Increasing returns in transportation and the formation of hubs

The spatial structure of transport networks is subject to increasing returns in transportation, distance, and density economies. Transport costs between locations are thus, in general, endogenous, and are determined by the interaction between the spatial distribution of transport demand and these increasing returns, although such interdependence has long been ignored in regional models. By using a simple model, the present paper investigates the characteristics of viable hub structures (in terms of spacing and hierarchical relations) given the presence of density and distance economies in transportation.