variable speed limit deployment evaluation i-270/i-255 traffic and safety conference may 12, 2010...
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VARIABLE SPEED LIMIT DEPLOYMENT EVALUATIONI-270/I-255
Traffic and Safety Conference May 12, 2010
Missouri University of Science and Technology
and HDR Engineering
VARIABLE SPEED LIMITTask 1: Assessment of Law Enforcement and Public Opinions
Task 2: VSL System Evaluation over Time
Task 3: VSL System Evaluation over Space (Highway Segment)
VARIABLE SPEED LIMITTask 1a Continuous On-line Public Survey
Task 1b Law Enforcement Paper Survey (2 times)
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
VARIABLE SPEED LIMITTask 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
VARIABLE SPEED LIMITTask 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
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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
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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
VARIABLE SPEED LIMITAggregation 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
VARIABLE SPEED LIMIT
Segments
1 I-64 to Route 100 SB
2 Route 21 to I-44 NB
3 Route 367 to I-170 EB
4 Route 370 to I-170 WB
SEGMENT 1
SEGMENT 2
SEGMENT 3 SEGMENT 4
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Time Periods Pre VSL Time Periods Post VSL Time Periods
1 Start to mid Sept 07 Start to mid Sept 08
2 Mid to Last October 07 Mid to Last October 08
3 Start to mid Nov 07 Start to mid Nov 08
4 Start to mid April 08 Start to mid April 09
5 Dec 07 to mid Feb 08 Dec 08 to mid Feb 09
VARIABLE SPEED LIMITDaily Assessment
◦Thursday◦Tuesday, Wednesday, and Thursday (monthly comparison)
Weather conditions◦Clear◦Rain ◦Snow
Interval: 15 min data used
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Pre VSL System Installation Post VSL System Installation
6th September 2007 4th September 2008
13th September 2007 11th September 2008
18th October 2007 16th October 2008
25th October 2007 23rd October 2008
8th November 2007 6th November 2008
15th November 2007 13th November 2008
10th April 2008 9th April 2009
17th April 2008 16th April 2009
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PRIMARY PERFORMANCE MEASURES 1) Speed2) Volume
- Capacity Estimation3) Occupancy Analysis4) Congestion Measures
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.”
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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)
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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
CRITICAL OCCUPANCY
0
200
400
600
800
1000
1200
1400
1600
1800
2000
0 7 14 21 28
Vol
um
e (V
ehs/
hr)
Occupancy (Percentage Time)
Pre VSL Uncongested Traffic Post VSL Uncongested TrafficPoly. (Pre VSL Uncongested Traffic) Poly. (Post VSL Uncongested Traffic)
Critical Occupancy= 12.8%
Critical Occupancy= 10.5%
Post: Steeper Slope
Pre: flatter slope
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CONGESTION MEASURESMeasures of Effectiveness
◦ Travel Time ◦ Total Delay ◦ Percent of Congested Travel
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
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
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.
TOTAL DELAYModified 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
VEHICLE MILES TRAVELEDVMT = Total Volume * Segment
Length
Average Volume Change Pre versus Post= between -0.2% and -1.0%
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VARIABLE SPEED LIMIT
VSL ACTIVATION LOGIC
Occupancy: >= 7 %Volume: count > 10 vehicles/lane/30
seconds Average speed: < 60 mph
Activation SequencePosted 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
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/dayData source approximately 1.4
billion lines of traffic data – average speed, volume, occupancy, per lane plus speed limit recommendation and current displayed
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VARIABLE SPEED LIMIT
Final Report – End of 2010
Acceptance Plan Identification of VariablesAdaptive AlgorithmExplore European Concepts