Isolated Actuation, plus The Dilemma Zone Dilemma

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Isolated Actuation, plusThe Dilemma Zone Dilemma

• Rick Denney
• Iteris

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Actuated Controller Settings include

• Minimum Green (or Initial)
• Extension (or Passage)
• Volume-Density Variable Initial
• Volume-Density Variable Extension
• Maximum Green (or Maximum Extension)
• Coordination Settings

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Minimum Green Settings

• Clears queue from stop line to first detector
• Typical formula (variations do exist) is the sum
  of the startup time plus the time needed for each
  car in queue

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Volume Density Variable Initial

• Minimum initial
• Added initial (added per actuation)
• Maximum initial

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Variable InitialDiagram
Red
Green
Yellow
Each actuation increases initial
Maximum Initial
Controller Time Settings
Added Initial
Minimum Initial
Extension
Vehicles Detected
Vehicles Detected
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Variable Initial Settings

• Used in absence of stop-line detector
• Add to the minimum green for each car that passes
  over loop
• Typically added-per-actuation 2 sec.
• Minimum initial minimum green
• Maximum initial is 2 times the number of cars
  that will fit between stop line and loop

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Extension

• Maintains green when density is high
• Typically long enough for extending vehicle to
  clear dilemma zone
• With dilemma-zone detection, extension is part of
  the design
• With presence detection, extension long enough
  for expected gap

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Extension

• Extension X speed/(length of loop car),
  where X depends on your goals

X
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Extension

• Extension value a trade-off in heavy traffic

X?
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Volume Density Variable Extension

• Variable extension (gap reduction)
• Time before reduction
• Minimum gap
• Time to reduce, or reduce by

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Variable ExtensionDiagram
Green
Yellow
Time to Reduce, or Reduce By
Time Before Reduc-tion
Controller Time Settings
Extension
Minimum Gap
Initial Green
First Opposing Call
Gap Out
Vehicles Detected
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Variable ExtensionDiagram
Green
Yellow
Time to Reduce, or Reduce By
Time Before Reduc-tion
Controller Time Settings
Extension
Queue Clearance
Minimum Gap
Queue Gone
Initial Green
First Opposing Call
Gap Out
Vehicles Detected
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Variable Extension Settings

• Extension
• Generous for queue departure 2.5-3 sec.
• Time Before Reduction
• Long enough to clear typical queue
• Time to Reduce
• Typically 5-10 sec.
• Minimum Extension
• Short enough to only allow tight gaps 2 sec.

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Maximum GreenDiagram
Green
Yellow
Red
Maximum Green
Phase timer reaches Max, phase maxes out and
terminates
Controller Time Settings
Maximum Extension
Initial or Minimum Green
Extension
Vehicles Detected
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Maximum Green

• Doesnt care if you have dilemma zone protection
• Doesnt care if the queue is cleared
• Doesnt care if a platoon is arriving, but
• Often the only thing preventing insane cycle
  lengths

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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?

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Is There A Better Way?

• To improve safety without rewarding speeders?
• To keep cars from entering intersection
  dangerously?

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The Main Problem

• Dilemma zone protection set up at a point where
  cars should start to stop, but
• Its when they go that causes the problem
• DZ makes the decision to extend the green 6-9
  seconds before the problem
• Lots of detection infrastructure required, and
  sluggish timing unavoidable

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A Solution? (aka Research Needs)

• Delay the crossing green to prevent accidents,
  but
• Dont extend the green to reward the speeder
• Ergo A variable red clearance interval

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Variable Red Clearance Advantages

• Not concerned with stopping distancestopping
  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

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Disadvantages

• Controllers dont work that way
• Needs research to discover hidden disadvantages

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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