The accessibility city : when transport infrastructure matters in urban spatial structure

At the present time, most large cities in the world are polycentric and, at the same time, they are undergoing a process of employment and population decentralization. Gordon and Richardson (1996) argued that polycentricity is just an intermediate stage between monocentricity and a more unstructured, chaotic and amorphous location model, the dispersed city. Focusing their attention only on main centers, they neglected the role of transport infrastructure on urban spatial structure. On the contrary, New Urban Economics theoretical models (e.g. White, 1976; Steen, 1986; Sullivan, 1986) show that employment and population location is structured not only around main centers, but also around transport infrastructure. In a context of employment and population decentralization, transport infrastructure might be reinforcing its location role and a new location model might emerge, the accessibility city, in which employment and population continue to be concentrated but close to transport infrastructure and with more low-density settlements. For the case of the Barcelona Metropolitan Region, we study the spatial distribution of population and its evolution between 1991 and 2006. The goal is to provide some insight into the location model discussion by taking into account the role of transport infrastructure and, therefore, considering the accessibility model as an alternative spatial configuration. Results reveal a multi-nodal distribution for population, with movements that are, indeed, away from the main centers but often into transport infrastructure. As a result, the accessibility city seems to be emerging.