travel time variability after a shock: the case of the twin cities ramp metering shut off david...
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TRAVEL TIME VARIABILITY AFTER A SHOCK: THE CASE OF THE TWIN CITIES RAMP
METERING SHUT OFF
David Levinson, Lei Zhang
Department of Civil Engineering
University of Minnesota
Levinson, David and Lei Zhang (2001) Travel Time Variability After A Shock: The Case Of The Twin Cities Ramp Meter Shut Off, The Network Reliability of Transport (2003) Pergamon (editors Yasunori Iida and Michael Bell) (Presented at First International Symposium on Transportation Network Reliability, Kyoto, Japan July 30- August 1 2001).http://nexus.umn.edu/Papers/Variability.pdf
1. Introduction
Ramp Meter Shut Off
Experiment
Twin Cities
Oct. to Dec., 2000
Travel Time Variability
Studied Freeway
Locations
2. Measuring Travel Times
2.1 Overview
Trip Travel Time =
Freeway Mainline Travel Time, metering-off
Ramp Delay + Freeway Mainline Travel Time, metering-on
Freeway Segment 1 Freeway Segment 2 Freeway Segment 3
Ramp 1 Ramp 2 Ramp 3
OD Trip 1OD Trip 2
OD Trip 3
2.2 Methodology
Ramp Delay Calculation:
Queuing Diagram
Freeway Segments
q-k-v Relationship
Detector Field Length
OD Trips
Synchronize Ramp Delay
and Freeway Travel Time
to Find Trip Travel Time
Notations
t: index of time of day (5 minute intervals)
n: index of days
s: ramp status, off = without, on = with ramp meter control
: travel time
std(): compute standard deviation
ave(): compute average
V: inter-day travel time variation
v: intra-day travel time variation
D: difference of inter-day travel time variations (off - on)
v: average of intra-day travel time variation
3. Travel Time Variations
Inter-day Travel Time Variation
Intra-day Travel Time Variation
)...,,,( ,2,1,, ntttst stdV =
)...,,,( ,,2,1, ntnnsn stdv =
3. Travel Time Variations (cont’d)
Comparing Travel Time Variations: Metering-On vs. Metering Off
Inter-day:
For Each OD Pair, There is a
Vector of Dt for Different t’s. Range-Median Graph
Intra-day:
ontofftt VVD ,, −=
),...,,( ,,2,1 snsss vvvaveragev =
4. Results
4.1 Inter-day Travel Time Variation
Voff - Von > 0, statistically significant at level 0.01 for 103/124 OD Pairs: 26/45 for OD Pairs <= 3 miles, 77/82 for OD Pairs > 3 miles
Long Trips vs. Short Trips (<=3 miles)
Range-Median Graph for Each Freeway
4.2 Intra-day Travel Time Variation
voff > von
Long Trips vs. Short Trips
Inter-day Travel Time Variation: I494 Eastbound and Southbound
Inter-day Travel Time Variation: I494 Westbound and Northbound
Inter-day Travel Time Variation: TH169 Northbound
Inter-day Travel Time Variation: TH62 Westbound
Intra-day Travel Time Variation: I494 Eastbound and Southbound
Intra-day Travel Time Variation: I494 Westbound and Northbound
Intra-day Travel Time Variation: TH169 Northbound
Intra-day Travel Time Variation: TH62 Westbound
4. Results (cont’d)
4.3 Benefit Estimation for the Reduction on Inter-day Travel Time Variation (on average, 1.82 minutes per trip)
Small et al. (1999): $0.21 per minute of travel time standard deviation
Monetized benefits of improved travel time reliability:
$0.38 per trip
900,000 trips per PM peak in the Twin Cities 10 million dollars per year, savings during PM peak
only
4.4 A Simple Approach to Incorporate this Travel Time Reliability Improvement into Ramp Meter B/C Analysis
Apply a markup factor of 1.35 to value of time
5. Conclusion
Ramp Metering Improves Travel Time Reliability
Further Research on Monetizing the Value of Travel Time Reliability
Contact Information
David Levinson
Department of Civil Engineering, University of Minnesota
500 Pillsbury Drive SE, Minneapolis, MN 55455
E-mail: levin031@tc.umn.edu
Tel(O): 612-625-6354
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