This report uses two datasets on freight ton-miles. For one source, the Bureau of Transportation Statistics (BTS) compiled the data from a variety of modal and other sources to produce annual trend data. The coverage of the modal data is often incomplete, and the BTS process of developing these data attempts to provide a more comprehensive estimate of all domestic freight ton-miles. For instance, while ton-miles data are readily available for the large Class I railroads, BTS estimates ton-miles for smaller railroads to arrive at total freight rail ton-miles.
The other set of freight ton-miles data come from the Commodity Flow Survey (CFS) conducted every five years by BTS and the U.S. Census Bureau of the Department of Commerce. As a survey, the methodology and coverage of this dataset differ from the above and the data are not comparable. For instance, according to the CFS, total 2002 ton-miles are 3.1 trillion and with supplemental estimates added rise to 4.5 trillion ton-miles.