Current Practices in Traffic Signal Coordination

1
Current Practices in Traffic Signal
Coordination

• Presented by
• Wayne Kurfees
• Kimley-Horn and Associates, Inc.
• PE in AZ, IA, NC, TN, and TX
• Workshop on Best Practices for Signal Timing and
  Operations
• January 9, 2005

2
Disclaimer

• This presentation is based on current traffic
  signal coordination practices in the Dallas-Fort
  Worth Metroplex and may or may not reflect the
  state of the practice in other areas

3
Waynes Rules

• The motorists are the ultimate judges of the
  success of a signal timing project
• Before developing the new timing, be sure to
  understand the timing strategy thats currently
  in effect

4
General Philosophies

• Progression-based solutions
• Continuous green bands if possible, with
  appropriate consideration of the volumes turning
  onto and off of the arterial
• Otherwise, limit the number of stops for through
  traffic on the arterial

5
General Philosophies, cont.

• Optimize the phase sequence to achieve two-way
  progression

6
NB
NB
With One-way Progression
7
SB
SB
NB
NB
With Two-way Progression
8
General Philosophies, cont.

• When timing a grid of arterials, try to attain
  interlocking (i.e. both north-south and
  east-west) progression

9
Plano
Carrollton
Richardson
Addison
Garland
Farmers Branch
Dallas
10
General Philosophies, cont.

• Whenever possible, provide seamless progression
  across jurisdictional boundaries

11
Plano
Carrollton
Richardson
Addison
Garland
Farmers Branch
Dallas
12
Plano
Carrollton
Richardson
Addison
Garland
Farmers Branch
Dallas
13
Plano
Carrollton
Richardson
Addison
Garland
Farmers Branch
Dallas
14
Plano
Carrollton
Richardson
Addison
Garland
Farmers Branch
Dallas
15
Plano
Carrollton
Richardson
Addison
Garland
Farmers Branch
Dallas
16
Plano
Carrollton
Richardson
Addison
Garland
Farmers Branch
Dallas
17
General Philosophies, cont.

• Minimize the number of control groups

130
92
140
96
18
Dallas
PGBT
Frankford
DNT
DNT
Marsh
Midway
Trinity Mills
N
Carrollton

• Before Cycle Lengths (PM Peak)

144 seconds 160 seconds
80 seconds
19
Dallas
PGBT
Frankford
DNT
DNT
Marsh
Midway
Trinity Mills
N
Carrollton

• After Cycle Lengths (PM Peak)

160 seconds
80 seconds
20
Dallas
PGBT
Frankford
DNT
DNT
Marsh
Midway
Trinity Mills
N
Carrollton

• After Cycle Lengths (PM Peak)

160 seconds
80 seconds
21
Richardson
Garland
Dallas
22
Understand the Clients Preferences and
Limitations

• Minimum split times
• Coordinated phases
• Other through phases
• Left-turn phases
• Signal sequences
• Are lead-lag sequences allowed?
• Is it okay to use Dallas phasing (or similar
  techniques) to avoid the yellow trap if the
  leading side has protected-permissive left turns?
• Is it okay for the sequence to change as a
  function of the timing plan?

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Understand Any Special Requirements and
Limitations of the Particular Brand of System (or
Controller Type)

• Offset reference points
• Are splits in seconds or percent?
• Controller-specific limitations
• Example With at least one controller brand, you
  must add 1 second to the calculated minimum split
  times

24
Motorist Considerations

• Are the progression speeds realistic?
• What if the actual platoon speeds are greater
  than the posted speed limit?
• Whenever a major flow has to stop
• A short stop is better than a long one
• Try not to have the stop occur at an
  insignificant minor street
• For safetys sake, the platoon should arrive on
  red (rather than encounter an unexpected yellow)

25
Pedestrian Considerations

• Some locations require full accommodation of the
  pedestrian intervals
• CBD intersections (and other locations with
  significant pedestrian volumes)
• School crossings (at least during the crossing
  times)
• Coordinated phases
• Pretimed intersections
• Other locations without push buttons (if where
  pedestrian movements regularly occur)

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Pedestrian Considerations, cont.

• Otherwise, the minor-phase split will generally
  not accommodate the walk and ped clear intervals
  (and a resynchronization will have to occur after
  the ped call is served)

27
Use of the Optimization Model

• Understand the models strengths and weaknesses
• Make adjustments as needed to overcome the
  weaknesses
• Use the model as a tool but generally not as the
  final result

28
Timing Plan Development

• Build and calibrate the model
• Does it reflect what was observed on the street?
• Are progression speeds realistic?
• Use a master intersection
• Make the best use of the models optimization
• Make adjustments as appropriate

29
Timing Plan Development, cont.

• On-screen fine-tuning
• Eliminate excess time for minor phases
• Adjust non-critical phase times to provide the
  best re-start (i.e. try to avoid the need for
  multiple stops before getting back into the
  band
• Try to make more good things happen

30
Timing Plan Development, cont.

• Prior to beginning the implementation, review the
  proposed timing with the client on-screen

31
Timing Plan Implementation

• Prepare final timing in the appropriate format
• Make maximum practical use of automated
  interfaces between the optimization program and
  the signal systems database
• Double-check the database before the new timing
  plans actually operate on the street

32
On-street Fine-tuning

• Make the plans drive as smoothly as possible
  for the majority of the motorists
• Generally, make use of iterative, small
  adjustments
• Encourage the clients participation

33
Summary

• Good signal timing involves both art and science
• Make wise use of the models but dont be afraid
  to use good judgment to improve the on-street
  result