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DTA Anyway Peer Review Panel

DTA Anyway Peer Review Panel. Traffic Flow Model Parameters Estimation. July 25 th , 2012. Problem Statement. Do … default traffic flow settings reflect local conditions? traffic flow parameter differences between facility and area classifications accurately reflect differences?

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DTA Anyway Peer Review Panel

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  1. DTA Anyway Peer Review Panel Traffic Flow Model Parameters Estimation SAN FRANCISCO COUNTY TRANSPORTATION AUTHORITY July 25th, 2012

  2. Problem Statement • Do … • default traffic flow settings reflect local conditions? • traffic flow parameter differences between facility and area classifications accurately reflect differences? • the slopes of San Francisco’s famously hilly streets affect traffic flow conditions (in a meaningful way)? Source: SF Citizen - http://sfcitizen.com/blog/tag/cable-cars/ SAN FRANCISCO COUNTY TRANSPORTATION AUTHORITY

  3. Dynameq Representation of Traffic Flow Flow (q) • Triangular fundamental diagram Saturation Flow Rate 1 1 FFS Critical Density (kc) Density (k) SAN FRANCISCO COUNTY TRANSPORTATION AUTHORITY

  4. Dynameq Representation of Traffic Flow • Parameters • Free-flow speed (FFS) - mph • Saturation flow rate (Qs) - pcuplph • Inverse of saturation flow headway (H) - sec • Response time (RT) - sec • Backwards wave speed (BWS) - mph • Jam density (Kj) - pcuplpm • Inverse of effective car length (EL) - ft SAN FRANCISCO COUNTY TRANSPORTATION AUTHORITY

  5. Relating “Real” Speed-Flow toDynameq Parameters • Challenges: • Triangular simplification forces compromises • Uninterrupted “flow-density”, “speed-flow”, or “speed-density” data is required (not available for all the network) • Use FFS, H, EL, and RT instead • Lack of data for RT and EL SAN FRANCISCO COUNTY TRANSPORTATION AUTHORITY

  6. Data Resources • Existing resources • Caltrans PeMS (for freeways) • SFMTA speed surveys • New resources • Traffic flow observations SAN FRANCISCO COUNTY TRANSPORTATION AUTHORITY

  7. Caltrans Performance Measurement System(PeMS) • Caltrans freeway sensors • Real-time and time-series traffic flow data • Counts, speeds, occupancy, etc. • San Francisco coverage: • 15 sensors • US-101, I-280, and I-80 • Resolution of 5-minute period, individual lanes • Reference period - May 2012. SAN FRANCISCO COUNTY TRANSPORTATION AUTHORITY

  8. Caltrans Performance Measurement System(PeMS) San Francisco sensor locations SAN FRANCISCO COUNTY TRANSPORTATION AUTHORITY

  9. Caltrans Performance Measurement System(PeMS) • Analysis • Generated hourly flow-density scatter plot • Piece-wise linear (triangular) curves were extracted from flow-density scatter plots for 59 freeway lanes in San Francisco • Non- triangular trends were excluded • 29 removed, 30 retained • Used for estimation of: • Free-flow speed • Backwards wave speed • Saturation flow rate SAN FRANCISCO COUNTY TRANSPORTATION AUTHORITY

  10. Caltrans Performance Measurement System(PeMS) Curve fitting for flow-density scatter plots Flow FFS BWS Kj=220 Density Fixed points SAN FRANCISCO COUNTY TRANSPORTATION AUTHORITY

  11. Caltrans Performance Measurement System(PeMS) Curve fitting – triangular plot example 1 Flow vs. density scatter points, Highway 280, Lane 3 at Mission St. SAN FRANCISCO COUNTY TRANSPORTATION AUTHORITY

  12. Caltrans Performance Measurement System(PeMS) Curve fitting – triangular plot example 2 Flow vs. density scatter points, Highway 280, Lane 3 at Alemany Blvd. SAN FRANCISCO COUNTY TRANSPORTATION AUTHORITY

  13. Caltrans Performance Measurement System(PeMS) Non-triangular density-flow plot example 1 Flow vs. density scatter points, Highway 280, Lane 4 at Vermont St. SAN FRANCISCO COUNTY TRANSPORTATION AUTHORITY

  14. Caltrans Performance Measurement System(PeMS) Non-triangular density-flow plots example 2 Flow vs. density scatter points, Highway 101, Lane 3 at 25th St. SAN FRANCISCO COUNTY TRANSPORTATION AUTHORITY

  15. San Francisco Municipal Transportation Agency (SFMTA) Speed Surveys • Speed data collected for speed limit determination • 500+ locations (~200 used for speed param. adjust) • Observation facility types • Arterial (most observations) • Local/Collector (limited observations) • Collection period from 2004 to 2012 • Methodology • 4 second headway requirement • Off-peak hours during normal weather conditions • 50th and 85th percentile speeds are used. SAN FRANCISCO COUNTY TRANSPORTATION AUTHORITY

