According to the North American Freight Numbers released by the Bureau of Transportation Statistics (BTS) of the U.S. Department of Transportation, trucks transported 60.8 percent of U.S.-NAFTA trade in May 2013. Rail moved 15.1 percent of freight in May followed by vessels at 8.6 percent, pipelines at 6.8 percent and air at 3.9 percent. Combined surface trade transportation modes (truck, rail and pipelines) carried 82.7 percent of the total NAFTA freight flows.