Discontinuous changes in equilibrium retail activity and travel structures

The classical “Harris-Wilson” model of urban retail activity location is extended to include endogenous zonal retail prices, as well as endogenous travel costs. Illustrative equilibrium configurations of the activity/travel system are obtained through numerical experiments, under a variety of situations. Sudden changes in the spatial patterns of retail activity and interzonal shopping travel are shown to be induced by continuous variations in the values of the model's parameters. New sources of discontinuity are also identified, such as random fluctuations in the values of the exogenous variables, including residential population, link capacities and nonretail travel. Several directions for further theoretical and operational development of the model are discussed in conclusion.