An equilibrium model of urban shopping activity allocation/travel distribution is developed, with endogenous travel costs and zonal prices of goods sold. At equilibrium, revenues in each zone balance the cost of operating zonal facilities supporting the activity. This cost is assumed to be a function of the level of activity (shopping trip ends), whereas zonal demands are a gravity-type function of the prives of goods and costs of travel. A simple "quasi-balancing" algorithm is used to illustrate the sensitivity of the equilibrium solution to values of the system's parameters. The resulting shopping activity/trip ends distributions are in conformance with standard location theory results. Also, when diseconomies of scale are present in activity supply, the equilibrium solution is always unique. Otherwise, discontinuities in trip ends and interzonal travel distributions may take place, depending on the magnitude of the zonal trip ends in the zones. Thus, the model is able to reproduce rich and complex spatial patterns of activity on the basis of the interaction of economic-type variables. In conclusion, further refinements are discussed.
Abstract