The advent of the U.S. Interstate Highway System provides an interesting experiment, which I use to identify the labor market effects of reduced trade barriers. This highway network was designed to connect cities and border crossings and to serve national defense, and as an unintended consequence it crossed many rural counties. I find that these counties experienced an increase in trade-related activities, such as trucking and retail sales. By increasing trade, the highways raised the relative demand for skilled manufacturing workers in skill-abundant counties and reduced it elsewhere, consistent with the predictions of the Heckscher-Ohlin model.
Guy Michaels (Fri,) studied this question.