This SAE Recommended Practice was established to provide an accurate@ uniform and reproducible procedure for simulating use of heavy-duty hybrid-electric vehicles (HEVs) and conventional vehicles on dynamometers for the purpose of measuring emissions and fuel economy. Although the recommended practice can be applied using any driving cycle@ the practice recommends three cycles: the Manhattan cycle@ representing low-speed transit bus operation; the Orange County Transit Cycle@ representing intermediatespeed bus operation; and the Urban Dynamometer Driving Schedule (UDDS) cycle representing high-speed operation for buses and tractor-trailers. This document does not specify which emissions constituents to measure (e.g.@ HC@ CO@ NOx@ PM@ CO2)@ as that decision will depend on the objectives of the tester. While the recommended practice was developed specifically to address the issue of measuring fuel economy and emissions for hybrid-electric heavy-duty vehicles on a chassis dynamometer@ the document can also be applied to chassis testing of other heavy-duty vehicles. This document builds upon SAE J1711@ the light-duty HEV chassis recommended practice. As in SAE J1711@ this document defines a hybrid vehicle as having both a rechargeable energy storage system (RESS) capable of releasing and capturing energy and an energy-generating device that converts consumable fuels into propulsion energy. RESS specifically included in the recommended practice are batteries@ capacitors and flywheels@ although other RESS can be evaluated utilizing the guidelines provided in the document. Further@ the recommended practice provides a detailed description of state of charge (SOC) correction for chargesustaining HEVs. This document also has a section which provides recommendations for calculating fuel economy and emissions for charge-depleting hybrid-electric vehicles. It should be noted that most heavy-duty vehicles addressed in this document would be powered by engines that are certified separately for emissions. The engine certification procedure appears in the Code of Federal Regulations@ Title 40. NOTE- This document does not make specific provisions or recommendations for testing of bus and truck emissions with air conditioning deployed because the complexity of such tests is significant and is beyond the scope of the original document. It is recognized that a future practice that addresses air conditioning and other potentially large auxiliary loads is needed. Requirements Used to Develop the Recommended Practice- This document was developed to allow for the fair@ representative@ repeatable and accurate testing of heavy-duty vehicles so that direct comparisons can be made between hybrid-electric and conventional vehicles. To meet this goal@ the following guidelines have been followed: a. This document will provide a recommended practice to measure emissions and fuel economy of any type of conventional and HEV design including charge depleting and charge sustaining. b. Where applicable@ driver selectable modes may be evaluated (e.g.@ turning off regenerative braking and evaluating air conditioning influences). c. The use of the existing chassis test cycles provided with this document is highly recommended@ but this document allows for the creation or adjustment of test cycles to better represent the vehicle??s inuse application. d. Testing shall not require defeating or otherwise forcing a vehicle??s control system to perform differently from the way in which it would perform in use (potential exceptions include antilock brakes@ traction control and other systems that may affect dynamometer testing).