CEE 495.001 – Spring 2005 Lectures 12 to 13 (Chapters 23) Analyses of Unsignalized Intersections

CEE 495.001 – Spring 2005CEE 495.001 – Spring 2005

Lectures 12 to 13Lectures 12 to 13

(Chapters 23)(Chapters 23)

Analyses of Unsignalized Analyses of Unsignalized IntersectionsIntersections


Types of Unsignalized Intersections Types of Unsignalized Intersections

UncontrolledUncontrolled Stop Sign ControlledStop Sign Controlled

TWSCTWSC AWSCAWSC

Yield Sign ControlledYield Sign Controlled RoundaboutRoundabout


TWSC Intersections TWSC Intersections

Priority movementsPriority movements


Gap Acceptance Gap Acceptance

Critical gap, tCritical gap, tcc

Minimum gap in the major stream that a minor street driver can acceptMinimum gap in the major stream that a minor street driver can accept Cannot be measured directly in the fieldCannot be measured directly in the field Drivers behave differentlyDrivers behave differently

Follow-up time, tFollow-up time, tff

Minimum headway between two consecutive vehicles in the minor streamMinimum headway between two consecutive vehicles in the minor stream Can be measured directly in the fieldCan be measured directly in the field

Veh1 Veh2tf

tmv


ttcc and t and tff

LTcTcGHVcHVcbc ttGtPttt 3

HVfHVfbf Pttt

MovementMovement

ttcbcb, sec, sec

ttfbfb, sec, secTwo-lane Two-lane Major StreetMajor Street

Four-lane Four-lane Major StreetMajor Street

Major LTMajor LT

Minor RTMinor RT

Minor THMinor TH

Minor LTMinor LT

4.14.1

6.26.2

6.56.5

7.17.1

4.14.1

6.96.9

6.56.5

7.57.5

2.22.2

3.33.3

4.04.0

3.53.5


Adjustments on tAdjustments on tcc and t and tff

LTcTcGHVcHVcbc ttGtPttt 3

HVfHVfbf Pttt

AdjustmentAdjustment ValuesValues

ttcHVcHV 1.0, Two-lane major street1.0, Two-lane major street

2.0, Four-lane major street2.0, Four-lane major street

ttcGcG 0.1, Movements 9 and 120.1, Movements 9 and 12

0.2, Movements 7, 8, 10 and 110.2, Movements 7, 8, 10 and 11

1.0, Otherwise1.0, Otherwise

ttcTcT 1.0, With two stage process1.0, With two stage process

0.0, With single stage process0.0, With single stage process

tt3LT3LT 0.7, Minor-street LT at T-intersection0.7, Minor-street LT at T-intersection

0.0, Otherwise0.0, Otherwise

ttfHVfHV 0.9, Two-lane major street0.9, Two-lane major street

1.0, Four-lane major street1.0, Four-lane major street


CapacityCapacity

Conflicting volume, vConflicting volume, vcxcx Figure 23.3 (page 670)Figure 23.3 (page 670)

Potential capacity, cPotential capacity, cpxpx

Movement capacity, cMovement capacity, cmxmx

)3600/(

)3600/(

1 fxcx

cxcx

tv

tv

cxpxe

evc

pxxmx cfc

7,4,07 pppf For minor street LT at T intersection


Delay and LOSDelay and LOS

5450

))(3600(

)1()1(9003600 2

T

c

v

c

c

v

c

vT

cd mx

x

mx

mx

x

mx

x

mxx

LOSLOS Average Control Delay, Average Control Delay, sec/vehsec/veh

AA

BB

CC

DD

EE

FF

0-10 0-10 (0-10)(0-10)

>10-15 >10-15 (10-20)(10-20)

>15-25 >15-25 (20-35)(20-35)

>25-35 >25-35 (35-55)(35-55)

>35-50 >35-50 (55-80)(55-80)

>50 >50 (>80)(>80)

* (xx ) for signalized intersections


ExerciseExercise

Using HCS to solve the sample problem given. After the model is set up, try to answer the Using HCS to solve the sample problem given. After the model is set up, try to answer the following questions.following questions.

1.1. Can you duplicate the results given in the example?Can you duplicate the results given in the example?

2.2. How many minor movements are involved in the example?How many minor movements are involved in the example?

3.3. Which minor movements have the same potential capacity and movement capacity, i.e., Which minor movements have the same potential capacity and movement capacity, i.e., which minor movements are not impeded by higher priority minor movements?which minor movements are not impeded by higher priority minor movements?

4.4. What is the basic critical gap and final critical gap for the minor street LT movement?What is the basic critical gap and final critical gap for the minor street LT movement?

5.5. What is the conflicting flow rate for minor street LT movement? Verify the result manually.What is the conflicting flow rate for minor street LT movement? Verify the result manually.

6.6. What is the probability of major street LT movement not blocking the minor street LT What is the probability of major street LT movement not blocking the minor street LT movement (i.e., probability of queue free for major street LT movement)?movement (i.e., probability of queue free for major street LT movement)?

