Using a range of nonparametric methods, the paper examines the specification of a model to evaluate the willingness-to-pay (WTP) for travel time changes from binomial choice data from a simple time-cost trading experiment. The analysis favours a model with random WTP as the only source of randomness over a model with fixed WTP which is linear in time and cost and has an additive random error term. Results further indicate that the distribution of log WTP can be described as a sum of a linear index fixing the location of the log WTP distribution and an independent random variable representing unobserved heterogeneity. This formulation is useful for parametric modelling. The index indicates that the WTP varies systematically with income and other individual characteristics. The WTP varies also with the time difference presented in the experiment which is in contradiction of standard utility theory.

Using nonparametrics to specify a model to measure the value of travel time

This paper presents the findings of a study looking into the valuation of travel time savings (VTTS) in Switzerland, across modes as well as across purpose groups. The study makes several departures from the usual practice in VTTS studies, with the main one being a direct representation of the income and distance elasticity of the VTTS measures. Here, important gains in model performance and significantly different results are obtained through this approach. Additionally, the analysis shows that the estimation of robust coefficients for congested car travel time is hampered by the low share of congested time in the overall travel time, and the use of an additional rate-of-congestion coefficient, in addition to a generic car travel time coefficient, is preferable. Finally, the analysis demonstrates that the population mean of the indicators calculated is quite different from the sample means and presents methods to calculate those, along with the associated variances. These variances are of great interest as they allow the generation of confidence intervals, which can be extremely useful in cost-benefit analyses.

Income and Distance Elasticities of Values of Travel Time Savings: New Swiss Results

On the Theory of the Valuation and Allocation of Time: Reply

Enhancing the economic benefit assessment of roadway investment through the application of value of time by trip length

Congestion pricing has been regarded as an effective method of reducing networkwide travel cost. Previous work on the toll-design problem focused on the deterministic network, assuming that the network operates deterministically without uncertainty. This essentially precludes investigating the recently proposed travel time reliability indices as a system performance measure to evaluate and prioritize the selection of future investment strategies. In this study, the authors investigate various recently proposed travel time reliability measures in determining the optimal toll strategies to improve travel time reliability in the network. A simulation-based genetic algorithm (SGA) procedure is developed to solve the stochastic bi-level programming problem. The experimental results using a simple test network show that optimal toll determined by the misery index can improve both travel time reliability for network users and total travel time for the network planner.

Investigating Travel Time Reliability Measures in Toll Design Problem

In order to investigate the issues in measurement of value of travel time savings (VTTS), the willingness-to-accept (WTA) for the private car owner is studied by using surveyed data. It is convincing that trip purpose, trip length, time savings, cost savings, income, and allowance from employee have effects on the WTA. Moreover, influences of these variables are not the same for different trip purposes. For commuting trips, effects of income and allowance from employee are significant while time savings and cost savings are dominated for leisure and shopping trips. It is also found that WTA is much higher than expected which implies that there are a group of drivers who are not prone to switching to other trip modes other than passenger car.

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Xiao-ming Liu

Papers

Valuation of travel time savings in viewpoint of WTA