aExport weights for land modes are estimated by the Bureau of Transportation Statistics using value-to-weight ratios derived from import data. bIncludes mail, other, unknown, and shipments through Foreign Trade Zones.
Notes: Percents do not add to 100 due to rounding. Excludes intransit data (merchandise shipped from one foreign country to another via a U.S. port). North American Free Trade Agreement (NAFTA) refers to U.S trade with Canada and Mexico.
Source: U.S. Department of Transportation, Research and Innovative Technology Administration, Bureau of Transporation Statistics, special tabulation and North American Transborder Freight Data, available at transborder.bts.gov as of October 2013.