Suburbanization and highways in Spain when the Romans and the Bourbons still shape its cities

We estimate the effects of highways on the suburbanization of Spanish cities. Based on Spain's historical roads - the almost 2000. years old Roman roads and the 1760 Bourbon roads -, we rely on an instrumental variables (IV) strategy because of the endogeneity of highway provision. Our results show that, first, each highway emanating from central cities caused an 8-9% decline in central city population between 1960 and 2011. Second, each highway ray fostered a 20% population growth in the suburbs, in particular in suburban municipalities where ramps were located. Finally, we confirm the increasing role of highways on shaping urban form: each additional kilometer closer to the nearest highway ramp increased municipal density growth by an 8%.