International trade plays a substantial role in the economy of the United States. More than 1.6 billion tons of international merchandise was conveyed using the U.S. transportation system in 2001. The need to transport this merchandise raises concerns about the quality of the transportation system and its ability to support this component of freight movement. Measuring International Trade on U.S. Highways evaluates the accuracy and reliability of measuring the ton-miles and value-miles of international trade traffic carried by highway for each state. This report also assesses the accuracy and reliability of the use of diesel fuel data as a measure of international trade traffic by state and identifies needed improvements in long-term data collection programs.