r use

a t n i g h t w i l l be cons idered inadequa te under daytime cond i t ions .

The d a t a , i n d i c a t e minimum and maximum i n t e n s i t y l i m i t a t i o n s t h a t

a r e recommended a t n i g h t i n o r d e r t o provide adequate v i s i b i l i t y

of t h e s i g n a l wi thou t caus ing e x c e s s i v e g l a r e d i scomfor t and

d i s a b i l i t y . The daytime minimum v a l u e s were s e l e c t e d s o t h a t ,

d u r i n g dusk o r dawn, g l a r e d iscomfor t would a f f e c t n o t more than

25 p e r c e n t of d r i v e r s . The maximum day l e v e l s a r e those t h a t

w i l l never have t o be exceeded t o provide a h i g h l y v i s i b l e s i g -

n a l under b r i g h t day c o n d i t i o n s . I t w i l l be noted t h a t t h e day-

time range between minimum and maximum recommended va lues i s

q u i t e l a r g e , depending upon t h e lamp c o l o r . This i s due t o t h e

obvious f a c t t h a t daytime i l l u m i n a t i o n l e v e l s va ry g r e a t l y

d u r i n g t h e course of a day and s u g g e s t s t h a t what i s r e a l l y needed

i s an a d a p t i v e system t h a t a d j u s t s t h e s i g n a l l i g h t i n t e n s i t y t o

meet t h e changes i n t h e ambient i l l u m i n a t i o n . Nonetheless , t h e

minimum recommended daytime i n t e n s i t i e s a r e h i g h e r than t h o s e

now used. Hence, t h e use of l e v e l s w i t h i n t h e daytime range

w i l l produce an improvement i n t h e daytime v i s i b i l i t y of v e h i c l e

s i g n a l l i g h t s . The n igh t t ime range i s s m a l l e r than t h a t found

i n t h e day and i n no c a s e o v e r l a p s t h e daytime va lues . The d i s -

crepancy between t h e minimum daytime recommended v a l u e s and t h e

maximum n i g h t t i m e v a l u e s f o r a lamp of t h e same c o l o r and same

a r e a i s 100-200 cp. This means t h a t a d u a l - i n t e n s i t y system i s

r e q u i r e d i n which daytime and n i g h t t i m e i n t e n s i t i e s a r e made a v a i l -

a b l e . Such a concept i s n o t new and has been d i scussed f o r a

number of yea r s both i n t h i s country (AMA, 1954-1965) and i n

Europe where d u a l - i n t e n s i t y s t a n d a r d s have a l r e a d y been prepared

by t h e ECE (1967) and implemented i n some v e h i c l e s . I t w i l l be

noted t h a t t h e recommended v a l u e s a r e compatible wi th t h e European

and A u s t r a l i a n r e g u l a t i o n s . The i r minima and maxima a r e lower,

b u t t h e r e i s an o v e r l a p i n t h e i n t e n s i t y ranges .

I f t h e recommendations t h a t a r e shown i n t h i s r e p o r t i n

F igures 2.6-2.8 were t o be implemented, t h e a c t u a l d i f f e r e n c e

i n i n t e n s i t y between t h e maximum n igh t t ime and t h e minimum day-

time va lues t h a t a r e shown would have t o be g r e a t e r than t h e mini-

mum range, This i s because lamp manufacturers must des ign t o

p r a c t i c a l t o l e r a n c e s , and t h i s could only be ensured by them i f

they designed lamps whose maximum n igh t t ime i n t e n s i t i e s were

somewhat below t h o s e recommended and whose minimum daytime i n t e n -

s i t i es were somewhat above those recommended. I n p r a c t i c e , t h e r e -

f o r e , t h e d i f f e r e n c e between n i g h t and daytime i n t e n s i t i e s t h a t

would be found on v e h i c l e s would be l a r g e r than those shown a s

maximum n i g h t and minimum day v a l u e s , I f t h e mid- in tens i ty of

t h e day and n i g h t i n t e n s i t y range was used, approximately a 1 0 : l

day-night i n t e n s i t y r a t i o would r e s u l t a s recommended by Finch

(1968).

MANUAL INTENSITY SWITCHING, A d u a l - i n t e n s i t y system w i l l be

advantageous under normal day and n igh t t ime c o n d i t i o n s compared

t o a s i n g l e i n t e n s i t y system. I t was s t a t e d t h a t such a system,

dependent on t h e p o s i t i o n of t h e h e a d l i g h t swi tch , does n o t f u l l y

e x p l o i t i t s p o t e n t i a l under c o n d i t i o n s of degraded atmospheric

t r ansmiss ion . For t h i s reason i t was recommended t h a t a manual

i n t e n s i t y o v e r r i d e swi tch be used, The purpose of t h e o v e r r i d e

swi tch i s t o enab le t h e d r i v e r t o o b t a i n t h e h igh i n t e n s i t y , day-

t i m e s i g n a l s , i n c o n d i t i o n s i n which t h e h e a d l i g h t s a r e i n use .

This would occur i n daytime poor v i s i b i l i t y c o n d i t i o n s , such a s

i n snow o r fog and, s i m i l a r l y , a t n i g h t . I t was cons idered t h a t ,

because d r i v e r s may misuse t h e i n t e n s i t i e s e i t h e r i n t e n t i o n a l l y

o r u n i n t e n t i o n a l l y , f o r c e f u l feedback of t h e s t a t u s of t h e

swi tch must be g iven by c l e a r l a b e l i n g and swi tch p o s i t i o n

i n d i c a t i o n , It was a l s o shown t h a t t o g g l e , rocker and r o t a r y

swi tches have s u i t a b l e modes of o p e r a t i o n i n providing feedback

t o t h e d r i v e r which i s n o t t h e c a s e i n some o t h e r k inds of

swi tches , such a s push-pull t y p e s . I n a d d i t i o n , it was cons idered

u s e f u l t o i n c o r p o r a t e a feedback s i g n a l which would a l e r t t h e

d r i v e r t h a t he i s on t h e h igh i n t e n s i t y p o s i t i o n each time t h e

b rakes a r e opera ted .

There may be an i n i t i a l pe r iod of misuse of t h e i n t e n s i t y

o v e r r i d e swi tch . Subsequently, due t o reminders from fol lowing

d r i v e r s and by p r a c t i c e , misuse probably would become r a r e . T h i s

was n o t t e s t e d i n t h i s p r o j e c t , b u t t h e i n f e r e n c e i s made based

on t h e g e n e r a l l y a p p r o p r i a t e behavior of d r i v e r s i n dimming high-

beam h e a d l i g h t s when approaching ano the r v e h i c l e a t n i g h t .

H I G H INTENSITY PRESENCE LIGHTS. While i t w i l l be u s e f u l

t o o b t a i n h igher s i g n a l i n t e n s i t i e s under degraded v i s i b i l i t y

c o n d i t i o n s by means of t h e manual o v e r r i d e swi tch it would a l s o

be v a l u a b l e t o improve t h e marking of t h e v e h i c l e under t h e same

c o n d i t i o n s . For t h i s reason it i s recommended t h a t t h e i n t e n s i t y

of t h e p r e s e n c e l l i g h t s be r a i s e d t o v a l u e s t h a t f a l l between t h e

minimum and maximum i n t e n s i t i e s f o r n igh t t ime s i g n a l s . This can

r e a d i l y be achieved i n systems which u s e f u n c t i o n a l s e p a r a t i o n of

presence lamps from s t o p lamps. Such a change can probably be

incorpora ted a t low c o s t . The presence lamp w i l l use a d u a l

f i l a m e n t bu lb t o provide both low and h igh i n t e n s i t y ( f o g )

presence l i g h t s . I f presence and t u r n s i g n a l s a r e i n one lamp,

t h e t u r n f i l a m e n t could be used. Therefore , t h e manual i n t e n s i t y

o v e r r i d e swi tch i n t h e high i n t e n s i t y p o s i t i o n would provide h igh

i n t e n s i t y s i g n a l s , i r r e s p e c t i v e of t h e s e t t i n g of t h e h e a d l i g h t

swi tch , and a l s o h igh i n t e n s i t y presence l i g h t s .

LAMP SEPARATION DISTANCE. I n ano the r r e p o r t it was

recommended (Finch, 1968) t h a t lamps having d i f f e r e n t f u n c t i o n s

he same should probably apply t o s i d e marker l i g h t s .

should be s e p a r a t e d by a minimum edge-to-edge d i s t a n c e of 3 .5

i n c h e s i n o r d e r t o provide c l e a r i d e n t i f i c a t i o n of t h e v a r i o u s

numbers of l i g h t s be ing shown. I n t h e s e s t u d i e s t h e u s e of number

coding has been found t o be a u s e f u l coding concep t , However,

b e f o r e number coding can be e f f e c t i v e it must be r e a d i l y per-

ce ived and f o r t h i s reason lamps should be s e p a r a t e d by some

minimum d i s t a n c e . Other s t u d i e s (AMA, 1966; Mortimer, 1969a)

have found t h a t t h e s e p a r a t i o n d i s t a n c e r e q u i r e d between two

lamps i n o r d e r t h a t t h e y be perce ived a s s e p a r a t e l i g h t sources

i s a f u n c t i o n of t h e viewing d i s t a n c e , b u t n o t of t h e lamp a r e a .

I t was found (Mortimer , 1969a) t h a t a n edge-to-edge s e p a r a t i o n

d i s t a n c e of 6 inches was needed between a presence lamp of 8 c p

and a s i g n a l lamp of 1 2 0 cp f o r them t o be seen a s s e p a r a t e l i g h t

sou rces on 90 pe rcen t of occas ions a t a viewing d i s t a n c e of 400

f e e t . A t 300 f e e t t h e analogous s e p a r a t i o n d i s t a n c e was 5 inches ,

I f a c r i t e r i o n of 300 f e e t i s s e l e c t e d t h e n t h e edge-to-edge

d i s t a n c e between lamps should n o t be l e s s t h a n 5.0 inches t o ensu re

t h a t t h e number of lamps shown on t h e v e h i c l e w i l l be v i s i b l e

w i t h a p r o b a b i l i t y of 9 0 p e r c e n t . This c r i t e r i o n should be

a p p l i e d t o lamps which a r e f u n c t i o n a l l y s e p a r a t e d and which a r e

cont inuous burn ing i n o p e r a t i o n , s i n c e those t h a t a r e i n t e r m i t t e n t

o r f l a s h i n g would be more r e a d i l y i d e n t i f i e d a s s e p a r a t e sou rces .

