SPEED LIMITS: planning perspectives SPEED LIMITS: planning perspectives and driversand drivers’’ attitudes in Greeceattitudes in Greece

Petros VythoulkasBasil Psarianos Pavlos Chorianopoulos

Faculty of Rural and Surveying EngineeringNational Technical University of Athens

Eva KasapiMinistry of Environment, Regional Planning and Public Works

11stst INTERNATIONAL SYMPOSIUM ONINTERNATIONAL SYMPOSIUM ONFREEWAY AND TOLLWAY OPERATIONSFREEWAY AND TOLLWAY OPERATIONS

TRB Freeway Operations Committee TRB Freeway Operations Committee Athens 2006Athens 2006

safety, environmental

andenergycosts

mobilityand

economiccosts

• Speed may affect the severity and risk of accidents. • But unreasonably low speed limits increase drivers’ violation

of the speed limits

Setting speed limits: a complex tradeSetting speed limits: a complex trade--offoff

speed

• Investigate drivers’ speed choice behaviour and their attitudes towards speed limits

• Review the current practices in setting speedlimits.

• Directions for future research

OObjectivesbjectives

DriversDrivers’’ speed choicespeed choice

Most drivers select a reasonably safe speed for the conditions under which they travel

They select their selfself--optimum speedoptimum speed primarily on the basis ofTravel time minimisationAccident risk minimisationMinimisation of the Risk of being caught speeding Fuel economy

The self-optimum speed is related to driver’s Personal characteristics age, income, driving experience, risk behaviour, environmental awarenessJourney characteristics

Speed choices are analysed based :

a) on actual speed data collected through the use of radarmeters at 15 stations along the rural highway network ofGreece.

b) on a dataset collected through a questionnaire surveythat was conducted at 5 motorway toll plazas in Greece.

Driver speeds in the trunk road network in GreeceDriver speeds in the trunk road network in Greece

Surveys in the context of the research project

“Method for Setting Reliable Speed Limits in Greece”funded by the Ministry of Environment, Regional Planning and Planning Works.

Motorway with local speed limit 90 km/hMotorway with local speed limit 90 km/h

probability distribution of observed speeds in motorway with speed limit 90 km/h

0%2%

8%

11%

7%

12% 12% 11%

7%5%

3% 2%0%

21%

0%

5%

10%

15%

20%

25%

85 90 95 100 105 110 115 120 125 130 135 140 145 150

observed speed

0%

20%

40%

60%

80%

100%

120%

histogram Cumulative Probability Distribution

V85 = 127 km/hSpeed limit

Probability distribution of observed speeds in Probability distribution of observed speeds in motorway section with local speed limit 90 km/hmotorway section with local speed limit 90 km/h

85%

1,5%

Motorway with general speed limit 120 km/hMotorway with general speed limit 120 km/h

Cumulative probability distribution of observed speeds in the left and right lane of motorway with speed limit 120 km/h

0%

20%

40%

60%

80%

100%

120%

90 100 110 120 130 140 150 160 170 180 190 200

Left laneRight laneboth lanes

140 152 157

5,6%

19,3%

31,7%

85%

Speed limit

Probability distribution of observed speeds in motorway Probability distribution of observed speeds in motorway with general speed limit 120 km/hwith general speed limit 120 km/h

Speed (km/h)

Roadside surveysRoadside surveys

• Self reported speed and relation to drivers’characteristics

• Drivers’ attitudes towards speed limits

Histogram and cumulative probabality distribution of self reported speeds in motorways with with speed limit 120 km/h

0% 1% 0%

5%

1% 1%

26%

3%1%

6%8%

29%

6%

12%

0%

5%

10%

15%

20%

25%

30%

35%

70 80 90 100 110 120 125 130 135 140 150 155 160 170 180 190 200 220

self reported speed (km/h)

0%

20%

40%

60%

80%

100%

120%

cum

ulat

ive

prob

abili

ty d

istri

butio

n

Histogram Cumulative probability distribution

V85 = 140 ~150 km/h

Self reported speeds in motorways with general Self reported speeds in motorways with general speed limit 120km/hspeed limit 120km/h

Distribution of self reported speed in motorways with speed limit 120 km/h by driver's age

