justification for this regression model was very limited. In particular, the regression model failed to account for changes over time in the fuels used to drive trucks and the changes in demand for diesel fuel from other uses.

As requested in TEA-21, BTS was asked not only to provide estimates of ton-miles and value-miles of international highway trade traffic, but also to investigate the reliability of these estimates. In response to this charge, the BTS report asserted that there are important improvements needed in many of the components of their estimation methods for reliably estimating ton-miles and value-miles. Generally speaking, the improvements are needed because of deficiencies, either in current data coverage and quality or with respect to access to data of higher quality that is collected but is currently unavailable.