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
Kimley-Horn
and Associates, Inc.

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. Wayne’s 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 that’s 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. With One-way ProgressionNB NB
With One-way Progression

7. With Two-way ProgressionSB 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. N Dallas Carrollton “Before” Cycle Lengths (PM Peak): PGBT Frankford
DNT
DNT
Marsh
Midway
Trinity Mills N
Carrollton
“Before” Cycle Lengths (PM Peak):
144 seconds seconds
80 seconds

19. N Dallas Carrollton “After” Cycle Lengths (PM Peak): PGBT Frankford
DNT
DNT
Marsh
Midway
Trinity Mills N
Carrollton
“After” Cycle Lengths (PM Peak):
160 seconds
80 seconds

20. N Dallas Carrollton “After” Cycle Lengths (PM Peak): 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 Client’s 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?

23. 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 safety’s 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”)

26. 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 model’s 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 model’s 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 system’s 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 client’s participation

33. Summary Good signal timing involves both art and science
Make wise use of the models… but don’t be afraid to use good judgment to improve the on-street result