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LIMITATIONS OF ADAPTIVE
SIGNALSDavid Hale (Leidos)
PREVIEW Ineffective heuristic methods Ineffective at certain congestion levels Lack of accountability Low market share Competing technologies
HEURISTIC METHODSASCT’s optimize complex networks in only a few seconds.Is this enough time to produce a good solution?Or, is it only enough time to produce a “quick and dirty” solution?Industrial engineering experts would not be impressed.
Fast Methods (not effective)“Equisat”Webster’s methodGreedy algorithmHill-climbing
Slow Methods (effective)Simulated annealingEvolutionary algorithmsDerivative-free methods
y z
x
Run Time
Dela
y R
ed
ucti
on
A
BC
ADAPTING VS. OPTIMIZING
(none)
Non-Adaptive,Quasi-Adaptive Fully Adaptive
Quick Optimization
Thorough Optimization
DEGREE OF SATURATION“If geared toward sporadic demand, they’re effective. In corridors with defined peaks and aggressive timing, they experience diminishing returns.”
Dela
y
Degree of Saturation
0.80
1.00
ACCOUNTABILITY“The industry needs a tool to quantify myriad adaptive products.”“People are implementing these systems without a real analysis.”
Proprietary, secret algorithms Capacity analysis? NO Simulation? DIFFICULT
Most products can’t do itVISSIM API = extra $$$Too much time, money, expertise
ACCOUNTABILITY“There is just way too much marketing.”
Advertising over science?Capitalism, good and badCherry-picked case studies67% said ASCT was good for oversaturated
conditionsLaw & Order
ITE Community discussion on ASCTExperts with decades of signal experienceASCT is just “one tool in the toolbox”ASCT “has its place”
MARKET SHARE“With less than 5% market share after 5 decades, acceptance is not consistent with successful technologies.”“Adaptive control in its infancy?”
Decades of availability (1960’s) SCATS (1976), SCOOT (1981) Fewer than 5% of signals are adaptive Why?
Costs too highUncertainty about benefits
COMPETING TECHNOLOGIES
“Automated performance measures allow agencies to optimize and manage signals without an adaptive system.”
Data driven Quasi-adaptive Stronger algorithms
RECENT QUOTES“The industry needs a tool to quantify myriad adaptive products.”
“People are implementing these systems without a real analysis.”
“If geared toward sporadic demand, they’re effective. In corridors with defined peaks and aggressive timing, they experience diminishing returns.”
“We only use them when other options have failed.”
“There is just way too much marketing.”
“Clearly the jury is out on where they should be deployed.”
“From my experience it is smoke and mirrors.”
“With less than 5% market share after 5 decades, acceptance is not consistent with successful technologies.”
“Automated performance measures allow agencies to optimize and manage signals without an adaptive system.”
MY CURRENT OPINION
Traffic too light = not cost effectiveDelay not sensitive below 80% saturation
Traffic too heavy = not cost effectiveEverything is pre-timed over 120% saturationNo platoon progressionCycle, offsets, phasing sequence insignificant
Traffic medium = sometimes cost effectiveSporadic demand (movie theater, football
stadium)Unpredictable pedestrian activityEmergency vehicles Incidents / accidents
LIMITATIONS OF ADAPTIVE
SIGNALSDavid Hale (Leidos)
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