For t h i s r eason it would be recommended t h a t s t o p s i g n a l s should

be s e p a r a t e d by an edge-to-edge d i s t a n c e of n o t less t h a n 5.0

f inches from p resence l i g h t s and t h a t t u r n s i g n a l s should be

s e p a r a t e d by an edge-to-edge d i s t a n c e of n o t less t h a n 3.5 inches

from p resence and s t o p lamps.

LAMP LOCATION. I n o r d e r t o p rov ide t h e maximum v i s u a l

a n g l e t o fo l lowing d r i v e r s a t n i g h t of a v e h i c l e ' s p resence

l i g h t s it w i l l be impor tan t t h a t t h e y a r e p l aced a s f a r o u t a s

p o s s i b l e on t h e v e h i c l e s t r u c t u r e . One p a i r of low mounted

p resence lamps should be mounted a t a h e i g h t of 15-25 inches ;

ano the r p a i r should be mounted a t t h e i n t e r s e c t i o n of t h e C - p i l l a r

with t h e r o o f l i n e . Rear t u r n s i g n a l s should be p laced a s c l o s e

a s p o s s i b l e t o t h e s i d e s o'f t h e v e h i c l e t o b e s t d e l i n e a t e t h e

d i r e c t i o n of t u r n be ing i n d i c a t e d and t o g i v e maximum v i s i b i l i t y

of t h e lamp. I t i s , t h e r e f o r e , recommended t h a t t u r n s i g n a l

lamps should be mounted i n t h e same v e r t i c a l p lane o r inboard ,

a t t h e same h e i g h t o r above, a s t h e low mounted presence lamps

s e p a r a t e d by a minimum edge-to-edge d i s t a n c e of 3.5 inches

from presence o r s t o p lamps, S top lamps should be a minimum

d i s t a n c e of 5.0 inches edge-to-edge from presence lamps, n o t

outboard of t u r n lamps, and a t a h e i g h t of 15-30 inches . T h i s

requi rement w i l l probably d i c t a t e t h a t s t o p lamps be mounted

inboard on t h e v e h i c l e s t r u c t u r e i n a system which uses s e p a r a t e

p resence , t u r n and s t o p lamps.

COASTING SIGNAL. A s tudy was a l s o conducted i n t h i s pro-

gram aimed a t developing an a n a l y s i s of t h e u t i l i t y of s i g n a l s

which i n d i c a t e t h a t a v e h i c l e i s i n a c o a s t i n g mode, wi th t h e

a c c e l e r a t o r r e l e a s e d and t h e b rakes n o t a p p l i e d , This work was

c a r r i e d o u t by ins t rument ing a v e h i c l e which was subsequent ly

used by U n i v e r s i t y personnel i n v a r i o u s t r i p s on expressways,

c i t y s t r e e t s , and r u r a l roads . Measurements were taken of t h e

a c c e l e r a t o r and brake pedal a c t i v i t y a s measured by a c c e l e r a t o r

r e l e a s e and brake a p p l i c a t i o n s . The t o t a l time of each a c c e l e r a -

t o r r e l e a s e , dur ing which t h e v e h i c l e coas ted p r i o r t o t h e a p p l i -

c a t i o n of t h e a c c e l e r a t o r o r t h e b rakes , was measured a s w e l l a s

t h e v e l o c i t y of t h e v e h i c l e a t t h e beginning and end of each of

t h e s e sequences. The r e s u l t s showed t h a t a c c e l e r a t o r r e l e a s e

was fol lowed by a p p l i c a t i o n of t h e b rakes i n n o t more than 38

p e r c e n t of c a s e s w i t h i n a p a r t i c u l a r speed range , of t h e f o u r

speed ranges which were s e l e c t e d between 0 and 80 mph. When a

c l o s e r a n a l y s i s was made of t h e t ime i n t e r v a l between a c c e l e r a -

t o r r e l e a s e and b rake a p p l i c a t i o n it was found t h a t t h e e lapsed

t i m e was r a r e l y 0.5 seconds o r l e s s . This time i n t e r v a l was s e l e c -

t e d a s r e p r e s e n t i n g t h e t r a n s p o r t t ime of t h e f o o t from t h e a c c e l -

e r a t o r t o t h e b rake , and was s h o r t enough t o sugges t t h a t t h e d r i v e r

wished t o o b t a i n braking f a i r l y soon fol lowing a c c e l e r a t o r r e l e a s e .

I t should be noted t h a t , i n an emergency s i t u a t i o n r e q u i r i n g

r a p i d b rak ing , f o o t t r a n s p o r t t ime i s more l i k e l y t o be on

t h e o rde r of 0 . 2 5 seconds. On t h i s b a s i s it was concluded t h a t ,

i n t h e major i ty of i n s t a n c e s when t h e a c c e l e r a t o r was r e l e a s e d ,

t h e r e was no need t o r a p i d l y apply t h e b rakes . Therefore ,

a c c e l e r a t o r r e l e a s e could not be taken a s a r e l i a b l e i n d i c a t i o n

t h a t t h e brakes were subsequently app l i ed t o o b t a i n a r e l a t i v e l y

l a r g e v e h i c l e d e c e l e r a t i o n . For t h e s e reasons , i f a s i g n a l was

given whenever t h e a c c e l e r a t o r was r e l e a s e d it could no t be

i n t e r p r e t e d a s being one t o i n d i c a t e t h a t brake a p p l i c a t i o n

would fo l low o r t h a t , i f braking d i d occur , t h e r e s u l t i n g

d e c e l e r a t i o n l e v e l would be moderately high. This i s not

s u r p r i s i n g s i n c e another s tudy (Mortimer and Segel , 1970) found

t h a t i n only 4 . 5 pe rcen t of brake a p p l i c a t i o n s d i d t h e peak

d e c e l e r a t i o n l e v e l exceed 0.3g. Therefore , t h e u t i l i t y of a

s i g n a l which would appear whenever t h e a c c e l e r a t o r was r e l e a s e d

a s an e a r l y warning of moderate t o severe braking was poor. The

a n a l y s i s was then conducted t o e v a l u a t e t h e p o s s i b l e r o l e of a

coas t ing s i g n a l t o warn fol lowing d r i v e r s t h a t t h e v e h i c l e ahead

of them was coas t ing f o r a f a i r l y long time p e r i o d , dur ing which

v e l o c i t y could be reduced s u b s t a n t i a l l y wi th an inc reas ing

p o t e n t i a l f o r a rear-end c o l l i s i o n . Because t h e a n a l y s i s had

shown t h a t on many occas ions when t h e a c c e l e r a t o r was re leased

t h e change i n v e l o c i t y of t h e v e h i c l e dur ing t h e coas t ing per iod

was l e s s than 2 mph it was n o t considered d e s i r a b l e t h a t a

coas t ing s i g n a l should be given whenever a c c e l e r a t o r r e l e a s e

occurred . I t had been suggested i n an e a r l i e r r e p o r t (Mortimer,

1967) t h a t such a s i g n a l provided l i t t l e informat ion of importance

t o a fol lowing d r i v e r , due t o t h e smal l change i n v e l o c i t y ,

and would occur wi th high frequency caus ing p o t e n t i a l d i s t r a c t i o n

t o more important s t i m u l i . I t was hypothesized, however, t h a t i f

c o a s t i n g continued f o r a f a i r l y long time per iod v e h i c l e v e l o c i t y

would d e c r e a s e s u b s t a n t i a l l y and t h a t a s i g n a l should then be

g iven t o a fo l lowing d r i v e r . The d a t a i n d i c a t e t h a t such a

s i g n a l should be g iven 5 seconds a f t e r t h e a c c e l e r a t o r i s

r e l e a s e d . Such a s i g n a l w i l l n o t occur f r e q u e n t l y , b u t may have

i n f o r m a t i o n a l p r o p e r t i e s when i t does occur . I t cou ld , t h e r e f o r e ,

be cons ide red a s a r e l e v a n t s i g n a l b u t probably does n o t need

d i f f e r e n t i a t i o n from t h e b rake s i g n a l . I t would be recommended

t h a t fo l lowing a c o a s t i n g pe r iod of about 5 seconds t h e s t o p

l i g h t s on t h e v e h i c l e should be a c t u a t e d . This would provide a

warning t o fo l lowing d r i v e r s i n t h o s e i n s t a n c e s i n which c o a s t i n g

of t h e l e a d v e h i c l e had n o t a l r e a d y been d e t e c t e d by them.

The s i g n a l would be u s e f u l i n i n s t a n c e s i n which long

c o a s t i n g pe r iods t end t o b e encountered such a s i n approaching an

e x i t ramp on a high-speed r o a d , a s t o p s i g n , t r a f f i c s i g n a l , o r

p r i o r t o t u r n i n g .

CONCLUSIONS

I t i s b e l i e v e d t h a t t h e r e s u l t s of t h e s t u d i e s t h a t have

been r e p o r t e d , t aken t o g e t h e r w i t h d a t a p r e v i o u s l y a v a i l a b l e

from o t h e r r e s e a r c h e r s , p rov ide a bulk of in fo rmat ion which may

be u s e f u l f o r t h e recommendation of an i n t e r i m improved r e a r

l i g h t i n g s t a n d a r d . The i m p l i c a t i o n of improved coding t echn iques

has been demonstrated t o p rov ide improvements i n d r i v e r performance.

