Signal Coordination: Chapter 22

1
Lecture 11

• Signal Coordination Chapter 22

2
Objectives

• Factors affecting coordination
• Basic theory of signal coordination
• Application to arterial progression

3
Factors Affecting Coordination

• Benefits
• Purpose of signal system
• Factors lessening benefits
• Exceptions to the coordinated scheme

4
Concept Maximize Progression By Adjusting
Offsets
t3
Distance (ft)
t2
t1
0 30 60 90 120 150 180
210
Time (sec)
Note Definitions of offset vary, but text
convention is offset is t2 t1 and t3 t2
5
Benefits of Signal Coordination

• Stops and Delay
• Performance index combining measures
• Cost A X (total stops) B X (total delay)
• What are some other benefits?

6
Engineering Options

• What type of system is it?
• Which movements will be progressed?
• What is the objective?
• What happens if you can not achieve the objective?

7
Factors Lessening Benefits

• Inadequate roadway capacity
• Side friction
• Complicated intersection timing plans
• Wide variability in traffic speeds
• Short signal spacing
• Heavy turn volumes see figure 22-3

8
Time Space Diagrams and Ideal Offsets

• What is an offset?
• What is an ideal offset?

9
t3
Distance (ft)
t2
t1
0 30 60 90 120 150 180
210
Time (sec)
10
One-Way Progression

• For one-way progression, what do you need to know
  to estimate ideal offsets?
• How do you construct a time-space diagram?
• Can specify offsets relative to one (master)
  intersection

11
t3
Distance (ft)
t2
t1
0 30 60 90 120 150 180
210
Time (sec)
12
Effect of Queued Vehicles
How do you determine the offset with queuing?

• Q number of vehicles queued per lane (veh/lane)
• H discharge headway of queued vehicle (sec/veh)
• Loss1 loss time associated with vehicles starting
  from rest at the first downstream signal (sec)

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Different Types of Progression

• What are the different types of progression?
• Simple
• Forward
• Flexible
• Reverse
• Simultaneous

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Two-Way Progression

• Progression in one direction suffers
• Segment offsets tSBtNB nC
• Maximizing bandwidth
• Popular
• Limited

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Two-Way Progression (Cont.)

• Simultaneous progression
• Closely spaced intersections
• Queue management
• Alternate progression
• Uniform block length
• 5050 split
• N the number of blocks with simultaneous green
• How do you determine N?

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5th Signal
4th Signal
3rd Signal
Distance (ft)
2nd Signal
1st Signal
Working Line
0 30 60 90 120 150 180
210
Time (sec)
1000 ft intersection spacing 2 lanes in each
directions C 60 sec w/ 5050 split
What is the progression speed? What is the
nonstop volume?
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Two-Way Progression (cont.)

• What about arterials with non-uniform
  intersection spacing?

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Distance (ft)
Working Line
0 ½ C C 1½ C 2C 2½ C 3C 3½ C
Time (sec)
19
Distance (ft)
Working Line
0 ½ C C 1½ C 2C 2½ C 3C 3½ C
Time (sec)
20
A Signal Coordination Study

• Go to the field and ride through the system
• Do you see unused green time at down stream
  signals?
• Do you arrive at signals with standing queues?
• Do you arrive on red?
• Is the flow in the other direction significant?
• Sketch out network with flow patterns
• Which cycle length is most appropriate?

21
Oversaturated Conditions

• Removal of intersection blockage
• Address root causes
• Update signalization
• Use novel signalization to reduce extent of
  congestion
• Provide more space
• Prohibitions vs enforcement vs resulting problems
• Consider other options

22
Oversaturated Conditions

• Signal based remedies
• Metering plans
• Shorter cycle lengths
• Equity offsets
• Imbalanced split