Predicting Travel Time Variability for Cost-Benefit Analysis
VU University Amsterdam - Faculty of Economics and Business Administration
C. C. Koopmans
University of Amsterdam - SEO Economic Research
Erik T. Verhoef
VU University Amsterdam - Department of Spatial Economics; VU University Amsterdam - Faculty of Economics and Business Administration; Tinbergen Institute - Tinbergen Institute Amsterdam (TIA)
July 19, 2010
Tinbergen Institute Discussion Paper 10-071/3
Unreliable travel times cause substantial costs to travelers. Nevertheless, they are not taken into account in many cost-benefit-analyses (CBA), or only in very rough ways. This paper aims at providing simple rules on how variability can be predicted, based on travel time data from Dutch highways. The paper uses two different concepts of travel time variability. They differ in their assumptions on information availability to drivers. The first measure is based on the assumption that, for a given road link and given time of the day, the expected travel time is constant across all working days (rough information: RI). In the second case, expected travel times are assumed to reflect day-specific factors such as weather conditions or weekdays (fine information: FI). For both definitions of variability, we find that the mean travel time is a good predictor of variability. On average, longer delays are associated with higher variability. However, the derivative of travel time variability with respect to delays is decreasing in delays. It can be shown that this result relates to differences in the relative shares of observed traffic 'regimes' (free-flow, congested, hyper-congested) in the mean delay. For most CBAs, no information on the relative shares of the traffic regimes is available. A non-linear model based on mean travel times can be used as an approximation.
Number of Pages in PDF File: 26
Keywords: Travel time variability, Cost-benefit analysis, Mean-variance approach
JEL Classification: R40, R41, R42working papers series
Date posted: July 27, 2010
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