Roads and Innovation
利用历史规划的高速公路、铁路和探索路线数据，估计州际高速公路对区域创新的影响：高速公路存量增加10%导致五年内区域专利数量增加1.7%，机制是道路促进了本地知识流动。
We exploit historical data on planned highways, railroads, and exploration routes as sources of exogenous variation in order to estimate the effect of interstate highways on regional innovation: a 10% increase in a region's stock of highways causes a 1.7% increase in regional patenting over a five-year period. In terms of the mechanism, we report evidence that roads facilitate local knowledge flows, increasing the likelihood that innovators access knowledge inputs from local but more distant neighbors. Thus, transportation infrastructure may spur regional growth above and beyond the more commonly discussed agglomeration economies predicated on an inflow of new workers.