The Bureau of Transportation Statistics (BTS) gathers two datasets on freight ton-miles. Here, the data were compiled from a variety of modal sources to produce annual trend data. The original sources derive their data using various methods, as noted in the Data Source and Accuracy Statements in BTS’s National Transportation Statistics 2002. The other set of freight ton-miles data—discussed next—come from the Commodity Flow Survey conducted periodically by BTS and the U.S. Census Bureau of the Department of Commerce. Because the methodologies and coverage differ, the data may differ.