Investigating the Distribution of the Value of Time via Multiclass Traffic Assignment

Abstract

The unusual sensitivity of traffic assignment results over networks with tolled links to the assumed value of time (VOT), or, more specifically, the distribution of VOT across the population, is well known. This study proposes a methodology to generate a VOT distribution in a traveler population and to assign these travelers to a network by multiclass assignment so that the assigned-link volumes match a set of reference volumes. In the methodology, a discrete set of VOT is extracted from a VOT distribution. After groups of travelers from the origin–destination demand matrix are specified, a multiclass traffic assignment (MCTA) is performed to generate assigned volumes that fit the reference volumes. The proposed methodology is applied on a network example with the use of EMME/4 software to run the MCTA model. Of the available distributions, a gamma distribution is selected as the best-fitting distribution for the VOT. A sensitivity analysis around the mean and standard deviation of the gamma distribution also shows that the MCTA results are sensitive to the mean of the VOT distribution. In addition, for the example network, nine discrete values (i.e., traveler groups in the MCTA) from the VOT distribution are determined to be sufficient to capture the variation across the continuous VOT distribution.