18%

24%

42%

37%

34%

34%

14%

14%

15%

10% 11%

9%

23%

32%

25%

31%

25% 27

%

41%

46%

13%

5%

17%

11%

16%

24%

13%

0%

5%

10%

15%

20%

25%

30%

35%

40%

45%

50%

18 - 24 25 - 34 35 - 44 45 - 54 55 - 64 > 65 Sampledriver's age

= < 80 km/h 81 - 100 km/h 101 - 120 km/h121 - 130 km/h 131 - 140 km/h > = 141 km/h

Self reported speed and driverSelf reported speed and driver’’s age s age in motorways with general speed limit 120 km/hin motorways with general speed limit 120 km/h

Distribution of self reported speed in motorways with speed limit (120 km/h) by vehicle engine size

7%9%

7% 8%

50%

43%

29%26%

7%

34%

64%

25%

8%

17%20% 21%

0%

10%

20%

30%

40%

50%

60%

70%

<= 1100 1101 - 1400 1401 - 1800 1801 - 2300 > 2300 sample

= < 80 km/h 81 - 100 km/h 101 - 120 km/h121 - 130 km/h 131 - 140 km/h > = 141 km/h

Self reported speed and vehicle engineSelf reported speed and vehicle engine’’s power s power in motorways with general speed limit 120 km/hin motorways with general speed limit 120 km/h

Distribution of self reported speed in motorway and trip frequency

5%14%

3%

16%7%

20%

10%

42% 43% 41%49%

63%67%

46%53%

44%

57%

36%30%

13%

44%

0%

10%

20%

30%

40%

50%

60%

70%

80%

almostevery day

1 - 2 days/week

once in afortnight

once amonth

severaltimes a

year

1 - 3 timesa year

Sample

< 110 km/h 110 - 130 km/h > 130 km/h

Self reported speed and frequency of useSelf reported speed and frequency of usein motorways with general speed limit 120 km/hin motorways with general speed limit 120 km/h

Linear regression coefficientsCoef value t

(Constant) 109,94 13,19

AGE 18 - 24 29,961 5,22

AGE 25 - 34 27,864 5,85

AGE 35 - 44 19,266 4,04

AGE 45 - 54 21,596 4,56

AGE 55 - 64 20,229 4,10

ENGINE > 2300 cc 24,926 3,61

Frequency: Almost every day 6,593 1,82

GENDER -6,011 -1,93

Involvement in an accident -5,214 -1,95

Speeding ticket in the last 5 years 6,529 2,75

Safety is a reason for conforming with speed limit -11,127 -4,01

Relationship between self reported speed and personal Relationship between self reported speed and personal characteristics of drivers characteristics of drivers

Reference values:Reference values:

- Age > 65

- Engine =< 1100 cc

- Frequency 1- 3 /year

- Gender male

- Not involved in accident

- No speeding ticket

- Do not consider safety as a reason for conforming with speed limit

β Sig.

AGE 18 - 24 1,551 0,005

AGE 25 - 34 1,3 0

GENDER (0:male, 1:female) -0,826 0,033

ENGINE > 2300 cc 2,64 0,014

ENGINE 1801 – 2300 cc 0,946 0,014

ENGINE 1401 – 1800 cc 0,601 0,023

SPEEDING TICKET 0,967 0,001

SAFETY is a reason for conforming with the speed limit -1,002 0

Exceeding the motorway speed limit:Exceeding the motorway speed limit:Factors affecting driver choices Factors affecting driver choices

Binary Binary logitlogit coefficientscoefficients

Reasons that car drivers conform with the Reasons that car drivers conform with the motorway general speed limit (motorway general speed limit (120km/h120km/h))

Driver’s speedReasons for conforming with speed limit

% of drivers

Drivers who Conform with speed limit

Others F sig

Safety 76,2% 128 142 23,4 0

Risk of getting a speeding ticket 25,5% 130 136 4,929 0,02

Legislation 14,3% 131 131 0,005 0,94

Fuel cost 4,4% 127 131 0,573 0,45

Driver is not in a hurry 4,1% 121 132 3,059 0,81

Environmental 1,4% 122 131 0,695 0,40

Other reasons 1,4% 127 131 0,128 0,72

Drivers who stated that they do not conform with the 120km/h speed limit in motorways 3,4% 160 130 20,26 0

Reasons for exceeding the speed limit

% of drivers

Enjoy speeding 4,8% 149 130 10,1 0,00

Drivers who exceed the speed limit

Others F sig.