D i f f e r e n c e s between exper imenta l systems,whose conceptual

b a s e s can be recomrnended,and t h e p r e s e n t system concept r e s u l t e d

i n g r e a t e r changes i n d r i v e r performance than t h o s e t h a t could

be d e t e c t e d a s a r e s u l t of d r i v e r s consuming moderate amounts

of a l c o h o l . I t has been shown by means of an a n a l y t i c a l c a r -

fo l lowing model, i n which conven t iona l and exper imenta l systems

were eva lua ted i n terms of t h e p robab le r e d u c t i o n i n rear-end

c o l l i s i o n s , t h a t s i g n i f i c a n t r e d u c t i o n s i n c o l l i s i o n s should be

found. An assumption which was used i n t h e model was t h a t c a r -

fo l lowing headways and v e l o c i t i e s would remain t h e same if v e h i c l e s

were equipped wi th experimental systems compared wi th systems

t h a t a r e now i n use . I t i s p o s s i b l e t h a t a r e d u c t i o n i n c a r -

fo l lowing headways may r e s u l t i f d r i v e r s pe rce ive t h a t t h e new

systems provide them wi th a d d i t i o n a l informat ion . I t i s con-

c e i v a b l e , t h e r e f o r e , t h a t t r a f f i c flow improvements may r e s u l t ,

t h a t r e d u c t i o n s i n rear-end c o l l i s i o n s may r e s u l t , and most

probably t h a t some combination of t h e s e two even t s w i l l occur .

The b e n e f i t s t h a t may accrue i n a c c i d e n t r e d u c t i o n from t h e use

of more s u i t a b l e s i g n a l i n t e n s i t y l e v e l s i n daytime cond i t ions

w e r e not eva lua ted b u t should n o t be d i s regarded . The use of

d u a l - i n t e n s i t y systems would have t h e added advantage of pro-

v i d i n g h i g h - i n t e n s i t y presence l i g h t s and s i g n a l s f o r use i n

degraded atmospheric c o n d i t i o n s t h a t occur i n many s e c t i o n s of

t h e U.S. I t i s a n t i c i p a t e d t h a t d r i v e r s would l e a r n t o use a

manual o v e r r i d e i n t e n s i t y swi tch a p p r o p r i a t e l y and t h a t it would

l e a d t o r e d u c t i o n s i n rear-end c o l l i s i o n s . The use of f o u r

presence lamps on a v e h i c l e i n which one p a i r i s mounted a t t h e

roof l i n e o r t h e C - p i l l a r and t h e o t h e r p a i r i n t h e i r p r e s e n t

l o c a t i o n s near t h e r e a r bumper w i l l p rovide improved d r i v e r per-

formance i n p rece iv ing headway changes t o h e l p them avoid

rear-end c o l l i s i o n s . Misperception of changes i n headway and

c l o s u r e r a t e a r e undoubtedly r e s p o n s i b l e f o r some rear-end

c o l l i s i o n s wi th t r u c k s on upgrades of t u r n p i k e s ( V e c e l l i o , 1 9 6 7 ) .

I t i s a l s o probably t r u e t h a t many rear-end c o l l i s i o n s w i t h

passenger v e h i c l e s could be a v e r t e d by t h e use of techniques t o

improve t h e d r i v e r ' s s e n s i t i v i t y t o changes i n headway. A system

of presence l i g h t s such a s t h a t desc r ibed was shown t o meet

t h i s o b j e c t i v e and f o r t h i s r eason i s recommended. There are

a l s o b e n e f i t s of added r e l i a b i l i t y and v i s i b i l i t y t h a t have

a l r e a d y been i n d i c a t e d t h a t would accrue from t h e use of v e r t i c a l

a s w e l l a s h o r i z o n t a l presence l i g h t mounting. S ide c o l l i s i o n s

such a s may occur when two v e h i c l e s s imul taneously merge toward

a c e n t e r l a n e on expressways a s w e l l a s i n o t h e r l a n e changing

o r t u r n i n g s i t u a t i o n s could be reduced by t h e use of a forward-

mounted r e p e a t e r t u r n s i g n a l a s desc r ibed . A coas t ing s i g n a l

which would appear whenever t h e a c c e l e r a t o r was r e l e a s e d was

found t o be undes i rab le . However, it was recommended t h a t t h e

s t o p s i g n a l s should be g iven when c o a s t i n g time exceeded 5

seconds i n o r d e r t o account f o r t h e reduc t ion i n v e h i c l e v e l o c i t y

which w i l l u s u a l l y be found t o occur wi th c o a s t i n g pe r iods of

t h i s d u r a t i o n o r g r e a t e r . Data taken from o t h e r s t u d i e s have

i n d i c a t e d t h a t a minimum s e p a r a t i o n d i s t a n c e , measured edge-

to-edge, of 5 .0 inches should e x i s t between s t o p lamps and

presence lamps and no t less than 3.5 inches between t u r n s i g n a l

lamps and presence o r s t o p lamps. The dimensional and i n t e n s i t y

s p e c i f i c a t i o n s by which t h e s e recommendations can be met have

been provided by t h e s t u d i e s t h a t were c a r r i e d o u t .

RECOMMENDATIONS

Based upon t h e r e s u l t s of t h e work t h a t has been r e p o r t e d ,

and on t h e f i n d i n g s of o t h e r s t u d i e s , a number of recommenda-

t i o n s which should l e a d t o improvements i n v e h i c l e r e a r l i g h t i n g

and s i g n a l i n g can be made. These recommendations a r e made wi th

r e s p e c t t o passenger c a r s b u t , wi th s u i t a b l e modi f i ca t ion , may

be a p p l i c a b l e t o o t h e r c l a s s e s of v e h i c l e s . The r a t i o n a l e by

which t h e s e recommendations have been de r ived have a l r e a d y been

d i scussed and w i l l n o t be r e i t e r a t e d .

1 , Rear s t o p s i g n a l lamps should be:

a. red

b. n o t combined wi th any o t h e r s i g n a l

c. s e p a r a t e d a minimum edge-to-edge d i s t a n c e of 5.0 inches from presence lamps

2 . * Rear t u r n s i g n a l lamps should be:

a . amber


c . s e p a r a t e d a minimum edge-to-edge d i s t a n c e of 3.5 inches from presence and s t o p lamps

o r , less p r e f e r r e d :

a . green-blue

b. combined wi th t h e presence lamp

c. s e p a r a t e d a minimum edge-to-edge d i s t a n c e of 5.0 inches from s t o p lamps

o r , l e a s t p r e f e r r e d :

a . r e d

b. combined w i t h t he presence lamp


-

*Only mutual ly e x c l u s i v e i tems i n 2 and 3 can be used.

3 . * Presence lamps? should be :

a . green-blue


c. s e p a r a t e d a minimum edge-to-edge d i s t a n c e of 3.5 inches from t u r n lamps, and 5.0 inches from s t o p lamps.

o r , less p r e f e r r e d :

a . green-blue

b. combined wi th t h e t u r n s i g n a l


o r , s t i l l l e s s p r e f e r r e d :

a . r e d


c . s e p a r a t e d a minimum edge-to-edge d i s t a n c e of 3.5 inches from t u r n lamps, and 5.0 inches from s t o p lamps

o r , l e a s t p r e f e r r e d :

a . r e d

b. combined wi th t h e t u r n s i g n a l


4. Low mounted presence lamps should be:

a , n o t less than 15 inches o r more than 25 inches v e r t i c a l l y

b. one a s c l o s e t o each s i d e of t h e v e h i c l e a s p o s s i b l e

Two a d d i t i o n a l high-mounted presence lamps should be:

c , l o c a t e d one a t each r e a r roof ( t o p ) co rner f o r v e h i c l e s wi th f i x e d C - p i l l a r s , o r

d o a s high and outboard a s p o s s i b l e , e .g. ,on t h e wa i s t - l i n e , f o r c o n v e r t i b l e s .

*Only mutual ly e x c l u s i v e items i n 2 and 3 can be used.

h he r e a r s i d e marker l i g h t must be t h e same c o l o r a s t h e presence l i g h t .

Rear t u r n s i g n a l lamps, when n o t combined w i t h presence

lamps, shou ld be mounted:

a , s o t h a t no p a r t of t h e lamps i s below o r ou tboard of t h e low-mounted p re sence lamps

b . a s f a r ou tboard a s p o s s i b l e

c . one lamp on each s i d e

Rear s t o p s i g n a l lamps shou ld be:

a , a t n o t less t h a n 15 i n c h e s n o r more t h a n 30 i n c h e s v e r t i c a l l y

b. i nboa rd of t h e t u r n lamps

c , a s f a r ou tboard a s p o s s i b l e

d. one lamp on each s i d e

Amber, r e p e a t e r , t u r n s i g n a l s , one on each s i d e shou ld be:

a . mounted w i t h t h e H-V a x i s of t h e lamps a t n o t less t h a n 33 i n c h e s no r more than 48 i n c h e s , v e r t i c a l l y

b. as f a r forward a s p o s s i b l e and n o t f u r t h e r t o t h e r e a r of t h e v e h i c l e t han t h e f r o n t wheel s p i n d l e

c . f l a s h i n phase w i t h f r o n t and r e a r t u r n s i g n a l s on t h e same s i d e

d. a t i n t e n s i t i e s d e s c r i b e d i n Table 4 , 7

Rear , t u r n and s t o p s i g n a l lamp i n t e n s i t i e s shou ld be a s

d e s c r i b e d i n F i g u r e s 2 . 6 , 2 . 7 and 2 . 8 f o r r e d , amber and

green-b lue s i g n a l s .

