trb signal timing best practices workshop 2005 isolated actuation, plus the dilemma zone dilemma...
TRANSCRIPT
TRB Signal Timing Best Practices Workshop 2005
Isolated Actuation, plusThe Dilemma Zone Dilemma
Rick Denney
Iteris
TRB Signal Timing Best Practices Workshop 2005
Actuated Controller Settings include
Minimum Green (or Initial)Extension (or Passage)Volume-Density: Variable InitialVolume-Density: Variable ExtensionMaximum Green (or Maximum Extension)Coordination Settings
TRB Signal Timing Best Practices Workshop 2005
Minimum Green Settings
Clears queue from stop line to first detectorTypical formula (variations do exist) is the sum
of the startup time plus the time needed for each car in queue:
length vehicledetectorfirst to distance
s/veh 2 s 5 Green Minimum
TRB Signal Timing Best Practices Workshop 2005
Volume Density: Variable Initial
Minimum initialAdded initial (added per actuation)Maximum initial
TRB Signal Timing Best Practices Workshop 2005
Variable Initial—Diagram
Vehicles Detected
Minimum Initial
Extension
Vehicles Detected
Each actuation increases initial Maximum Initial
Con
trol
ler
Tim
e S
etti
ngs
Added Initial
Red Green Yellow
TRB Signal Timing Best Practices Workshop 2005
Variable Initial Settings
Used in absence of stop-line detectorAdd to the minimum green for each car
that passes over loopTypically “added-per-actuation” = ~ 2 sec.Minimum initial = minimum greenMaximum initial is 2 times the number of
cars that will fit between stop line and loop
TRB Signal Timing Best Practices Workshop 2005
Extension
Maintains green when density is highTypically long enough for extending
vehicle to clear dilemma zoneWith dilemma-zone detection, extension is
part of the designWith presence detection, extension long
enough for expected gap:
TRB Signal Timing Best Practices Workshop 2005
Extension
Extension = X – speed/(length of loop + car), where X depends on your goals…
0 2 4 6 8 10 12
P(ga
p) PDF of queue departure gaps
PDF of arrival gaps
Gap
Low Flow Conditions
X
TRB Signal Timing Best Practices Workshop 2005
Extension
Extension value a trade-off in heavy traffic…
0 2 4 6 8 10 12
P(ga
p) PDF of queue departure gaps
PDF of arrival gaps
Gap
High Flow Conditions
X?
TRB Signal Timing Best Practices Workshop 2005
Volume Density: Variable Extension
Variable extension (gap reduction)Time before reductionMinimum gapTime to reduce, or reduce by
TRB Signal Timing Best Practices Workshop 2005
Variable Extension—Diagram
Minimum Gap
Initial Green
Vehicles Detected
Extension
Time to Reduce, or
Reduce By
Time Before Reduc-tion
Con
trol
ler
Tim
e S
etti
ngs
First Opposing Call Gap Out
Green Yellow
TRB Signal Timing Best Practices Workshop 2005
Variable Extension—Diagram
Minimum Gap
Initial Green
Vehicles Detected
Extension
Time to Reduce, or
Reduce By
Time Before Reduc-tion
Con
trol
ler
Tim
e S
etti
ngs
First Opposing Call Gap Out
Green Yellow
Queue ClearanceQueue Gone
TRB Signal Timing Best Practices Workshop 2005
Variable Extension Settings
ExtensionGenerous for queue departure: ~2.5-3 sec.
Time Before ReductionLong enough to clear typical queue
Time to ReduceTypically 5-10 sec.
Minimum ExtensionShort enough to only allow tight gaps: ~2 sec.
TRB Signal Timing Best Practices Workshop 2005
Maximum Green—Diagram
Vehicles Detected
Maximum Green
Maximum Extension
Initial or Minimum Green Extension
Phase timer reaches Max, phase maxes out and terminates
Con
trol
ler
Tim
e S
etti
ngs Green Yellow Red
TRB Signal Timing Best Practices Workshop 2005
Maximum Green
Doesn’t care if you have dilemma zone protection
Doesn’t care if the queue is clearedDoesn’t care if a platoon is arriving, butOften the only thing preventing insane
cycle lengths
TRB Signal Timing Best Practices Workshop 2005
Some Biased Questions
Does the dilemma zone really exist?What is the real purpose of dilemma zone
protection?Prevent accidents from cars going too fast, too
close?Reward fast drivers with longer green?
TRB Signal Timing Best Practices Workshop 2005
Is There A Better Way?
To improve safety without rewarding speeders?
To keep cars from entering intersection dangerously?
TRB Signal Timing Best Practices Workshop 2005
The Main Problem
Dilemma zone protection set up at a point where cars should start to stop, but
It’s when they go that causes the problemDZ makes the decision to extend the
green 6-9 seconds before the problemLots of detection infrastructure required,
and sluggish timing unavoidable
TRB Signal Timing Best Practices Workshop 2005
A Solution? (aka Research Needs)
Delay the crossing green to prevent accidents, but
Don’t extend the green to reward the speeder
Ergo: A variable red clearance interval
TRB Signal Timing Best Practices Workshop 2005
Variable Red Clearance: Advantages
Not concerned with stopping distance—stopping cars are already stopping
Concerned with cars that are still going at the end of the yellow
Measured close to the stop line, where detection is cheap and easy
Detects problems where they exist instead of projecting them 6-9 seconds back
TRB Signal Timing Best Practices Workshop 2005
Disadvantages
Controllers don’t work that wayNeeds research to discover hidden
disadvantages
TRB Signal Timing Best Practices Workshop 2005
Summary (Yup, this is biased, too)
Old methods used fancy timing to work with limited detection
New methods use fancy detection layouts that add more and more green time to serve less and less traffic
None solve the problem: Clearance problems should affect clearance intervals, not green time