This information report is a companion document to SAE Recommended Practice J1376, Fuel Economy Measurement Test (Engineering Type) for Trucks and Buses. It provides background information and explanations to better understand the measurement procedure and its use. It also provides references and data which were developed by the SAE/DOT Program in support of the particular limitations or parameters selected for the various items in the test procedure. The format used in this document is similar to the recommended practice so that corresponding topics can be found under the same headings.