Rear , t u r n and s t o p , and s i d e , t u r n s i g n a l i n t e n s i t y

should be c o n t i n g e n t upon t h e p o s i t i o n of t h e headlamp

swi t ch :

a . day i n t e n s i t y s i g n a l s a r e t o be o p e r a t i v e when t h e

h e a d l i g h t s a r e n o t i n u se .

b. n i g h t i n t e n s i t y s i g n a l s a r e t o be o p e r a t i v e when

t h e h e a d l i g h t s a r e i n u se

An i n t e n s i t y o v e r r i d e s w t i c h i s t o be provided f o r u se

i n f o g o r o t h e r degraded v i s i b i l i t y c o n d i t i o n s :

a , of a t y p e recommended ( e . g . , r o c k e r , t o g g l e , r o t a r y )

b. c l e a r l y l a b e l e d t o i n d i c a t e i t s purpose and s t a t u s ,

c . when i n t h e "high" i n t e n s i t y p o s i t i o n , w i t h head- l i g h t s i n u s e , s i g n a l s a r e o p e r a t i v e a t t h e day i n t e n s i t y

d . when i n t h e "normal" i n t e n s i t y p o s i t i o n s i g n a l s a r e o p e r a t i v e a t i n t e n s i t i e s determined by t h e headlamp swi tch p o s i t i o n

e . when i n t h e "high" p o s i t i o n a n o t i c e a b l e feedback a u d i t o r y o r v i s u a l s i g n a l i s g iven w i t h t h e s t o p s i g n a l , b u t f o r n o t longer t h a n about 2 seconds

When t h e i n t e n s i t y o v e r r i d e swi tch i s i n t h e "high"

p o s i t i o n , w i t h h e a d l i g h t s i n u s e , presence l i g h t i n t e n -

s i t y should be r a i s e d t o t h e n i g h t s i g n a l i n t e n s i t y

range f o r t h a t c o l o r , shown i n F i g u r e s 2 . 6 o r 2 . 8 .

When t h e a c c e l e r a t o r i s f u l l y r e l e a s e d t o t h e i d l e pos i -

t i o n f o r 5 seconds o r longer t h e s t o p s i g n a l should be

o p e r a t i v e .

Appendices

Appendix A-1

MULTI INTENSITY STUDY INSTRUCTIONS

DAYTIME, I n t h i s experiment we want t o g e t your r e a c t i o n s

t o t h e i n t e n s i t y of v a r i o u s l i g h t i n g systems. On t h e board i n

f r o n t of you one o r more l i g h t s w i l l appear and grow g r a d u a l l y

i n i n t e n s i t y . Imagine t h a t t h e s e l i g h t s a r e t h e b rake s i g n a l s

of a v e h l c l e i n f r o n t of you, When a l i g h t system has become

b r i g h t enough s o t h a t i f it were t h e brake s i g n a l of a n o t h e r

v e n i c l e , you would cons ide r it adequate , respond by p r e s s i n g t h e

pushbutton you have been g iven. An adequate ly b r i g h t b r a k e l i g h t

would be one you f e e l would c e r t a i n l y a t t r a c t your a t t e n t i o n t o

it. A f t e r t h e l i g h t has reached a c e r t a i n b r i g h t n e s s , which

i n c i d e n t a l l y has no th ing t o do wi th when your b u t t o n s a r e pushed,

it w i l l f l a s h o f f b r i e f l y , and when it comes back on it w i l l

begin t o d iminish i n i n t e n s i t y . P r e s s your b u t t o n aga in f i r m l y

once and r e l e a s e it immediately when t h e l i g h t has reached a l e v e l

such t h a t it would no longer be adequa te ly b r i g h t were i t a

v e h i c l e ' s brake s i g n a l . I f t h e l i g h t should never r each a l e v e l

which you would deem adequate , do n o t respond.

A f t e r one l i g h t i n g system has completely d iminished, ano the r

system w i l l appear . The speed a t which l i g h t s grow b r i g h t e r w i l l

vary. P l e a s e ho ld your pushbuttons away from t h e o t h e r s u b j e c t s

s o t h a t they a r e n ' t a f f e c t e d by your responses . Also p l e a s e do

n o t smoke dur ing t h e experiment . Do n o t d i s c u s s any a s p e c t s of

the experiment u n t i l i t i s completed, You may ask m e any ques-

t i o n s you have regard ing t h e t a s k you a r e t o perform. NOW,

b e f o r e some p r a c t i c e r u n s , do you have any q u e s t i o n s ?

O K , i f you w i l l watch t h e l i g h t board , we w i l l begin w i t h a

few p r a c t i c e t r i a l s .

NIGHTTIME. I n t h i s experiment we want t o g e t your r e a c t i o n s

t o t h e i n t e n s i t y of va r ious l i g h t i n g systems, On t h e board i n

f r o n t of you one o r more l i g h t s w i l l appear and grow gradua l ly

i n i n t e n s i t y , Imagine t h a t these l i g h t s a r e t h e brake s i g n a l s

of a v e h i c l e i n f r o n t of you. When a l i g h t system has become s o

b r i g h t t h a t i t would be uncomfortable t o view, were it t h e brake

s i g n a l of another v e h i c l e , respond by p r e s s i n g t h e pushbutton

you have been given, Push your but ton f i rmly once and then

immediately r e l e a s e it. A f t e r t h e l i g h t has reached a c e r t a i n

b r i g h t n e s s , which i n c i d e n t a l l y has noth ing t o do w i t h when your

bu t tons a r e pushed, it w i l l f l a s h o f f b r i e f l y and when it comes

back on i t w i l l begin g radua l ly t o diminish i n i n t e n s i t y . P ress

your bu t ton again f i r m l y once and r e l e a s e i t immediately when

the l i g h t has reached a l e v e l such t h a t it i s no longer uncom-

f o r t a b l y b r i g h t , keeping i n mind t h a t you a r e t o imagine t h e

l i g h t a s a brake s i g n a l on another v e h i c l e . Thus, we a r e n o t

asking you t o respond when it i s j u s t t o o b r i g h t t o be r e a l l y

comfortable f o r viewing purposes, s i n c e a brake l i g h t should be

b r i g h t enough t o be a t t e n t i o n g e t t i n g . Rather we want you t o

respond a t a p o i n t where t h e l i g h t i s d e f i n i t e l y t o o b r i g h t .

I f t h e l i g h t should n o t reach such a l e v e l , do n o t respond. I f , on t h e o t h e r hand, t h e l i g h t g e t s s o b r i g h t t h a t a t a p o i n t

beyond where you have pushed your but ton it becomes p a i n f u l l y

b r i g h t , t r y t o keep looking a t i t , b u t s q u i n t and t u r n your eyes

s o t h a t you a r e n o t gazing d i r e c t l y a t t h e l i g h t . Then when t h e

l i g h t begins t o dim t o where it i s s t i l l uncomfortable b u t no

longer p a i n f u l t o view, look d i r e c t l y a t it again s o you can be

ready t o respond j u s t a t t h e p o i n t where it i s no longer uncom-

f o r t a b l e .

A f t e r one l i g h t i n g system has completely diminished another

system w i l l appear. The speed a t which l i g h t s grow b r i g h t e r w i l l

vary. P lease hold your pushbuttons away from t h e o t h e r s u b j e c t s

s o they a r e n o t a f f e c t e d by your responses . Also p l e a s e do n o t

smoke dur ing t h e experiment . Do n o t d i s c u s s any a s p e c t s of t h e

experiment u n t i l i t i s completed, You may ask me any q u e s t i o n s

you have regard ing t h e t a s k you a r e t o perform. NOW, b e f o r e

some p r a c t i c e r u n s , do you have any q u e s t i o n s ?

OK, i f you w i l l watch t h e l i g h t board we w i l l begin wi th a

few p r a c t i c e t r i a l s ,

Appendix A-2

Tables A-2.1-2.32

Cumulative Percent Day (Adequate), Night (Intolerable) Intensities, at 75 and 270 Feet, for Normal and Color-Blind Subjects, as a Function

of Lamp Area and Color

TABLE A-2.1. CUMULATIVE PERCENT DAY ADEQUATE CANDLEPOWER FOR WHITE A S A F U N C T I O N OF L A M P - A R E A ,

. . . - . . . . . . . NORMAL -- ...... SUBJECTS .- .... -- ......... AT -- 75 ..... FEET - ......... . . . . . . .

AREA I S Q e I N C H E S ) PC T 4 e.0 6 . 1 1 2 . 6 2 5 . 2 3 7 0 8 1 2 a 6 H

TABLE A-2.2. . . . . . . . . . CUMULATIVE PERCENT D A Y ADEQUATE ... - - . - - - CANOLEPOWER -. .. . .. . . . . . . . . .- - - - - -. RED..- *S ..A-F-"NCT.I.ON.. OF L A M P A R E A , . .

. . . . . ---- NORMAL --..--- SUBJECTS -- AT 75 ---.. FEET

. . . . . AREA (SQ. . - INCHES) . . PCT 4.0 6.1 12.6 2 5 . 2 -- -37. 8 12.6H

LOO 1427. 2962. 6280, 11.571. 8 2 5 3 . 5244 .

TABLE A-2.3. C U M U L A T I V E PERCENT D A Y AOEQlJATE CANOLEPOWER FOR A M B E R A S A - F U N C T I O N OF L A M P A R E A ,

NORMAL SUBJECTS AT 75 FEET._ . - - . . . - . . - - - - - . - - . .. . -. .- - - - . - .- - .. ,

AREA (SQ. INCHES) PC T 4 . 0 6 . 1 12 .6 2 5 . 2 3 7 . 8 12 .6H

. . TABLE A-2.4. . . . . CUMULATIVE PERCENT DAY AEQU_ATE.C!NDCEPOWER FOR GREEN A S A-FUN-CTION OF L A M P A R E A ,

NORMAL SUBJECTS AT 75 FEET _ _ _-_ ___ _. _______________l__l__ -. - . -

AREA (SQ. INCHES) . . . . . . . . . . . . - - . . -. .-

PC T 4 .:O 6 . 1 12.6 25 .2 3 7 . 8 1 2 0 6 H

.. . . T ~ H L ~ . A-2.5. WM!JLAT I V E P E R C E N T ? A Y PDE-QUASE-LANDCEPC~ER . . . .. .~ -.

