This document describes a rigorous-engineering fuel-consumption test procedure that utilizes industry accepted data collection and statistical analysis methods to determine the change in fuel consumption for trucks and buses with GVWR of more than 10,000 pounds. The test procedure may be conducted on a test track or on a public road under controlled conditions and supported by extensive data collection and data analysis constraints. The on-road test procedure is offered as a lower cost alternative to on-track testing but the user is cautioned that on-road test may result in lower resolution (or precision) data due to a lack of control over the test environment. Test results that do not rigorously follow the method described herein are not intended for public use and dissemination and shall not be represented as a J1321-Type II test result.
The previous J1321 document lacked statistical analysis of test data and lacked constraints on test criteria required to resolve current and anticipated fuel consumption measurement increments. Additionally, results from previous versions of this procedure have been reported without precision tolerances. To address the current limitations of the procedure it was determined that a full revision of the document was required.