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