F C R h k I T t A S A FUhCTIOh CF L A M P A R E A , h C f 4 P A L S U B J E C T S A T 270-1 EL_---.-.--.-.

A R E A . (SQ. INCHES) PC T 4 • C 6.1 12.6 25.2 37.8 12.6k

... Tn.KI.E. ?-2.6,. .cU_!_U.CLAT I V_E P E R G N CAY.. ?D._EQUPI_E_-._C_nNCCEP_Ck_ER . . - . . - . . . . . . . . .

FOR R E D A S A FUNCTION OF L A M P A R E A * NERPAL SUBJECTS A T 270 F E E T - . -- ---- -- .-------- ---------------------.--..

.....- . . . . . . .... -AREA._ !.sQ.?. I-NCHES) -. P C T 4.0 6 .1 12 .6 25.2 37. 8 12.6H

. TA_ULE A-~*~*-.-C_UM_LJL_AT!VE P.t.RC-E&I. JAY-DECUA.LC__C._ANCLEPCbER.. .~ - -

FOR A M B E R A S A FUNCTION OF LAMP A R E A * N O H I ~ A L S H J E C T S A T 2 7 0 F E E L -- -

T A B L E .._A:.2.._H CUFULJTIVE PERCENT. Day._ LrDSQ_UAI~-.CAN~l,EP_CklEK . -. . . -. . . - -- .. . - .. . - .

F C R GWEEh A S A F U h C T I O N C F LAMP A R E A , ,.- . . - - - NO&b'AL SUBJECTS A T 270 F E E T -- -- --- -- -

. . . . 4 ~ ~ a ( S-Q, I N C ~ . .. . . .

P C T 4 • C 6 0 1 12.6 25 .2 37.8 1 2 o 6 h

TABLE . . A-2.9. . . CUMULATIVE . .. . . . . P E R C E N T DAY AOEQUAT-E---CANDLEPOKE-R FOR--WHITE- - A S A-FUNCTION O F L A M P A R E A ,

COLOR-BLIND SUBJECTS AL..l5.-L!?EI . .... .. - ..-- . - . . -. . ---. . -- - -- .- ..

A R E A ( S O . . INCHES) .

P C T 4.0 6 .1 i2.6- 25.2 37 8 12.6H

LOO 9663. 22650. 31091. 68925. 47160. 30625.

I?ABLE-A-2.10.: CUMULATIVE PERCENT DAY ADEQUATE CANDLEPOWER . . . . . . - - - . . - . . - . - . . . - .

FOR R E D AS A FUNCTION OF LAMP A R E A * COLOR-BLIND SUBJECTS AT 7 5 FEET - .- - - .- -- - - -- - - -- . . . . - . . . .. . . .. . . -.- - - -- - -

AREA .- ( $ 4 . ..-. I N C H E S ) .- -. - . . . ... .. . . . . - . . . .

QCT 4 LO 6 a 1 12.6 25.2 37.8 1 2 . 6 ~

TABLE A-2 .11 . CUMULATIVE PERCENT D A Y ADEQUATE CANDLEPOWER F O ~ AMBER A S A FUNCTION OF LAMP A R E A ,

COLOR-BLIND SUBJECTS A T 7 5 FEET . -. -- -- - -- .- - . . ----- . -. -. -- -- . -

QCT .. .

5

10

1 5

20

25

30

3 5

40

45

50

5 5

60

65

7 0

75

80

8 5

90

95

LOO

AREA ( S Q * INCHES) 1 2 . 6 2 5 . 2 3 7 . 8

TABLE A-2.12.: . . . . . . . CUMULATIVE PERCENT D A Y ADEQUATE .oF..-LblnP... CANDLEPOWEH . . . . . .

.GHEEN * $ --*. -F"NCT COLOR-BLIND SUBJECTS AT 7 5 FEET ........ . - ......... -- . - . -- - .. - . - -- -- -- .... - ..-------.--- - -. --

. . . . . . . . - . AREA . . ( S O . - . INCHES) -

P C T - 4 .:O 6 . 1 12','6 25 .2 ' - - - - - 37.8 12.6H

..T4t;iLE A-2,13, C U P b L 4 T I V E P E R C E N T C A Y A D E C U A T E C A N D L E P O W E R FCR h H I T E A S A F U h C T I O k CF L 4 M P A R E A ,

.- - .- -- .- - -- C O LOR-BL --- I kRS!&JECTS-_AL_21P-FEf _. .

A R E A ( S c . I N C E E S ) . PCT 4 .0 6 . 1 12.6 2 5 . 2 37.8 12.6P

T_ABL.fr A - 2 - 14 . C I J M U L A T I V E P E k C E N T D A Y ADf 6IUATE JANDLlEYeWER - .

F C R R E C A S A F t J N C T I C N CF LAPP A R E A * C C L O R - B L I A D S L e J E C T S A T 270 F E E T - . . . -- -- -. . - - - - - - - - .-- - -. .- - . . --- .- - -. . . - .- - .- - . . - .- .- - . -- . -. - . .. . - -. - - - . - -. -

12.6l- -. - . - -. -

192.

455.

? 17 ?..

769,

e2c.

9 9 2 4 ..

1164.

1 2 3 5 ,

13( '6,

1 9 3 1 .

1 7 5 6 .

1817,

1 8 7 8 .

2111.

2 3 4 ' 3 .

2343.

2343.

31) 15

! t P h *

4 3 3 3 .

TABLE A-2.15. C I J M U L A T I V E PERCENT D A Y .A.DEQUATE_ CANDCEPOWER FCR AtJF!ER A S A F U N C T I O N O F L A M P A R E A *

C C LC K:BUho-.S&_JECT.S. .-!!L2_71) F E E 1 . . .. . ..-. - - .. . ... . -- . .. - -- -

AREA (SQ. INCHES) PC T 4.0 6 . 1 12.0 25 .2 37. F( 1 2 e 6 t i

1 C 3 4 4 . t @ Z . 1174.. 1C20. 1 4 6 3 . 8 5 5 .

TA-BLE A - 2 . 1 6 , C L P U L J T I V E P E R C E N T C A Y ADfQUA-TE C A N G L E P C K E R F C R G K E E h A S A F L N C T I O R CF L A M P A R E A ,

COLOR-BLINI ' ) S U B J E C T S _ A I - 2 7 Q - F . S E T . . -4.. . . . - . . - .-

. P R E P ( S G . IFUCPESI PC T 4.C 6 .1 12.6 25.2 37.R 12.6b

TABLE A-2.17. CUMULATIVE PERCENT NIGHT INTOLERABLE CANOLEPOWER FOR WHITE A S FUNCT ION--OF L A M P A R E A ,

- . -. . . - . . . . . . . - . NORMAL -. . - - --. . - SUBJECTS - -- - AT -- 75 . FEET -. - - - - .. . - . - . . . .

A K E A (SQ. I N C H E S ) PC T 4.0 6. 1 12.6 25.2 37.8 12.6H

80 2415. 3418. 49350 6125. 77180 6146.

8 5 3193. 4026. 8407. 701He 9127. 7591

90 484 1. . . 4311. . - 9703 - .. . . 7825. 11273. 8488,

95 6199. 8805. 103590 8973. 20694. 11108.

L O C 13850. 34000. 34460. 57960, 46083. 34231.

TABLE . - A-2.18.: . . . . CUMULATIVE ....... - - - . PERCENT - . .. -. NIGHT .- - - - . INTOLERABLE .- .. - --- .. -- . CANDLE POWER^---_- - - .. -- - - .... - - . - .

FOR RED A S A FUNCTION OF LAMP AREA, NORMAL SUBJECTS AT 7 5 FEET -. - -. . -- .. - - -. ... -. .... --- . - - -- - - --- . - - -- ----- -

AREA (SQ. INCHES) . . . . . . . . ......... . . . . . . . . - .

PCT 4 .:O 6.. 1 - 12 a16 2 5 . 2 3 7.. 8 12.6H

T A B L E A-2.19. C U M U L A T I V E . . P E R C E N T N I G H T I N T O L E R A B L E CANDLEPOWER FOR AMBER A S A FUNCTION OF L A M P A R E A ,

. . . . . . . . . . -- - -. . . . NORMAL . - - S U B J E C T S - - -. .- - . - A T .. --- 75 - --- F E E T . - - .

AREA (SQ. I N C H E S ) PC T 4.0 6. 1 12.6 25.2 37. 8 12.6H

. - -- . . . . - - -. .- . .

5 106. 153. 139. 154. 320. 1C8.

TABLE A-2.20.: - .. . . . CUMULAT .. ........... 1VE .....-. CANDLEPOWER ............... - . -

FOR GREEN A S A FUNCT-ZON OF LAMP AREA* NORMAL SUBJECTS A T 75 FEET ... .. -- --- .---- - ---.-- ..... . . ---.- -. --- - -- - - . -- .- - - .............. .

AREA ( S O . .. .- INCHES) PC T 4.0 6.1. - - 1.2 .'6 25.2 3 i'. a;- 1 2 . 6 ~

LOO 1408. . 2860. ~ . . 4730. . - 8788, 7250. 4680.

T A B L E A - 2 . 2 1 . C U M U L A T I V E P E R C E N T N I G H T I N T O L E K A H L E C A N D L E P C W E R FCR k t - ITE A S A F U N C T I C N C F L A P P A R E A ,

.. ..- . .. .. . .. . . - - .... - ... .. . r\cl!PAL. SCUJECZS A T ... 2 7 C . F.EET .. .

T A H L f . . . . . . A-2 .22 , C U M L L A T I V E - PEi?CENT h1GHT I F v T P L E K A B L E ~ C A h ' O L E P C k i E K FOR K E D A S A F U N C T I O N OF L A M P A R E A ,

A C K P A L S L E J E C T S . A T 2 7 0 F E E T - . . - -. . .. . .- . . - . - .. -

P K E A ( S Q . IhCHESl 12.6 2 5 . 2 3 7 . @

T A B L E A-2.23. C U ~ M I j L A T I V E P E R C E N T hlGHT 1tVTCLEKA.BLE CANDLEPOkEV, F C K A P B E K A S A F U N C T I O N OF L A P P A R E A ,

C M b L SU EJECTS- AT - 2.7 C. F k LT - . .. . - . - . - - .. - - -- - - . - - - - - . .- - -- . . . . - . . - - . .. - - - . - . . .- . - .

