Spatial Productivity Spillovers from Public Infrastructure: Evidence from State Highways

Is public sector infrastructure a key determinant of productivity? Traditional, project-based analyses of benefits and costs typically do not find large rates of return. Proponents of infrastructure spending instead point to regression-based analyses of the links between private productivity and public infrastructure that imply large productivity effects from public spending. The disparity in estimated returns is often attributed to geographic spillovers in productivity benefits that are not captured by disaggregated analyses. We examine the degree to which state highways provide productivity benefits beyond the narrow confines of each state's borders. Despite the fact that state highways -- especially the interstate highway system -- are designed at least in part with interstate linkages in mind, we find no evidence of quantitatively important productivity spillovers.