Being in a hurry 42,9% 131 131 0,01 0,91

The limit for safe driving is higher than 120km/h in motorways 31,3% 138 128 13,1 0

Other reasons 24,5% 134 131 0,36 0,55

Adjusting to the speed of other vehicles 5,1% 132 131 0,02 0,89

Being bored driving at low speed 4,8% 147 131 8,1 0,01

No specific reason 3,4% 133 131 0,11 0,74

Never/rarely exceed the speed limit 24,5% 116 136 56,5 0

Reasons that drivers exceed the motorway general Reasons that drivers exceed the motorway general speed limit (speed limit (120km/h120km/h))

DriversDrivers’’ views on the views on the 120km/h120km/h general speed limit on general speed limit on motorways motorways

Drivers' views on the level of speed limit in motorways (120km/h)

65%

31%

5%

120

138

112

0%

10%

20%

30%

40%

50%

60%

70%

It's very high andshould be decreased

It's about right It's very low andshould be increased

% o

f driv

ers

100

110

120

130

140

150

mea

n sp

eed

(km

/h)

Speed limits should never be exceeded

8%

42%

10%

35%

5%

126

139

152

131

114

0%

5%

10%

15%

20%

25%

30%

35%

40%

45%

StronglyAgree

Agree Neitheragree notdisagree

Disagree StronglyDisagree

%D

river

s

110

120

130

140

150

160

mea

n sp

eed

(km

/h)

Should drivers exceed speed limits?Should drivers exceed speed limits?

Speed limits should never be Speed limits should never be exceededexceeded

Speed limits are lower than the speed limit for safe driving, and thus they could be exceeded by 10 km/h or more

2%

36%

14%

46%

2%

151

137

124

100

138

0%

10%

20%

30%

40%

50%

60%

StronglyAgree

Agree Neither agreenot disagree

Disagree StronglyDisagree

% o

f Driv

ers

90

100

110

120

130

140

150

160

mea

n sp

eed

(km

/h)

Should drivers exceed speed limits?Should drivers exceed speed limits?

Current Speed limits are lower than the limit Current Speed limits are lower than the limit for safe driving and thus could be exceeded for safe driving and thus could be exceeded

by 10 km/h or even more by 10 km/h or even more

Speed limits are inaccurateDrivers can judge whether they can drive slowly or fast .

9%

59%

12%18%

2%

150

134130

123

137

0%

10%

20%

30%

40%

50%

60%

70%

StronglyAgree

Agree Neither agreenot disagree

Disagree StronglyDisagree

% o

f driv

ers

110

120

130

140

150

160

mea

n sp

eed

(km

/h)

Should drivers exceed speed limits?Should drivers exceed speed limits?

Speed limits are inaccurate Speed limits are inaccurate Drivers can judge for themselves whether Drivers can judge for themselves whether

they should drive slowly or fastthey should drive slowly or fast

Main findings from surveysMain findings from surveys

Current speed limits are exceeded by the vast majority of drivers.

Speed limit offenders are mostly Young drivers, Frequent users and drivers of high engine power cars.

Safety is the main reason for conforming with speed limits.

Being in a hurry is the main reason for exceeding speed limits.

~40% of drivers consider current speed limits as lower than the limit for safe driving, and believe that speed limits could be exceeded by 10km/h or more.

Self optimum speed :Self optimum speed :

Social optimumSocial optimumCost of travel time

Accident costs

Environmental costs

Energy costs

Enforcement cost

drivers can impose significant risks drivers can impose significant risks and uncompensated costs on othersand uncompensated costs on othersDifferent drivers have different risk Different drivers have different risk tolerancestolerancesMay have inadequate information May have inadequate information and/or misjudge roadway conditions, and/or misjudge roadway conditions, and own and vehicle capabilitiesand own and vehicle capabilitiesMay misjudge the effect speed on May misjudge the effect speed on accident probability and severity accident probability and severity

Reasons for regulating driversReasons for regulating drivers’’ speedspeed

Driver tries to minimise travel time, perceived risk of accident perceived risk of being caughtfuel cost

Different approaches in setting speed limitsDifferent approaches in setting speed limits(Fildes et al. for Austroads 2005)

Engineering Engineering Road geometry, Traffic speeds, Accident data, Traffic volumes, Roadside development.

DriversDrivers’’ ChoiceChoiceDrivers select a reasonable and safe travel speed.The posted speed limit is the 85th percentile driving speed.