P K E A ( S G . I b C b E S ) P i.. T 4 . 0 6 . 1 1 2 , h 25 .2 37 .0 1 2 . 6 b

_ T A R L - E A--2.24. CUMULATIVE P E R C E N T N I G H T INTOL-EKABLE C A N O L E P C W E R . .

FCH G j t t t K A S A FUNCTION G F L A P P A R E A , hCRPAL SUBJECT'S AT 270 FEET .~ -- --. -- - . -- --- -- - . . - . . . . - .- .. . . - . -. .

. A f i E A fS .Q . . . INCHES) P C T 4 . 0 6.1 12.6 25.2 37.8 1 2 0 6 P

- . . . . . . . . .. - - - - . . - - - . . .- . . -. .- --. .- . -- - - -. -. -- . . .. - . .- ... - . .-.~ -. . .- - .

5 41. 1 4 1 . 5 7 0 5 3 . 1 6 9 - 4 4 •

1 . . - 6 E * . .A??.%... . 2-5 6 - .. ... 2?7! 2 ' 1 7 . 1 7 6 .

2 0 Y C . 2 2 2 . 3050 ? q 7 0 2 ' 3 7 . 222 .

TABLE . . . . . A-2.25,' . . . . CUMULATIVE -. ......... PERCENT A.i -A NIGHT .FU.Kt-TION INTOLERABLE AMP CANDLEPO-WE&_ .iR-Er ,-.- - .

COLOR-BLIND SUBJECTS AT ... 7 5 . FEET ....... . . . . . - .. - ........................ - - - -- ...... - - --- - . - - - --. - .. -- - - - - - - -. - ... - - - . - . - . . . . - .......

. ... A R E A ( S Q a INC~WES! _ . .

PCT 4.0 6 .1 12.6 2 5 2 37.8 1 2 . 6 ~

75 ? 8 1 9 * . . . . . . . . 6915. . . . . . . . . . . . . . . . . . . . . . . . 6001. 11330. 12893.

80 2859. 9287. 7923. 13794. 17083,

8 5 6163. 10426. 11542. 27997. 19123,

. . 9 0 -- . . . . . 10 5 56, . . . ... . .. . . . . . . . . . . ... 11154. - - -. - -. 15727, -. - - 46113. - 20446. - -

95 13850, 13930, 21764. 63255. 26044

LOO 13850. 22850. 33358. 77475. 44469.

COLOR-BLIND SUBJECTS AT 75 FEET ^ ._ ------------.- ------- I_-- -

AREA ( S O . INCHES) - ~. .- - - . - .. PC T 4 .:o 8 ; i".~ 12-;6 25.2 - 31.8 12 . - b ~

LOO 1680. 3475. 6 2 0 0 . 15275 _ 10150. 6 1 R O

TABLE A-2.27.. CUMULATIVE -.. PERCEP(T NIGHT I N T O L E R A 3 L E - CANDLEPOWER ~ ...

FOR AMBER AS'A '?UNCTION OF L A M P A R E A , COLOR-BLIND SUBJECTS AT 75 F E E T - - . . . - . - . - - -- . - -. . . . . . . - - . - - - -. .. - - ---.- - - - -- - - --. - . . - . - - - . - - . - - - - . . -. - -- ... - - . - .

A R E A . . . ( S Q o - . INCHES-) PCT 4.0 60 1 12.6 25.2 37.8 12.6H

LOO 4730. 12980. 18000. 34150. 30000. 200000

TABLE A-2.28., CUMULATIVE PERCENT NIGHT lNTOLERABLE CANDLEPOWEK . . . . . . . . . - . . - - . . . . . . . . FOR - .... GREEN - *$-. * $-" .N-c- T.I.~6 fi.--o.k. CAMP- AREA.r' .. .......

COLOR-BLIND SUBJECTS A T 75 FEET . - - - . - . - - - - -- - - .- -- - - .. -- -.------ -------- ..-

. . ~ . . ... .... AREA (SQ. ......... INCHES) . . . - .... - -. . . . . .

PCT 4 .:O 6 . 1 12.16 2 5.2- 3 7 . 8 1 2 . 6 ~

T A B L E A-2-29, C U M L L A T I V E P E R C E h T 4 I G H T I h ! T C L E R A @ L E C A N D L E P G k E R F C R W H I T E A S A F U d C T I C N OF L A M P A R E A ,

C C L C H - B L I N D S U E J E C T S A T 7 Q . F E k T . . - . . .. - -. . - - . . - . - - .- -- - - -- -- - - - - . -- - . .. -. . . - -. - . - -- . - . . - - . - - . - - - - - - . - - -

P C T 4.0 . ~ - . -. - . . . .

5 1 2 9 .

1 C 1 9 s .

15 .- ... 274 ,

Z C 3 5 4 .

2 5 45C.

3 Q. 5 4 t .

3 5 a 19 . 4 1; 1 l 5 i .

ft 5 1 4 6 5 .

ri C 173C.

5 5 1 :? ( 9 5 . 6L' 2 1 1 2 .

t~ 5 2 7 0 2

7 (; 3 4 C ; k .

7 5 1") 7 9 .

ei; 5551.

1' 5 6 7 4 1

,3 C) i C P C 3 .

Y 5 13i150.

1 0 0 1 3 e 5 c .

A R E A ( S G . I h C F E S ) 12 .6 25.2 3 7, H 1 2 4 6 H

. . .

1 3 5 . 203. 383 . 3 5 1 ,

3 2 5 . 3A4. 529 . 6 6 9 ,

551.- - . 5 9 4 0 667 . 1C4 1.

755 . 867 . P!9. 147P .

P53. 1 3 2 0 0 1C12. 2 1 1 0 e

951. 1 7 8 5 > 1 2 0 5 . 2 7 4 2 .

1 5 5 5 . 2nC 5. 1 ( J 4 q m 3C46.

,272'1. 2 1 4 5 . 2 n 7 7 . 3 2 4 2 ,

3 0 ~ 3 . 2 3 4 C o 3 6 4 1. 3437 .

3 H 2 t e 2 7 0 0 . 3 9 1 2 . 3 6 3 2 0

4 5 6 3 . 3C6L1. 4 1 8 2 . 3 E 2 7 e

6 1 9 7 . 3 2 3 5 . 5 8 2 3 . 4 6 1 4 .

8 1 3 0 . 3 3 2 5 - 7921 . t C 7 7 .

1GG06. 43133. 9733 . 7 4 4 6 .

1 1 7 1 1 . 8 3 1 5 . 16719. S I T ; C .

1 3 4 1 6 . 1 2 2 4 7 , 1 1 6 9 9 . 1 0 8 5 4 .

2 4 0 4 5 . 34G11e 223YSa 22371 .

374411. 6 1 7 1 9 . 3 6 3 3 8 , 3 7 1 5 9 .

478533. 8 3 7 7 5 . 4c leh?. 4 e z 5 c .

47e5C. 6 8 8 7 5 . 5 7 1 4 6 . 4 8 2 5 0 .

.. T P P L t . A - ~ L Z O : CUM_U_IALLVE_. !'ERCEI\IT NI__G_H_T. !NTO_LEHABLE. CANDLCPCWER . -_.. F C R R E D A S A FUNCTICN CF L A M P A K E A ,

- ---- - -. -- C C L O K - B L I N D S U P J E C T S A T 270 F E E T .- ..---- ....

.... . . ........ -- R E A (SQ. I V C H E S I P C T 4.b 6.1 12.6 2 5 0 2 37.8 12.6H

TABLE A-2.31. C U M U L A T I V E P E R C E N T N I G H T I N T O L - E R A B L E C A h ' D L E P C W f H F C K A Y e E R A S A F 0 4 C T I C N C F L A K P 4 R E A t

C C L C R - B L I N C S U P J E C T S A T 27.0-FEET .. -. ---- - -. - - .. .- ~.

A R E A ( S W . I N C t - E S I P C T 4.C 6.1 12.6 25.2 37.8 12.6b

3 0

3 5

it 0

4 5

5 ( j

s 5

i; 0

t. '.,

7 0

7 5

F O

8 5

90

9 5

L O O

T A B L E A-2..32. CUMUI-ATIVE PE-RC-ENT. l \ i IGHT [ N T O L E R A B L E _ C A N O L E P C W E : i { F C H GREEh A S A F U f V C T I C N OF LAMP A R E A ,

C C L O R - E L I N D S U e J t C T S A T 2 7 0 -FE.ET. . . - . - - . . . . . . . - - . . . .- - - - -. - -. . . -- - - - - -. .. -- . - - -. - -- - -. .- . - - - . - . . - - . - - - - .... - .. . -

4.C 6 .1 . . . - . . . . - . - .- .- . . . . .

5 5 . 39.

65. C 9 .

.. . 7(?? ~ 1.938

e z . 151.

112 , 2 4 3

! 4 ? . - -. . 335.

1157. 4 0 1 .

151. 450.

227. 5 0 u o

2 3 7 . 5 3 6

3 6 7 . 5 6 5 .

0 3 7 . t $ 2 . - -

1101 . 7 2 4 .

14CE. e C 8 .

1 4 0 8 . .- e sz .

14GP. 956.

1408 . 1540 .

14CP. 2 2 5 4 r

140e 2 8 6 0 .

1 4 c e , 2 e 6 c .

- .

