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Coordinated Traffic Signal Timing

This document discusses coordinating signal timing between intersections to allow for efficient traffic progression. It defines key terms used in signal coordination like offset, bandwidth, and bandwidth efficiency. Example problems are provided to illustrate how to design signal coordination using space-time diagrams and calculate bandwidth efficiency. The goal is to time signals so that vehicles can travel through multiple intersections without stopping by ensuring green bands overlap between intersections. Good coordination is achieved with bandwidth efficiencies over 30%. Software tools can also be used to optimize coordination.

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AMAN FREDY
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464 views10 pages

Coordinated Traffic Signal Timing

This document discusses coordinating signal timing between intersections to allow for efficient traffic progression. It defines key terms used in signal coordination like offset, bandwidth, and bandwidth efficiency. Example problems are provided to illustrate how to design signal coordination using space-time diagrams and calculate bandwidth efficiency. The goal is to time signals so that vehicles can travel through multiple intersections without stopping by ensuring green bands overlap between intersections. Good coordination is achieved with bandwidth efficiencies over 30%. Software tools can also be used to optimize coordination.

Uploaded by

AMAN FREDY
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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COORDINATED SIGNAL TIMING

We have learned to calculate cycle length, splits, and clearance intervals for pretimed
traffic signals. This approach to design focuses on capacities of the various approaches
to an intersection. We will now change our focus to coordinating signal timing for
efficient traffic progression.
Coordination of traffic signals involves timing signals for opposing traffic streams with
relation to one another, so that vehicles traveling at predetermined speeds will be able to
successfully clear successive intersections on green.
In order to coordinate signals for opposing traffic streams, we use space-time diagrams.
Definitions:
Through band space-time path intersecting green at successive signals.
Band width width of total through band.
Offset- time difference between beginnings of green at two signals.

Offset

Time

Band width

Figure 1. Space-Time Diagram

B
Distance

We will be considering only simple situations, where signal coordination can be


determined by graphical methods, and calculations derived from the graph.
Example 1 Design and Evaluation
Given:
Two intersections spaced 1400 ft. apart
Design speed of progression = 40 ft/sec
60 second cycle with 50-50 splits
a. Find the offsets required for progression in the direction A to B.
b. Assuming AB is a two-way street, find the bandwidth in the opposite direction.
c. Calculate the bandwidth efficiency for each direction.

Time
(sec.)
120

90

65
60

35

Bandwidth
30

Offset of B
(relative to A)
5

1400
Space (ft.)

Figure 2. Analysis

Time
(sec.)
120

Reduction of Band (10 sec.)


95
90

Bandwidth
65

60

Bandwidth

30

35

1400
Space (ft.)

Figure 3. Evaluation
Steps:
Draw ideal band; Find loss; Find and draw total through band

BW
Quality assessment: Bandwidth efficiency =
100
C
Where: BW = width of total through band (sec)
C = cycle length (sec)

Time
(sec.)
120

90

65
60

35
30

1400
Space (ft.)

Figure 4. Final Product

Example 2 Evaluation of Existing Operation


Given:
Intersection spacing shown in Figure 5.
Design speed = 40 ft/sec
60 second cycle with 50-50 splits
Half cycle offset at intersection B
Quarter cycle offset at intersection C

1470 ft.

1330 ft.
A
Time
(sec.)

135

Figure 5. Block Spacing.

120

105

90

75
60

45

30

Offset B

15

Offset C

Figure 6. Show Ideal band, where edges hit red, calculate arrival times and signal
changes.

135

Time
(sec.)
120

105

90

75

3.25 sec. loss

60

45
BW = 21.75 sec.

5 sec. loss

30

Offset B

15

Offset C

A
Figure 7. Draw the Total Through Band.

135

Time
(sec.)
120

105

90

75
60

45
BW = 21.75 sec.

30

Offset B

15

Offset C

Figure 8. Find Ideal Band for Opposite Direction.

135

Time
(sec.)
120

BW = 5 sec.

105

90

75
60

45

BW = 21.75 sec.
30

Offset B

15

Offset C

A
Figure 9. Draw Total Through Band.

135

Time
(sec.)
120

105
90

BW = 5 sec.

75
60

45
BW = 21.75 sec.

30

Offset B

15

Offset C

A
Figure 10. Final Diagram.

Signal Coordination Summary


1. For this course, you must have a common cycle length for each intersection in
your system.
2. Identify the reference intersection, and determine all offsets with respect to it.
3. Offsets must be an increment between zero and the cycle length.
4. Progression band MUST go through entire system.
5. You must determine a bandwidth for each direction of traffic progression.
6. Good operation is achieved with bandwidth efficiencies of 30-40% or greater.
7. Cycle lengths and splits should be calculated so that all traffic is passed at each
intersection.
8. It is typically not possible to have full progression in both directions.
9. Available software:
a. Passer II
b. TRANSYT 7F (GA Optimization)
c. Synchro

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