TRAFFIC ENGINEERING COURSE

(PWE 8322)

ROUNDABOUTS

Instructor: Usama Elrawy Shahdah, PhDLecture # 05

Conflict Points2

Conflict points3

Geometric Characteristics

Entry width

Inscribed

circle

diameter

Exit width

Splitter island width

Circulatory roadway width

Geometric Characteristics5

6

7

Number of Lanes8

vc

va

Roundabout Volumes

Turning

movements

Roundabout

volumes

Steps

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

passenger car equivalents (pce)

Step 2: PHF volume adjustment

Step 3: Entry volume

Step 4: Exit volume

Step 5: Circulating volume

Entry Volume

Entry volume = sum of entering turning movements

Exit Volume

Exit volume = sum of turning movements as shown

Circulating Volume

Circulating volume = sum of turning movements as

shown

Example: Volume Conversion

Turning

movements

Roundabout

volumes

110350140

50240100

North/south:

4% SU trucks/buses, 2%

combo trucks

East/west:

2% SU trucks/ buses

?

PHF = 0.94

Example Step 1: PCE Calculation

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

% SU/bus (0.04) 1.5 pce/veh = 0.06

% combo (0.02) 2.0 pce/veh = 0.04

fhv = 1.04

530 veh

551 pceVehicle Type

Passenger CarEquivalent (pce)

Car 1.0

Single-unit truck or bus 1.5

Truck with trailer 2.0

Bicycle or motorcycle 0.5

Example Step 1: Completed PCE

Calculation

Raw Counts PCEs

110350140

50240100 111

354141

51242101

Example Step 2: PHF Factor

PCEs (hourly)PCEs (peak 15

minutes)

118377150

54258107111

354141

51242101

141 / 0.94 = 150

Example Step 3: Calculate Entry

Volume

Entry volume = sum of entering turning movements

118377150

54258107 645

?

? 419

?

64

2

79

7

Example Step 4: Calculate Exit Volume

Exit volume = sum of turning movements as shown

645

?

? 419

?

64

2

79

7

118377150

54258107

Example Step 5: Calculate Circulating

Volume

Circulating volume = sum of turning movements as

shown

645

628

82

6

419

453

64

2

79

7

118377150

54258107

Example: Solution

Turning

movements

Roundabout

volumes

110350140

50240100

North/south:

4% SU trucks/buses, 2%

combo trucks

East/west:

2% SU trucks/ buses

645

628

82

6

419

453

64

2

79

7

PHF = 0.94

22

Capacity Determination

HCM 2000 Method

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sssooollluuutttiiiooonnn

444...111 222...666

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444...666 333...111

)3600/(

)3600/(

1 fc

cc

tv

tv

cae

evc

vc

va

HCM method24

CONTROL DELAY & LOS25

Kimber Method26

Qe (capacity of entry flow) is linearly dependent

upon circulating flow crossing the entry (Qc).

Kimber Method27

Factors affecting the capacity of a roundabout:

Inscribed circle diameter D (m)

width of flare of each entry. e (m),

Approach width v (m)

effective length over which flare is developed l' (m)

entry angle (φ)

entry radius (r) (m)

Kimber Method28

Kimber Method29

Range of geometric variables in data set used by

Kimber to develop capacity expression

Kimber Method (simplified method)30

Single-lane roundabouts

This constraint implies that the capacity of the

circulating roadway of the roundabout is 1800 pcph.

Kimber Method (simplified method)31

Two lane roundabouts

Example32

A single-lane roundabout having the following geometric characteristics:

e = 4 m

v = 4 m

l’ = 40 m

r = 20 m

Φ = 30 degrees

D = 40 m

circulating volume = 285 pcph

the entry leg demand = 315 pcph.

Compute the average delay

Use an analysis period of 15 minutes.

Solution33

Use Simplified Kimber method

Delay

Trafficware Synchro34

Demonstrated in Class

Home Reading35

Synchro Studio 9 User Guide

NCHRPREPORT 672 “Design Roundabouts: An

Informational Guide”, Second Edition

36

Thanks for your time