A R E A ( S O . I N C P E S ) 12.6 25.2

Appendix B

DEVELOPMENT OF A DOUBLE MONOCHROMATOR FOR USE I N PRESENCE LIGHT COLOR EVALUATION STUDIES

P r i o r t o t h e s t a r t of t h i s c o n t r a c t HSRI had begun develop-

ment of a double monochromator f o r use i n some s t u d i e s concerned

wi th d r i v e r hue d i s c r i m i n a t i o n , This p r o j e c t was continued a s

p a r t of t h e o v e r a l l r e a r l i g h t i n g systems resea rch program though

it was given low p r i o r i t y .

On t h e b a s i s of s t u d i e s t h a t had been completed be fo re t h e

i n i t i a t i o n of t h e c o n t r a c t r e sea rch it became apparent t h a t t h e

use of more than one c o l o r on t h e r e a r l i g h t i n g system of v e h i c l e s

might be u s e f u l i n a i d i n g i n t h e d e t e c t i o n of s t o p and t u r n s i g -

n a l s . Color coding had been found t o be a u s e f u l means of provid-

i n g improved a l e r t i n g t o fol lowing-car d r i v e r s of t h e presence of

a s t o p o r t u r n s i g n a l , These f i n d i n g s were confirmed i n t h e s t u d i e s

conducted under t h i s r e sea rch program i n t h e Task-1 tests.

For t h i s reason it was cons idered impor tant t o o b t a i n some f u r t h e r

informat ion t h a t would enable s p e c i f i c a t i o n s t o be made f o r c o l o r

f i l t e r s i n a mul t i -color r e a r l i g h t i n g system,

P r i o r d a t a had a l ready shown t h a t v i s i b i l i t y of r ed and green-

b l u e of bandwidths s i m i l a r t o those found i n t r a f f i c s i g n a l con-

t r o l s were approximately t h e same, b u t t h e primary d isadvantage

of green-blue compared t o r e d was t h a t i t tended t o be confused

wi th whi te by co lo r -b l ind obse rve rs (Mortimer, 1969a) . I n a d d i t i o n ,

o t h e r work has i n d i c a t e d t h a t it may be u s e f u l t o incorpora te a

g r e a t e r p ropor t ion of l i g h t i n t h e yellow reg ion of t h e spectrum

f o r r e d vehicLe l i g h t s t o improve c o l o r cueing f o r co lo r -b l ind

d r i v e r s (Al len , 1966) . I t was, t h e r e f o r e , in tended t o develop a device a t minimum

c o s t which would permi t measurements t o be made of hue d i s c r i m i -

n a t i o n and c o l o r i d e n t i f i c a t i o n f o r both normal and p r i m a r i l y

co lo r -b l ind d r i v e r s i n o r d e r t h a t informat ion becomes a v a i l a b l e

f o r t h e s p e c i f i c a t i o n s f o r s i g n a l and presence l i g h t c o l o r f i l t e r s .

It was cons idered p a r t i c u l a r l y impor tant t o develop f i l t e r

wavelength d i s t r i b u t i o n s which would minimize t h e confus ions

among t h e d i f f e r e n t c o l o r s so a s t o maximize t h e i r coding po-

t e n t i a l .

No exper imenta l work was c a r r i e d o u t up t o t h i s t ime

s i n c e t h e e f f o r t has been used i n t h e development and con-

s t r u c t i o n of t h e dev ice which i s now almost completed.

DESCRIPTION OF DOUBLE MONOCHROMATOR. - - - - - -

The double monochromator i s composed of two s i n g l e mono-

chromators which o p e r a t e independently of each o t h e r and a r e

p laced such t h a t t h e o u t p u t of each i s focused on a ground g l a s s

sc reen w i t h t h e two images of approximately 3/16" x 1 / 2 inches

each being separa ted by about 1 / 4 i nches . The two monochromators

have a common p r o j e c t i o n lamp i n p u t t o reduce t h e e f f e c t s of

v o l t a g e v a r i a t i o n s and c o l o r changes. The o p t i c a l system i s

i d e n t i c a l f o r each and i s shown i n F igure B . 1 .

The lamp f i l a m e n t i s focused on t h e en t rance s l i t of each

Farrand No. 132106, Foci-Flex monochromator by a l e n s . I n t h i s

l i g h t p a t h a r e l o c a t e d an e l e c t r o m a g n e t i c a l l y o p e r a t a b l e s h u t t e r ,

a n e u t r a l d e n s i t y wedge and a n e u t r a l d e n s i t y f i l t e r . The s h u t t e r

i s opera ted by an e l e c t r i c a l so leno id . The wedge i s pos i t ioned

by means of a l ead screw opera ted from o u t s i d e t h e monochro-

mator enc losure . F i l t e r s may be removed o r r ep laced through

an opening i n t h e cover . (F igure B . 2 ) .

I n s i d e t h e Farrand monochromator t h e l i g h t is r e f l e c t e d

from a c o l l i m a t i n g m i r r o r on to t h e r e f l e c t i v e g r a t i n g . The

d i s p e r s e d beam i s d i r e c t e d onto t h e o t h e r c o l l i m a t i n g m i r r o r

and focused a t t h e e x i t s l i t s . The angu la r p o s i t i o n of t h e

g r a t i n g i s a d j u s t e d t o g i v e t h e d e s i r e d c o l o r a t t h e e x i t

s l i t . From t h e e x i t s l i t t h e beam i s focused on t h e ground

g l a s s sc reen . Both t h e e n t r a n c e and e x i t s l i t s may be changed t o produce d e s i r e d band widths from 2.5 t o 1 0 . 0

m i l l i m i c r o n s . The e n t i r e ins t rument i s enclosed w i t h i n a l i g h t - t i g h t

Lamp

eutral oensity Wedge

Farrand Monochromator

Entrance Slit

collimating Mirror

\d Observer's Eye Point

B.1 Ray path diagram in one line of double monochromator.

B.2 Double monochromator with power supply.

cover w i t h i n t e r n a l b a f f l e s t o p r e v e n t d i l u t i o n and mixing

of t h e l i g h t beams.

The monochromator i s s p e c i f i e d t o have a range of 215-800

~ n y , and has about 28,000 g r a t i n g l i n e s p e r inch . F igu re B-3.

shows t h e monochromator w i t h one of t h e s i d e c o v e r s removed.

The purpose of t h e s o l e n o i d ope ra t ed s h u t t e r s i s t o

enab le t h e c o l o r e d s t i m u l i t o be p re sen ted f o r predetermined

t ime p e r i o d s e i t h e r s imu l t aneous ly o r i n an a l t e r n a t i n g o r d e r ,

one s t i m u l u s a t a t ime . Th i s w i l l a l l o w c o n t r o l of s t i m u l u s

exposure t o t h e o b s e r v e r s and may a i d i n hue d i s c r i m i n a t i o n

and i d e n t i f i c a t i o n s t u d i e s .

Before d a t a c o l l e c t i o n may proceed it w i l l be neces sa ry

t h a t t h e d e v i c e be c a l i b r a t e d f o r s t i m u l u s i n t e n s i t y i n bo th

channe l s of t h e e q u i p e n t . Th i s w i l l be neces sa ry , a l s o , i n

o r d e r t o be a b l e t o c o n s t a n t l y monitor t h e l i g h t o u t p u t of t h e

p r o j e c t i o n lamp used t o p rov ide t h e l i g h t sou rce f o r bo th mono-

chromators . C a l i b r a t i o n of t h e n e u t r a l d e n s i t y f i l t e r s w i l l

a l s o be r e q u i r e d . When t h i s i s accomplished it would be

p o s s i b l e t o p r e s e n t s t i m u l i , e i t h e r s u c c e s s i v e l y a long one

channel o r i n bo th channe l s f o r comparison purposes , which

w i l l be matched i n b r i g h t n e s s over a r ange of i n t e n s i t y l e v e l s .

No s t u d i e s have been conducted w i t h t h e d e v i c e a t t h e

moment and some a d d i t i o n a l work i s r e q u i r e d a s a l r e a d y i n d i -

c a t e d i n o r d e r t o p l a c e it i n t o o p e r a t i o n a l c o n d i t i o n . I t

i s expec ted t h a t t h e d e v i c e may have c o n s i d e r a b l e u t i l i t y

i n g e n e r a l hue d i s c r i m i n a t i o n expe r imen ta t ion and p a r t i c u l a r l y

i n t h e d e f i n i t i o n of s i g n a l and presence lamp c o l o r f i l t e r

c h a r a c t e r i s t i c s .

B . 3 Double monochromator w i t h s i d e cover removed.

HIGHWAY SAFETY RESEARCH INSTITUTE . , I s Institute of Science and Technology I l l

, ' I 7 i i i Huron Parkway and Baxter Road

! ; / ._ J , - Ann Arbor, Michigan 48105

.... Phone: 764-4158 THE UNIVERSITY OF MICHIGAN

Appendix C-1

I n s t r u c t i o n s To Driver

1. This c a r i s on a s p e c i a l t e s t which r e q u i r e s t h e

use of some ins t rumenta t ion t h a t has been placed

i n t h e t runk.

P lease do n o t l eave t h i s v e h i c l e wi thout f i r s t

locking i t , and you should n o t su r render t h e keys

t o any o t h e r i n d i v i d u a l , e . g . , parking l o t a t t e n -

dan t s .

2 . When d r i v i n g t h i s c a r p lease be s u r e n o t t o r i d e

t h e brake peda l , and USE THE RIGHT FOOT ONLY FOR

BRAKING.

3. P lease FILL OUT THE ATTACHED TRIP SHEET BEFORE AND

AFTER EACH TRIP.

Thank you.

T R I P SHEET

T r i p

No.

