SOURCE: U.S. Department of Transportation, Bureau of Transportation Statistics,
May 2002. Data for 2000 and 2001-U.S. Department of Commerce, U.S. Census
Bureau, Foreign Trade Division, U.S. Exports of Merchandise CD and U.S.
Imports of Merchandise CD, December 2000 and 2001. Data forother
years-based on U.S. Department of Commerce, U.S. Census Bureau, Statistical
Abstract of the United States (Washington, DC: annual years).