7.7. what is the impedance factor for minor street LT movement? How is this factor used for the what is the impedance factor for minor street LT movement? How is this factor used for the calculation?calculation?

8.8. What are the movement capacities for the minor street LT and RT movements? What are the movement capacities for the minor street LT and RT movements?

9.9. What is the capacity for the minor street approach (shared LT and RT lane)What is the capacity for the minor street approach (shared LT and RT lane)

10.10. What is the control delay for the minor street approach? What is the control delay for the minor street approach?


ComplexitiesComplexities

* Upstream Signal Effect* Upstream Signal Effect

Two-stage crossingTwo-stage crossing

Flared approachFlared approach


RoundaboutRoundabout

Roundabout is a special type of Roundabout is a special type of traffic circletraffic circle Major differences between roundabout and traffic circleMajor differences between roundabout and traffic circle

SpeedSpeed Traffic controlTraffic control Priority of circulating trafficPriority of circulating traffic Design vehicleDesign vehicle Pedestrian accessPedestrian access ParkingParking Direction of circulationDirection of circulation

Types of roundaboutTypes of roundabout MiniMini Urban: compact, single-lane, double-laneUrban: compact, single-lane, double-lane Rural: single-lane, double-laneRural: single-lane, double-lane


Roundabout Design ElementsRoundabout Design Elements

Entry widthEntry width

Inscribed Inscribed circle circle diameterdiameter

Exit widthExit width

Splitter island widthSplitter island width

Circulatory roadway widthCirculatory roadway width


Roundabout Operations - HCMRoundabout Operations - HCM

Roundabouts introduced in 1997 HCMRoundabouts introduced in 1997 HCM Method unchanged in HCM 2000Method unchanged in HCM 2000 Uses analytical methodUses analytical method Only estimates capacity; no guidance on delay or level of serviceOnly estimates capacity; no guidance on delay or level of service Measured in PCEMeasured in PCE

)3600/(

)3600/(

1 fc

cc

tv

tv

cae

evc


FHWA MethodFHWA Method

Consideration of vehicle types (cars, trucks, motorcycles) Consideration of vehicle types (cars, trucks, motorcycles) Empirical regression modelEmpirical regression model Delay and LOSDelay and LOS

vc

va

http://www.tfhrc.gov/safety/00068.pdf


FHWA Method vs. HCMFHWA Method vs. HCM

Approach Capacity

200 400 600 800 1000 1200

Circulating Flow (pce/h)

Lower Bound

0

0

500

1000

1500

Upper Bound

Ent

ry C

apa

city

(pc

e/h)

Approach Capacity

200 400 600 800 1000 1200

Circulating Flow (pce/h)

Lower Bound

0

0

500

1000

1500

Upper Bound

Ent

ry C

apa

city

(pc

e/h)

FHWA

HCM


Steps to Calculate Roundabout VolumesSteps to Calculate Roundabout Volumes

Turning Turning movementsmovements

Roundabout Roundabout volumesvolumes


StepsSteps

Vehicle TypePassenger Car

Equivalent (pce)

Car 1.0

Single-unit truck or bus 1.5

Truck with trailer 2.0

Bicycle or motorcycle 0.5

Step 1: Convert trucks and other vehicle types to Step 1: Convert trucks and other vehicle types to passenger car passenger car equivalents (pce)equivalents (pce)

Step 2: PHF volume adjustmentStep 2: PHF volume adjustment Step 3: Entry volumeStep 3: Entry volume Step 4: Exit volumeStep 4: Exit volume Step 5: Circulating volumeStep 5: Circulating volume


Entry VolumeEntry Volume

Entry volume = sum of entering turning movementsEntry volume = sum of entering turning movements


Exit VolumeExit Volume

Exit volume = sum of turning movements as shownExit volume = sum of turning movements as shown


Circulating VolumeCirculating Volume

Circulating volume = sum of turning movements as shownCirculating volume = sum of turning movements as shown


Example: Volume ConversionExample: Volume Conversion



110110350350140140

5050240240100100

8080

410

410

9090

7070

530

530

120

120

North/south:North/south:4% SU trucks/buses, 2% 4% SU trucks/buses, 2%

combo truckscombo trucks

East/west:East/west:2% SU trucks/ 2% SU trucks/

busesbuses

??