N a m e of

D r i v e r

I 1 I

I

I

i

I

O d o m e t e r a t S t a r t of T r i p

I

-

- - -

L"---- - -

. . - - - - -

I_-

T i m e a t S t a r t of T r i p

- ,

- - -

1 I

A p p r o x i m a t e M i l e s D r i v e n i n :

O d o m e t e r a t End of T r i p

I

' C o u n t r y ; 'Speed L i m i t

,40 or A b o v e

C i t y -

L i m i t 4 0 or L e s s

t X-Way or

F r e e w a y

U s e this

Space for

C o n m I e n t s

T i m e a t End of Trip

D o Y o u

B r a k e W i t h R i g h t (R)

or- L e f t (L) Foot

Appendix C-2

PROGRAM DESCRIPTION OF COASTING SIGNAL

ANALYSIS MAGNETIC TAPE DATA PROCESSING SYSTEM

Objec t : To r e a d magnet ic d a t a t a p e s i n t o t h e hybr id com-

p u t e r system, and produce punched c a r d o u t p u t w i t h in fo rma t ion

on each c o a s t i n g e v e n t d e t e c t e d on t h e t a p e .

Equipment Used: Arnpex Model FR1900 7 Channel Tape Uni t

AD-4 Analog Computer

IBM 1130 D i g i t a l Computer

Program: The i n t e r f a c e diagram (F igure C - 1 ) shows t h e

flow of i n fo rma t ion from t h e magnet ic t a p e i n p u t t o t h e punched

ca rd ou tpu t . The t a p e i s read by t h e 7-channel u n i t , w i t h t h e

s i g n a l s from t h e seven channels f e d i n t o ana log computer t runk

l i n e s a s i n d i c a t e d . The s i g n a l s a r e processed by t h e ana log

program, t h e n s e n t t o t h e d i g i t a l . The t a p e i s gene ra t ed i n

t h e ins t rumented automobile a t 1 7/8 i nches / sec , and s e n t i n t o

t h e computer t h a t i s , times f a s t e r .

Program Logic: A f t e r t h e t a p e u n i t i s s t a r t e d , t h e 7 t runk - l i n e s a r e monitored by t h e ana log computer. I f v e h i c l e v e l o c i t y

was less t h a n 20 rnph ( i n c r e a s i n g ) o r less than 1 mph ( d e c r e a s i n g )

t h e d a t a sample e n a b l e l e v e l (channel 3 ) w i l l be low. When t h e

e n a b l e l e v e l i s low, a s t e a d y c a l i b r a t i o n s i g n a l i s g iven on

channel two. The c a l i b r a t i o n l e v e l a l t e r n a t e s from ground t o

0 .525 v o l t s (cor responding t o 30 rnph) each t i m e t h e enab le l e v e l

I AMPEX TAPE READSR I

C-2.1 Tape processing Interrace diagram for coasting signal analysis,

drops t o low. However, when t h e enab le s i g n a l i s h igh , v e l o c i t y

i s r ead on channel 2 , and t h e program moni tors channels 4 and 7

f o r a r e l e a s e p u l s e , A s soon a s a r e l e a s e p u l s e i s d e t e c t e d ,

t h e fo l lowing sequence t a k e s p l ace :

(1) t h e v e l o c i t y i s r ead

( 2 ) t ime p u l s e i n t e g r a t i o n commences

( 3 ) i n t e g r a t i o n of v e l o c i t y t o o b t a i n d i s t a n c e commences

( 4 ) channels 5 and 6 a r e monitored f o r an a p p l i c a t i o n p u l s e

A s soon a s an a p p l i c a t i o n p u l s e i s d e t e c t e d , t h e fo l lowing

sequence t a k e s p l a c e :

(1) t h e i n t e g r a t o r s measuring t ime and d i s t a n c e a r e p laced i n t o a ho ld c o n d i t i o n , a s i s t h e i n t e g r a - t o r t r a c k i n g v e l o c i t y

( 2 ) t i ~ n e , v e l o c i t y , and d i s t a n c e are r ead by t h e d i g i t a l computer

(3 ) i n t e g r a t o r s a r e p laced i n normal o p e r a t i n g c o n d i t i o n

( 4 ) channels 4 and 7 a r e monitored f o r a r e l e a s e p u l s e , s t a r t i n g t h e sequence aga in . A t a p p r o p r i a t e t imes , o u t p u t i s produced on punched c a r d s . D e t a i l s a r e d i s c u s s e d under D i g i t a l Program below

Analog Program: The ana log program produces cont inuous ,

d i s c r e t e and l o g i c d a t a t o t h e d i g i t a l computer. T i m e , v e l o c i t y ,

d i s t a n c e , c a l i b r a t i o n l e v e l , a c c e l e r a t i o n a p p l i c a t i o n , and brake

a p p l i c a t i o n ( t h e l a t t e r two s i g n a l s be ing t100V i f t r u e , 0 v o l t s

i f f a l s e ) a r e s e n t t o t h e d i g i t a l computer through h igh speed

a n a l o g / d i g i t a l convers ion channels . Logic s i g n a l s , i n c l u d i n g

t h e enab le s i g n a l , a c c e l e r a t o r r e l e a s e , b rake r e l e a s e , a c c e l e r a -

t o r a p p l i c a t i o n , and brake a p p l i c a t i o n s i g n a l s , a r e s e n t t o t h e

d i g i t a l over t h e sense l i n e s ( s e e i n t e r f a c e diagram). The

a p p l i c a t i o n and r e l e a s e pu l ses a r e of 1 p second d u r a t i o n , and

a r e s e n t upon d e t e c t i o n of a leading edge from any of t h e t ape

reader channels 4 through 7. A r e s t a r t pulse i n d i c a t i n g t h e

d i g i t a l computer has completed a coas t ing time measuring se-

quence, i s s e n t over a d i g i t a l c o n t r o l l i n e .

The analog computer c i r c u i t r y processes t h e information

from t h e t ape and c o n t r o l s and sequences t h e t o t a l program.

Included 1s c i r c u i t r y t o :

(1) d e t e c t leading edges of pu l ses

( 2 ) f i l t e r t h e v e l o c i t y and c a l i b r a t e s i g n a l s

( 3 ) shape t h e t iming pu l ses

( 4 ) c o n t r o l time and d i s t a n c e i n t e g r a t o r s and v e l o c i t y t r a c k i n g c i r c u i t

Provis ion i s made f o r running t h e program without t h e

d i g i t a l computer, wi th t h e ou tpu t appearing a s a continuous

s t r i p c h a r t recording. This mode of opera t ion i s used f o r pro-

gram checking, and has been very u s e f u l i n program debugging.

D i g i t a l Program:

COAST - This f o r t r a n program c a l l s on t h e Hybrid Communica-

t i o n Routines and r e c e i v e s t h e fol lowing information from t h e

Analog Computer:

a . Has t h e r e been a change i n t h e s t a t u s of t h e brake ( r e l e a s e / a p p l i c a t i o n ? )

b. Has t h e r e been a change i n t h e s t a t u s of t h e accel - e r a t o r ( r e l e a s e / a p p l i c a t i o n ? )

When a r e l e a s e occurs ( coas t ing begins) t h e d i g i t a l program reads

the initial celocity from the analog computer and then waits for

an applicaticn to occur. When an application occurs, the pro-

gram reads time, final velocity, and distance from the analog

computer. program also sets an INDEX which identifies the

event :

index = 2: accelerator release, accelerator application

index = 3: accelerator release, brake application

index = 4: brake release, accelerator application

index = 5: brake i-elease, brake application

The program then goes back to look for the next release. - .

The information recaived from the analog is stored in

cors, arid 2unched on cards during the time when the prcgra is

waiting for a release to occlll: (i.e., either the car is stopped

or else the accelerator is being applied, and no coasting is

taking ?lace) .

Each card or "point" consists of nine values, five of which

describn, an dccurrence of coasting, They are:

1, the "index" (Zefined above)

2. timz

3. hitial velocity

4, final veiocity

5. cietance '

The other four values represent the calibration signal,

which are used as a correction factor in datc analysis. This

signal is read four ti~es whenever the car is stopped, with a

' . d l second wait betwea each read. The next point wil.1 contsin

t h e i n i t i a l v e l o c i t y from t h e analog computer and then wa i t s f o r

an a p p l i c a t i o n t o occur. When an a p p l i c a t i o n occurs , t h e pro-

gram reads time, f i n a l v e l o c i t y , and d i s t a n c e from t h e analog

computer. The program a l s o sets an I N D E X which i d e n t i f i e s t h e

event ;

index = 2: a c c e l e r a t o r r e l e a s e , a c c e l e r a t o r a p p l i c a t i o n

index = 3: a c c e l e r a t o r r e l e a s e brake a p p l i c a t i o n

index = 4 : brake r e l e a s e , a c c e l e r a t o r a p p l i c a t i o n

index = 5: brake r e l e a s e , brake a p p l i c a t i o n

The program then goes back t o look f o r t h e next r e l e a s e .

The informat ion rece ived from t h e analog i s s t o r e d i n

co re , and punched on ca rds dur ing t h e time when t h e program i s

wa i t ing f o r a r e l e a s e t o occur ( i . e . , e i t h e r t h e c a r i s stopped

o r e l s e t h e a c c e l e r a t o r i s being app l i ed , and no coas t ing i s

t ak ing p l a c e ) .

Each card o r "po in t " c o n s i s t s of n ine va lues , f i v e of which

d e s c r i b e an occurrence of coas t ing . They a re :

1. t h e "index" (def ined above)

2 . t i m e

3. i n i t i a l v e l o c i t y

4 . f i n a l v e l o c i t y

5. d i s t a n c e

The o t h e r four va lues r e p r e s e n t t h e c a l i b r a t i o n s i g n a l ,

which a r e used a s a c o r r e c t i o n f a c t o r i n d a t a a n a l y s i s . This

s i g n a l i s read four t imes whenever t h e c a r i s stopped, wi th a

. 0 1 second w a i t between each read. The next p o i n t w i l l con ta in

these four values--for all other points, four zeroes are used

to indicate that no calibration values are present.

Numbers are punched in six-column fields consisting of

a sign and five digits, since this form requires the least

data conversion.

After a tape has been read and punched, the cards are

reprocessed, and the data, the tape identification number, and

a deck sequence number is punched on each card.

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Documents

Automotive Rear Lighting and Signaling Resea~h