Capital stock refers to the capital in existence on a certain date. To be classified as capital, an asset must be durable and expected to remain in service for at least one year. Assets expected to remain in service for less than a year are categorized as consumption goods. Capital stock for transportation infrastructure includes fixed structures such as railroad tracks, airports, transit stations, bus shelters, and locks and dams.

SOURCE: U.S. Department of Transportation, Bureau of Transportation Statistics, 2016.