externalities and their impact on regional innovation. We examine MSA-level patent data during the period 1975-2000 and find that … innovation output is higher in regions where large and small firms coexist. The finding is robust to across-region as well as …

We study the interplay between transportation infrastructure, knowledge flows, and innovation. Exploiting historical … variation, we estimate the effect of U.S. interstate highways on regional innovation. We find that a 10% increase in a region … flow of local knowledge and allow innovators to access more distant knowledge inputs. This finding suggests that …