Describing traveler choice behavior using the free utility model

Travel demand forecasting is an essential part of transportation planning and management. The four-step travel model is the traditional and most-common procedure utilized for travel demand forecasting, and many models have been proposed in the literature to describe each step separately. However, there is still a lack of a unified modeling framework that can successfully describe the collective choice behavior of travelers interacting with each other at different steps. This study uses the free utility model, whose objective function is mathematically consistent with the Helmholtz free energy in physics, to separately and simultaneously describe travelers' mode, destination, and route choice behaviors. The free utility model's basic assumption is that the travelers will trade off the expected utility and information-processing cost to maximize their own utility. This model provides not only a unified modeling framework for traveler choice behavior, but also provides a new perspective for understanding the user equilibrium model in transportation science and the potential game model in game theory.