摘要：Since changes in trade openness are typically confounded with other factors, it
has been difficult to identify the labor market consequences of increased
international trade. The advent of the United States Interstate Highway System
provides a unique policy experiment, which I use to identify the effect of
reducing trade barriers on the relative demand for skilled labor. The Interstate
Highway System was designed to connect major metropolitan areas, to serve
national defence and to connect the United States to Canada and Mexico. As a
consequence – though not an objective – many rural counties were also connected
to the highway system. I find that these counties experienced an increase in
trade-related activities, such as trucking and retail sales, by 7-10 percentage
points per capita. Most significantly, by increasing trade the highways raised
the relative demand for skilled manufacturing workers in counties with a high
endowment of human capital and reduced it elsewhere, consistent with the
predictions of the Heckscher-Ohlin model
