A Combined, Equilibrium Model of Urban Personal Travel and Goods Movements

A combined equilibrium model of urban personal travel and goods movements is developed, in which commodity flows are generated by the consumption of a commodity, as part of the conduct of a given, generic urban activity undertaken by individual consumers/travelers. A fundamental feature of the model is the explicit, full representation of the interacting behaviors of commodity consumers/travelers and commodity suppliers/shippers, within the framework of a spatial, competitive economy. Concurrently, passenger and freight flows take place on a common, congestible network, which is also used for general travel. Travelers/consumers are assumed to minimize their costs (activity plus travel) through their joint choice of an activity site and travel itinerary to it. Activity suppliers also minimize the costs of buying and shipping goods, through their joint choice of wholesaler and freight shipping routes. In both cases, activity costs are perceived randomly, and travel costs are perceived deterministically. Commodity supply meets demand at activity sites. Locational commodity prices are determined endogenously. The transportation network, in which a given link may or may not be shared by private cars and freight trucks, is in user equilibrium, for all users. As a special case, a spatial price equilibrium for the commodity is obtained. It is shown that, under certain conditions, the model always possesses a unique solution. An algorithm for obtaining that solution is described. In conclusion, several areas for further extensions of the model are discussed.