Utility function for travel demand analysis under travel time uncertainty

Since the 1970s, it has been insisted by many researchers that the consideration of travel time uncertainty is very much influential for the estimation of traveler's behavior. However, none of these researchers has succeeded in explaining travelers' tendency of delayed risk avoidance with consistency in either theoretical or empirical aspect. Two reasons are considered: the first is the lack of consistent investigation of the accuracy of models proposed, and the second is the ambiguous definition of ‘uncertainty’ and ‘risk of delay’. Under these circumstances, the present paper discusses the inter-relationship of the models proposed in the past, and develops a new utility function to explain the travelers' behavior under travel time uncertainty. It is also demonstrated based on the practical data that the proposed utility function is well defined to estimate both the model choice and the route choice behavior of the traveler.