Economic OptimisationEconomic OptimisationAll costs (travel time, injury, death, environmental, energy) associated with travel are expressed in monetary terms.The posted speed limit is the speed that results in the lowest cost.

Harm MinimisationHarm MinimisationLife and health cannot be measured in monetary terms. Fatalities or serious casualties is not considered as an inevitable cost of increased mobility.

Economic optimisation approachEconomic optimisation approach(EU-MASTER, Cameron)

Explicit framework that takes account of :

• Road accident costs AccC

• Travel time costs TimC

• Vehicle operating costs OpC

• Traffic emissions costs EmisC

• Noise pollution costs NoisC

Road accident costsRoad accident costs

AccC = Σi NiA * VAcci

where

NA the number of accidents of category i Vacc the cost of an accident

Estimation of a fatal accident cost is a controversial issueDifferent methods

Human Capital ApproachWillingness to Pay

can lead to significantly different costs of accidents

The number of Road accidents The number of Road accidents (Nilsson (1984)(Nilsson (1984)

NA = (VA/VB)p * NB

NA = number of accidents After the speed change

VA = mean or median speed After

NB = number of accidents Before the speed change

VB = mean or median speed Before

p = 4 for fatal accidents 3 for serious injury accidents2 for minor injury accidents

Poor estimates of NB can result in highly inaccurate estimates of NA, particularly in the case of fatal accidents where p = 4

Speed variance is also considered as an important factor

Travel time costsTravel time costs

TimC = Traffic Volume * Travel Time * VoTrequires reliable estimates of the value of time

Vehicle operating costsVehicle operating costs

OpC = Traffic Volume * distance* Fuel Consumption * fuel cost

- Reliable Fuel consumption functions are available for differenttypes of vehicles

- Fleet composition data should be available

Traffic emissions costsTraffic emissions costs

• Hydrocarbons and other organic compounds (VOC), benzene, 1,3-butadiene

• Carbon monoxide CO• Nitrogen Oxides NOx• Particular Matter (PM) –

particles emitted from the exhaust

• CO2: is a main contributor to global warming.

Atmospheric emission pollutants which are normally regarded as the ones of most concern include:

0,0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0 20 40 60 80 100 120 140 160 180

speed (km/h))

ΝΟ

x em

issi

ons

(gr/k

m)

Euro III_< 1.4 l Euro III_1.4 - 2.0 l Euro III_> 2.0 l

Euro IV_< 1.4 l Euro IV_1.4 - 2.0 l Euro IV_> 2.0 l

NOx emissions rates

0 20 40 60 80 100 120 140 160 180Speed (km/h)

Extensive database of vehicle Emission functions is provided by the UK Dept of Environment

Traffic emissions costsTraffic emissions costs

EmisC = Σi Volume Pollutanti * CoPi

where CoPi the cost of pollutant i.

Traffic emission impact depends on • the size of the population living in the vicinity of the

road, and who are exposed to emissions, and • the emission concentration which the population is

exposed to.

Pollutant concentrations at the road side receptors should be estimated by taking into account the dispersion and dilution of the pollutants.

Vehicle fleet compositionCost of different pollutants has not been estimated in Greece

Noise pollution impactNoise pollution impact

Depends on the size of the population living in the vicinity of the road, and who are exposed to noise.

Noise level depends on speed, traffic volume and form of roadside development - Estimation of noise level is a complex problem often requiring specialised SW

Cost and effectiveness of noise barriers should be compared to cost of reduced mobility due to speed reduction

Cost of noise pollution – hedonic pricing applied in urban areas, WTP approaches

Noise pollution cost has not been estimated in Greece

All relationships for estimating safety, environmental, energy and mobility implications are based on driver speeds - not speed limits.

Nonlinear relationships imply that speed distributions rather than mean speed values should be used.

f( E[v] ) ≠ E[ f(v) ]Accident frequency is related to speed variance.

Intensity of speed enforcement affects speed distribution

But cost of intensive enforcement can incur high costs Speed limit

Speed limits, speed distribution and Speed limits, speed distribution and speed enforcementspeed enforcement

Low/moderate enforcement

Intense enforcement

Further research in• Effect of level of enforcement on speed distribution• Speed – accident relationships• Reliable estimates of accident, pollution costs

Future researchFuture research

Complexities and uncertainties related to the estimation of the monetary values of the various benefits and disbenefits from speed changes dictate that alternative options that could improve accident rate should always be considered before proceeding to speed limit changes.