1

TNK062 – Traffic modelingIntersections and traffic signals

» Johan Janson Olstam» Office: SP7206» E-mail: johja@itn.liu.se» Phone: 36 34 90 or

013 – 20 41 82 (VTI)

2

Contents

» 3 Lectures» 1 Computer exercise (incl. a Dugga)» 1 Assignment consisting of three parts

- Theory questions (Individually)- Calculation problems (Individually)- Task to be solved using CAPCAL

(groups of 2 students)

3

Basic principle

Eliminate primary conflicts by

» Separation in time» Separation in space

Primary conflictSecondary conflict

4

Different types of intersections

» Right of way» Stop or yield» Traffic signal» Roundabout» Freeway intersection

» Space or time separation?

Small intersections

Large intersections

5

One way to choose type

6

Quality-of-Service measures

» Capacity, K (C in eng litt.)» Degree of saturation, B (x in eng litt)» Queue lentgh (number of vehicles)» Delay (Interaction & geometric), d» Service time, b» Number of delayed or stopped vehicles

qB

K=

7

Saturation flow, s» max queue discharging rate when queue

discharging is possible (e.g. during green)» Measured in vehicles/h and are usually

defined per lane» veh/h/lane for an

undisturbed road» Depends on the intersection geometry» Compare with capacity – max number of

veh/h that can pass a point per time unit

1800 2000s ≈ −

8

Time gap – Time headway

Time gap

Time headway

9

Quality-of-service calculations for non-signalized intersections

Two different approaches

» Macro e.g.

» Micro critical time gaps

1mm

qK Kq

⎛ ⎞= −⎜ ⎟

⎝ ⎠

10

Micro models

no vehicle can pass1 vehicle can pass2 vehicles can pass

1

1 2

2 3

h TT h TT h T

<< << <

h

11

Critical time gaps» Base values (10% heavy vehicles)

» Follow-up time ~60% of the critical time gap

12

Capacity» Depends on supply and frequency of time gaps

» Number of time gaps average number of vehicles that can be discharged/time gap

» is the probability for time gaps that can be used by vehicles

≅

1k

kK q kp

∞

=

= ⋅∑ kp

k

13

Queue theory

A minor approach can be seen as a queue system characterized by

» distribution of the arrivals» distribution of service times» number of service stations» Queue discipline (FCFS = FIFO)

14

Time gap distributions

» Off-peak hours: all vehicles free time gaps exponential distributed

» Min time gap 0 shifted exponential distributed

» Vehicle platoons with fixed min time gap M3-distribution

→≠ →

→

15

Example - time gap distributions

0 5 10 15 20 25 300

0.05

0.1

0.15

0.2

0.25

time [s]

prob

abili

ty

M3-distExp-distExp-dist shifted

min 2 s500 vehicles/h1 7.2 s

tq

tq

==

= =

16

Minor stream Major flow

Minor stream Major flow

17

The coordinate transformation technique

18

Calculation of Quality-of-service

» Calculation of major flow» Calculation of critical time gap» Calculation of service times» Lane utilization» Correction for short lanes» Calculation of measures» Unprotected road users

19

Geometry and regulation

» Number of approach and exit lanes» Lane markings» Sight conditions» Pedestrian crossings» Speed limits» Stop or yield

20

Capcal

» Stands for CAPacity CALculation» Calculation of quality-of-service in stop, yield,

or signal intersections and roundabouts» Micro model» Static and deterministic» Used by municipalities, consultants, road

administration, etc

21 22

23

Other models» SIDRA http://www.sidrasolutions.com/» OSCADY/PICADY/ARCADY

http://www.trlsoftware.co.uk/products/products.asp?c=1&pid=15

» HCM-based models like HCS & HICAP http://mctrans.ce.ufl.edu/hcs/ and http://www.hicap2000.com/

» LISA+ http://www.schlothauer.de/en/» AMPEL/KREISEL/KNOBEL http://www.bps-

verkehr.de/index.html

24

Traffic signals

25

Advantages with traffic signals

» Allocate capacity amongst approaches and road user groups

» Create regularity and minimize waiting time» Give priority for buses, platoons,

emergency vehicles, etc» Traffic safety (also a disadvantage!)

26

Definitions

» Signal picture – Green, Amber, Red, Red-Amber, etc.

» Signal group – Signals that always are given r.o.w. (green) simultaneously

» Phase or stage – Combination of signal groups that are given r.o.w. at the same time

27

cycle time

red time green time amber

safety time red-amber

Road 1

Road 2

Road 1

Road 2

28

Effective green

, saturation flows

Red RA Green A Red

effective green

29

Phase- and signal group control

Phase technique

Signal grouptechnique

30

Control strategies

» Fixed-time – fixed green times/splits for each phase/signal group. Different schemes for different times of the day (peak/off peak)

» Vehicle actuated – changes between phases/signal groups are based on the present traffic conditions

31

Isolated/Coordinated

» Isolated intersection control – each traffic signal works independently, i.e. no coordination with other intersections.

» Coordinated signals – the control of one intersection affects and is affected of the control in other intersections

32

Classification of strategies

SPOT, TUCMaxbandTransyt

Coordinated

Green time extension, LHOVRA

Isolated

ActuatedFixed-time

33

Bus priority

YESYESCoordinated

YESNOIsolated

ActuatedFixed-time

34

Mixed 2-phase

Normally the lowest time delay

35

Mixed phase with extra green

Good if the flow is unevenly distributed between the approaches

36

Separate left turn phase» Normally longer

average delay compared to mixed 2-phase

» Good from safety perspective

» Required at 70 km/h or 2 left turn lanes

37

Separate phases for each approach

» Normally inferior compared to mixed 2-phase, mixed phase with extra green and separate left turn phase

» Good from safety perspective

38

All pedestrian phase

39

Reduced pedestrian phase

40

Phase configuration

» The phase configuration shall be chosen as a compromise between the demands regarding

» Traffic safety and» Quality-of-service

for all kinds of road users!!!