Download - Measuring Impossible Behavior
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Measuring Impossible Behavior
How Do System Performance Metrics Need to Change When
Using Modeling Tools with Hard Capacity Limitations
Dan Tischler
14th TRB Planning Applications ConferenceMay 5th, 2013 • Columbus ,Ohio
Outline
• Background – SF and DTA• The capacity conundrum• DTA-appropriate metrics• Sharing time
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Modeling Framework
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ABM w/ StaticAssignment (CHAMP)
Analytical TrafficAssessment (Synchro)
Microsimulation(VISSIM)
Dynamic AssignmentModel (Dynameq)
Auto Demand in Subarea
IntersectionVolumes
Roadway Performance
Roadway PerformanceTransit Performance
AutoDemand
Transit &Non MotorizedDemand
LandUse
TransportationSystem
DTA Applications
• Freeway replacement• Bus rapid transit• Road closure• HOV ramps and lanes conversion• Congestion pricing (model dev. scenario
test)
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presidioparkway.org
bettermarketstreetsf.org/
http://www.sfcta.org
Reflections on Experiences
• The good• More realistic assignment (you can’t jam
unrealistic traffic through bottlenecks)• Backups that impact nearby links are
represented• Traffic patterns/paths change at
different times in response to varying traffic conditions
• Understands congestion for individual lanes and intersections
• Dynamic demand, even if we don’t fully use itSAN FRANCISCO COUNTY TRANSPORTATION
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Reflections on Experiences
• The so-so or not so good• Demand from ABM may not be
appropriate• Metrics used to interpret results provide
different answers• Travel demand modelers may lack traffic
operations experience
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Outline
• Background – SF and DTA• The capacity conundrum• DTA-appropriate metrics• Sharing time
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Hypothetical Project
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• Project to convert one freeway lane to HOV-only
• Will traffic diversions from the freeway affect transit?
Roa
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Arte
rial r
oadw
ay
Freeway
HOVProjectarea
Connector St
CBD
Static Model Results
• HOV lane pushes auto trips to the arterial
• Transit speeds and reliability worsen
• Indicates need for bus-only lane
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Roa
d-ba
sed
trans
it
HOVProjectarea
Diversions
CBD
Con
gest
ion
Dynamic Traffic Assignment Results
• More traffic stays on freeway
• Freeway speeds decline
• Some diversions go elsewhere
• Transit not impacted
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Roa
d-ba
sed
trans
it
HOVProjectarea
CBD
Congestion
DTA Hidden Story
• Bottleneck at signal causes long queues on Connector St
• Connector St has short green phase because volumes are currently low
• In practice traffic engineers would adjust signal capacity as travel changes
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Roa
d-ba
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trans
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HOVProjectarea
CBD
Queue
Bottleneck
Circular Feedback
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Capacity (signal timing)
Traffic volumes
Congestion
Policy decisions
What Are We Trying to Accomplish?
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?
LMFAO music videovia Youtube
Outline
• Background – SF and DTA• The capacity conundrum• DTA-appropriate metrics• Sharing time
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Do’s and Don’ts of Interpreting DTA Results
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Don’t only…
rely on V/C ratios or volumes alone as a
metric
assume that travel times tell the whole
story
Do consider…
queuing and its effects on the whole network
bottlenecks (assumptions or real
constraints)alternate routes
travel time and delay outside of the analysis
period
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Queuing
• Queues blocking intersections = poorly functioning network
• Possible measures• Tot length of all queues• Blocked intersections
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Vehicle Delay
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Waiting Vehicles
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Gridlock
Outline
• Background – SF and DTA• The capacity conundrum• DTA-appropriate metrics• Sharing time
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Sharing is Caring
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Thank you!
Dan Tischlerdan [dot] tischler [at] sfcta [dot] org