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.
This recommended practice provides a standardized test procedure to determine the change in a vehicle's fuel consumption by adding, removing, or modifying a vehicle component or system. The procedure utilizes two or more identical medium to heavy-duty single unit or combination vehicles weighing more than 10,000 pounds. Vehicles used in the test include an unchanging control vehicle, to provide reference fuel consumption, and test vehicle(s) that are modified during the test process. All vehicles are operated simultaneously and over the identical test circuit during each test run. The test procedure provides a percent difference in fuel consumption between two conditions of a test vehicle(s). A discussion of the data collection and statistical analysis approach are presented in Section 6 and Appendix B.