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

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Presentation on theme: "VARIABLE SPEED LIMIT DEPLOYMENT EVALUATION I-270/I-255 Traffic and Safety Conference May 12, 2010 Missouri University of Science and Technology and HDR."— Presentation transcript:

1 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

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 VARIABLE SPEED LIMIT Segments 1I-64 to Route 100SB 2Route 21 to I-44NB 3Route 367 to I-170EB 4Route 370 to I-170WB SEGMENT 1 SEGMENT 2 SEGMENT 3 SEGMENT 4

11 VARIABLE SPEED LIMIT Time Periods Pre VSL Time PeriodsPost VSL Time Periods 1Start to mid Sept 07Start to mid Sept 08 2Mid to Last October 07Mid to Last October 08 3Start to mid Nov 07Start to mid Nov 08 4Start to mid April 08Start to mid April 09 5Dec 07 to mid Feb 08Dec 08 to mid Feb 09

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 Pre VSL System InstallationPost VSL System Installation 6 th September 20074 th September 2008 13 th September 200711 th September 2008 18 th October 200716 th October 2008 25 th October 200723 rd October 2008 8 th November 20076 th November 2008 15 th November 200713 th November 2008 10 th April 20089 th April 2009 17 th April 200816 th April 2009

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

15 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. VARIABLE SPEED LIMIT

16 CAPACITY ESTIMATION Functions based on Greenshields 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) VARIABLE SPEED LIMIT

17 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 Critical Occupancy= 12.8% Critical Occupancy= 10.5% Post: Steeper Slope Pre: flatter slope

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 L1L1 Station D 1 Station D 2 where: T 1-2 = travel time from station D 1 to station D 2, person-minutes, L 1 = distance between station D 1 and station D 2, miles, V D1, V D2 = average speed measured at station D 1 and station D 2, VOL D1, VOL D2 = volume measured at station D 1 and station D 2

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%



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 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 VARIABLE SPEED LIMIT

29 Final Report – End of 2010 Acceptance Plan Identification of Variables Adaptive Algorithm Explore European Concepts

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