Travel time savings are frequently one of the most important sources of benefit in transportation projects. Conventional methods of measuring value of travel time with revealed preference (RP) data or stated preference (SP) data have many drawbacks in application. In some aspects, however, RP data and SP data are mutually complementary and can be combined to give a convincing estimate of value of travel time. In this paper, the importance of measuring value of travel time based on activity-travel analysis rather than only on travel analysis is discussed. Then by applying economic theory the entire value of travel time (VOT) is indicated in two parts: the value of the decrease in disutility of travel (VOTT) and the value of the increase in utility induced by the use of travel time savings in activities (VOTA). The two parts are quite different in nature due to the fact that VOTT is mainly related to travel and VOTA is related to activity. By certain proper assumptions these two parts of VOT can be identified and analysed individually. Finally, an empirical procedure is suggested in which VOTT is first measured with SP data, then the entire VOT is measured by combining RP data and SP data. In application, such a procedure is able to provide an analytical comprehension of VOTT corresponding to travel and VOTA corresponding to activity.
Abstract