  16. San Francisco Municipal Transportation Agency (SFMTA) Speed Surveys Area Type • AT=0 (reg’l core) 24 locs • AT=1 (CBD) 105 • AT=2 (urban biz) 164 • AT=3 (urban) 212 Facility Type • Super arterial 69 locs • Major arterial 187 • Minor arterial 134 • Collector 56 • Local 57 Slope • m < -8% 20 locs • -8% < m < 8% 467 • m > 8% 20 • Speed survey locations SAN FRANCISCO COUNTY TRANSPORTATION AUTHORITY

  17. San Francisco Municipal Transportation Agency (SFMTA) Speed Surveys 85th Percentile Speeds • 50th Percentile Speeds SAN FRANCISCO COUNTY TRANSPORTATION AUTHORITY

  18. DTA Project Traffic Flow Survey • Survey Design • Objective • Record saturation flow rate, backwards wave speed, and jam density on local, collector, and arterial streets of varying slope • Methodology • Observe jam density from queue spacing • Observe backwards wave and saturation flow during queue release SAN FRANCISCO COUNTY TRANSPORTATION AUTHORITY

  19. DTA Project Traffic Flow Survey Queue Dissipation Space Red Light H Saturation Flow EL Backward Shockwave RT Time SAN FRANCISCO COUNTY TRANSPORTATION AUTHORITY

  20. DTA Project Traffic Flow Survey • Collected data - vehicles • Vehicle type (car, truck, bus, motorcycle) • Queue positions • Front bumper distance from stop bar • Time when vehicle begins to move • Time when vehicle passes stop bar • Collected data - vehicles • Approximate slope of street • Lane width • Movement permission by lane SAN FRANCISCO COUNTY TRANSPORTATION AUTHORITY

  21. DTA Project Traffic Flow Survey • Ideal survey conditions • Single vehicle type – passenger cars • Consistently long queues (≥7 vehicles) • Smooth queue dissipation – no downstream backup • Absence of conflicts • Turning movement pedestrian conflicts • Lane changes SAN FRANCISCO COUNTY TRANSPORTATION AUTHORITY

  22. DTA Project Traffic Flow Survey • Challenges • Queue lengths • Low facility type (local /collector) streets lack adequate volume • Steep streets often lack heavy volumes • Need flaw in signal progression for queue formation • Congestion • Promising locations suffer from congestion • Conflicts • Need multiple lanes in order to observe through-movement-only lanes SAN FRANCISCO COUNTY TRANSPORTATION AUTHORITY

  23. DTA Project Traffic Flow Survey • Challenges (continued) • Vehicles do not cooperate ! • Tightening gaps after stopping What is the effective length? • Inching forward at start of green phase before car in front accelerates What is the response time? • Distracted drivers don’t notice the car in front is gone What is the headway? SAN FRANCISCO COUNTY TRANSPORTATION AUTHORITY

  24. DTA Project Traffic Flow Survey Survey Locations SAN FRANCISCO COUNTY TRANSPORTATION AUTHORITY

  25. DTA Project Traffic Flow Survey Collected Data Summary Statistics SAN FRANCISCO COUNTY TRANSPORTATION AUTHORITY

  26. Parameter Data Sources Data sources for parameters by facility type Red text = data limitations SAN FRANCISCO COUNTY TRANSPORTATION AUTHORITY

  27. Parameter Comparison • Comparison of original / default parameters to updated parameters (no slope variation) • Free-flow speeds increase in some ATs • Response time is slower • Jam density is lower • Saturation flow rates are lower by 100-300 pcuplph • Trade-off between saturation flow and response time • Matching either param. to data throws other off • Compromise is slightly high flow, slightly slow response SAN FRANCISCO COUNTY TRANSPORTATION AUTHORITY

  28. Parameter Comparison • Freeway SAN FRANCISCO COUNTY TRANSPORTATION AUTHORITY

  29. Parameter Comparison • Major Arterial SAN FRANCISCO COUNTY TRANSPORTATION AUTHORITY

  30. Parameter Comparison • Local Street SAN FRANCISCO COUNTY TRANSPORTATION AUTHORITY

  31. Parameter ComparisonIntroduction of Slope Variation • Slope-specific parameters not yet implemented in calibration model runs, but will be soon • Modify response time and saturation flow • Hold speed and effective length constant • Do not modify parameters on freeway FTs • Generally less steep • Slope data does not reflect skyway and underpass elevation SAN FRANCISCO COUNTY TRANSPORTATION AUTHORITY

  32. Parameter ComparisonIntroduction of Slope Variation Example: Major arterial in CBD area type Uniform parameters: FFS = 30 mph, EL = 24 ft SAN FRANCISCO COUNTY TRANSPORTATION AUTHORITY

  33. The End SAN FRANCISCO COUNTY TRANSPORTATION AUTHORITY

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