Tollroads are only part of the overall trip: the error of our ways in past willingness to pay studies
- 372 Downloads
With rare exception, actual tollroad traffic in many countries has failed to reproduce forecast traffic levels, regardless of whether the assessment is made after an initial year of operation or as long as 10 years after opening. Pundits have offered many reasons for this divergence, including optimism bias, strategic misrepresentation, the promise to equity investors of early returns on investment, errors in land use forecasts, and specific assumptions underlying the traffic assignment models used to develop traffic forecasts. One such assumption is the selection of a behaviourally meaningful value of travel time savings (VTTS) for use in a generalised cost or generalised time user benefit expression that is the main behavioural feature of the traffic assignment (route choice) model. Numerous empirical studies using stated choice experiments have designed choice sets of alternatives as if users choose a tolled route or a free route under the (implied) assumption that the tolled route is tolled for the entire trip. Reality is often very different, with a high incidence of use of a non-tolled road leading into and connecting out of a tolled link. In this paper we recognise this feature of route choice and redesign the stated choice experiment to account for it. Furthermore, this study is a follow up to a previous study undertaken before a new toll road was in place, and it benefits from real exposure to the new toll road. We find that the VTTS is noticeably reduced, and if the VTTS is a significant contributing influence on errors on traffic forecasts, then the lower estimates make sense behaviourally.
KeywordsValue of travel time savings Toll routes Free routes Choice experiment Errors in forecasts
We thank the three referees for their comments as well as Stephane Hess who have provided invaluable comments which have resulted in numerous improvements to the paper.
- Bain, R.: Toll Road Traffic and Revenue Forecasts. An Interpreters Guide. (2009b) ISBN 978-0-9561527-1-8Google Scholar
- Bain, R.: On the reasonableness of traffic forecasts, pp. 213–217. TEC Magazine, May (2011)Google Scholar
- Brownstone, D., Ghosh, A., Golob, T.F., Kazimi, C., Van Amelsfort, D.: Drivers’ willingness-to-pay to reduce travel time: evidence from the San Diego I-15 congestion pricing project. Transp. Res. Part A 37(4), 373–387 (2003)Google Scholar
- Flyvbjerg, B., Bruzelius, N., Rothengatter, W.: Megaprojects and risk: an anatomy of ambition. Cambridge University Press, Cambridge (2003)Google Scholar
- Hatton MacDonald, D., Morrison, M., Rose, J.M., Boyle, K.: Untangling differences in values from internet and mail stated preference studies, Fourth World Congress of Environmental and Resource Economists, Montreal Canada, June 28–July 2 (2010)Google Scholar
- Orne, M.T.: Demand characteristics and the concept of quasi-controls. In: Rosenthal, R., Rosnow, R.L., Kazdin, A.E. (eds.) Artifact in behavioral research, pp. 143–179. Academic Press, New York (1969)Google Scholar
- Orne, M.T.: The demand characteristics of an experimental design and their implications. Paper presented at the American Psychological Association, Cincinnati (1959)Google Scholar
- Smith, K., Shahidullah, M.: An evaluation of population projection errors for census tracts, Journal of the American Statistical Association, March 90 (429), Applications and Case Studies. Train, K. (2009) Discrete Choice Methods with Simulation 2nd Ed. Cambridge University Press, Cambridge (1995)Google Scholar