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Missouri University of Science and Technology and HDR Engineering

VARIABLE SPEED LIMIT DEPLOYMENT EVALUATION I-270/I-255 Traffic and Safety Conference May 12, 2010. Missouri University of Science and Technology and HDR Engineering. VARIABLE SPEED LIMIT. Task 1: Assessment of Law Enforcement and Public Opinions Task 2: VSL System Evaluation over Time

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Missouri University of Science and Technology and HDR Engineering

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  1. VARIABLE SPEED LIMIT DEPLOYMENT EVALUATIONI-270/I-255 Traffic and Safety Conference May 12, 2010 Missouri University of Science and Technology and HDR Engineering

  2. VARIABLE SPEED LIMIT • Task 1: Assessment of Law Enforcement and Public Opinions • Task 2: VSL System Evaluation over Time • Task 3: VSL System Evaluation over Space (Highway Segment)

  3. VARIABLE SPEED LIMIT • Task 1a Continuous On-line Public Survey • Task 1b Law Enforcement Paper Survey (2 times)

  4. VARIABLE SPEED LIMIT • Task 2.1 Average speed/lane by direction during peak and off-peaks • Task 2.2 Speed limit during peak period by direction • Task 2.3 Speed limit compliance by posted speed limit and direction

  5. VARIABLE SPEED LIMIT • Task 2.4 Travel times by direction • Travel Time in person-minutes • Travel Time Index = “Actual Travel Rate/Free Flow Travel Rate” • Task 2.5 Average traffic volumes during peak periods by direction • Task 2.6 Capacity, Evaluation of Delay, Queue Clearance and Occupancy

  6. VARIABLE SPEED LIMIT • Task 2. 7 Crash Rates • Crash Rates • Severity Rates • Affect of Speed Limit on Crash Rates • Task 2.8 Evaluation of Delay and Queue Clearance Times associated with crashes/incidents

  7. VARIABLE SPEED LIMIT • Task 3 – The VSL System has 22 Controlled Segments over the 38 mile corridor • Four segments will be evaluated with similar performance measurements identified in Task 2

  8. VARIABLE SPEED LIMIT OBJECTIVES: • Evaluation of performance measures • Pre and Post VSL system installation • Quantify the difference in fundamental traffic flow variables • Quantity Potential Benefits using Delay only • Cost savings in dollars

  9. VARIABLE SPEED LIMIT • Aggregation of 30 second data • Lane data used • Lane 2 adjacent to median and Lane 3 adjacent to shoulder • Lane 1 is the farthest left lane and lane 4/5 is the right/auxiliary lane • Purpose • Useful for data analysis • Travel Time: 5 min data used

  10. SEGMENT 3 SEGMENT 4 SEGMENT 1 SEGMENT 2 VARIABLE SPEED LIMIT

  11. VARIABLE SPEED LIMIT

  12. VARIABLE SPEED LIMIT • Daily Assessment • Thursday • Tuesday, Wednesday, and Thursday (monthly comparison) • Weather conditions • Clear • Rain • Snow • Interval: 15 min data used

  13. VARIABLE SPEED LIMIT

  14. VARIABLE SPEED LIMIT PRIMARY PERFORMANCE MEASURES 1) Speed 2) Volume - Capacity Estimation 3) Occupancy Analysis 4) Congestion Measures

  15. VARIABLE SPEED LIMIT Highway Capacity Manual (2000) definition for Roadway Capacity: “the maximum sustainable flow rate at which persons or vehicles reasonably can be expected to traverse a point or a uniform section of a roadway during a given time period, under prevailing conditions.”

  16. VARIABLE SPEED LIMIT CAPACITY ESTIMATION Functions based on Greenshield’s models Spline regression model (fitting the two different conditions congested and un-congested with two different straight lines and the point of intersection is the roadway capacity)

  17. VARIABLE SPEED LIMIT OCCUPANCY ANALYSIS Occupancy is the percentage of time when a short section of the highway is occupied Critical occupancy is the point where maximum flow occurs

  18. Critical Occupancy= 12.8% Critical Occupancy= 10.5% Pre: flatter slope Post: Steeper Slope CRITICAL OCCUPANCY

  19. VARIABLE SPEED LIMIT CONGESTION MEASURES • Measures of Effectiveness  • Travel Time • Total Delay • Percent of Congested Travel

  20. TRAVEL TIME Travel Time = Actual Travel Rate * Segment Length * Vehicle Volume * Vehicle Occupancy where: Travel Time is in person-minutes, Actual Travel Rate = 60/Average speed, in minutes per mile, Length of the segment is expressed in miles, Vehicle Volume is expressed in vehicles, and Vehicle Occupancy is expressed in persons/vehicles, 1.29. Travel time represents time of travel between detectors on the segment

  21. MODIFIED EQUATION: TRAVEL TIME L1 Station D1 Station D2 where: T1-2= travel time from station D1 to station D2, person-minutes, L1 = distance between station D1 and station D2, miles, V D1 , V D2 = average speed measured at station D1 and station D2, VOL D1 , VOL D2 = volume measured at station D1 and station D2

  22. TOTAL DELAY Total Delay = (Travel Time – PSL Travel Time) where: Total Delay is expressed in persons - minute, PSL stands for Posted Speed Limit PSL would have been 60 mph in the pre condition and displayed varied speed limit in the post condition.

  23. TOTAL DELAY Modified Total Delay: Total Delay = Post VSL Travel Time – Pre VSL Travel Time Total Delay is expressed in persons - minute PCT = Total Delay / Travel Time PCT = percent of congested travel

  24. VEHICLE MILES TRAVELED • VMT = Total Volume * Segment Length Average Volume Change Pre versus Post = between -0.2% and -1.0%

  25. VARIABLE SPEED LIMIT

  26. VARIABLE SPEED LIMIT

  27. VSL ACTIVATION LOGIC • Occupancy: >= 7 % • Volume: count > 10 vehicles/lane/30 seconds • Average speed: < 60 mph Activation Sequence • Posted variable speed limit signs start to flash Posted speed limit adjusted by 5 mph (40 to 60 mph) • Posted speed limit meters mainline traffic flows

  28. VARIABLE SPEED LIMIT • Analysis of 16 days of data • Total Segments: 4 • Total Detectors: 17 • Types of Analysis (for individual detectors): 5 • Types of Analysis (for a segment): 2 • Output: • 17 * 5 * 8 = 680 + 2 * 4 = 688 analysis/day • Data source approximately 1.4 billion lines of traffic data – average speed, volume, occupancy, per lane plus speed limit recommendation and current displayed

  29. VARIABLE SPEED LIMIT Final Report – End of 2010 • Acceptance Plan • Identification of Variables • Adaptive Algorithm • Explore European Concepts

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