PHF = 0.94PHF = 0.94


Example Step 1: PCE CalculationExample Step 1: PCE Calculation

SB TH: 530 veh (4% SU/bus, 2% combo)SB TH: 530 veh (4% SU/bus, 2% combo)% cars (0.94) % cars (0.94) 1.0 pce/veh 1.0 pce/veh ==

0.940.94

% SU/bus (0.04) % SU/bus (0.04) 1.5 pce/veh 1.5 pce/veh ==0.060.06

% combo (0.02) % combo (0.02) 2.0 pce/veh 2.0 pce/veh ==0.040.04

ffhvhv ==

1.041.04

530 veh530 veh

551 pce551 pce


Equivalent (pce)

Car 1.0





Equivalent (pce)

Car 1.0





Example Step 1: Completed PCE Example Step 1: Completed PCE CalculationCalculation

Raw CountsRaw Counts PCEsPCEs

110110350350140140

5050240240100100

8080

410

410

9090

7070

530

530

120

120

111111354354141141

5151242242101101

8383

426

426

9494

7373

551

551

125

125


Example Step 2: PHF FactorExample Step 2: PHF Factor

PCEs (hourly)PCEs (hourly) PCEs (peak 15 PCEs (peak 15 minutes)minutes)

118118377377150150

5454258258107107

8888

454

454

100

100

7878

586

586

133

133

111111354354141141

5151242242101101

8383

426

426

9494

7373

551

551

125

125

141 / 0.94 = 150141 / 0.94 = 150


Example Step 3: Calculate Entry Example Step 3: Calculate Entry VolumeVolume

Entry volume = sum of entering turning movementsEntry volume = sum of entering turning movements

118118377377150150

5454258258107107

8888

454

454

100

100

7878

586

586

133

133

645645??

??

??

????

??

419419

??

642

642

??

797

797


Example Step 4: Calculate Exit VolumeExample Step 4: Calculate Exit Volume

Exit volume = sum of turning movements as shownExit volume = sum of turning movements as shown

645645

610610

626626

??

??424424

??

419419

??

642

642

843843

797

797

118118377377150150

5454258258107107

8888

454

454

100

100

7878

586

586

133

133


Example Step 5: Calculate Circulating Example Step 5: Calculate Circulating VolumeVolume

Circulating volume = sum of turning movements as shownCirculating volume = sum of turning movements as shown

645645

610610

626626

628628

826

826

424424

660

660

419419

453453

642

642

843843

797

797

118118377377150150

5454258258107107

8888

454

454

100

100

7878

586

586

133

133


Example: SolutionExample: Solution



110110350350140140

5050240240100100

8080

410

410

9090

7070

530

530

120

120

North/south:North/south:4% SU trucks/buses, 2% 4% SU trucks/buses, 2%

combo truckscombo trucks

East/west:East/west:2% SU trucks/ 2% SU trucks/

busesbuses

645645

610610

626626

628628

826

826

424424

660

660

419419

453453

642

642

843843

797

797

PHF = 0.94PHF = 0.94


Example: Capacity CalculationExample: Capacity Calculation


Roundabout Roundabout category?category?

??645645

610610

626626

628628

826

826

424424

660

660

419419

453453

642

642

843843

797

797


Example: Capacity CalculationExample: Capacity Calculation

645645

826

826424424

Check capacity Check capacity of each entryof each entry


Example: Capacity checkExample: Capacity check

0

200

400

600

800

1000

1200

1400

0 400 800 1200 1600 2000 2400Circulatory Flow (veh/h)

Maxim

um

En

try F

low

(veh

/h)

Entering and circulating flow = 1800 veh/h

826826

607607

762762

Urban & Rural Single-

Lane Roundabouts

Urban Compact

Roundabouts


Example: Capacity CheckExample: Capacity Check

Entering volume = 645 pce/hEntering volume = 645 pce/h Capacity of entry:Capacity of entry:

Single-lane: 762 pce/hSingle-lane: 762 pce/h Urban compact: 607 pce/hUrban compact: 607 pce/h

Volume-to-capacity ratio:Volume-to-capacity ratio: Single-lane:Single-lane: 645 / 762 = 0.85645 / 762 = 0.85 ATAT Urban compact:Urban compact: 645 / 607 = 1.06645 / 607 = 1.06 OVEROVER

What to do when v/c >1.0?What to do when v/c >1.0? Repeat calculation for other approachesRepeat calculation for other approaches

What to do What to do

when v/c >1.0?when v/c >1.0?


Solution: Capacity CalculationSolution: Capacity Calculation

Urban CompactUrban Compact Single-LaneSingle-Lane

1.061.060.570.57

0.85

0.85

0.90

0.90

0.850.850.490.49

0.74

0.74

0.83

0.83

OVER OVER CAPACITYCAPACITY

OK OK (TODAY)(TODAY)


DelayDelay

Control delayControl delay Includes initial deceleration delay, queue move-up Includes initial deceleration delay, queue move-up

time, stopped delay, and final acceleration delaytime, stopped delay, and final acceleration delay Geometric delayGeometric delay

Delay experienced by a single vehicle with no Delay experienced by a single vehicle with no conflicting flowsconflicting flows

Caused by geometric featuresCaused by geometric features Total delay = Control + GeometricTotal delay = Control + Geometric Typical measure used: control delayTypical measure used: control delay

Documents

CEE 495.001 – Spring 2005 Lectures 12 to 13 (Chapters 23) Analyses of Unsignalized Intersections