This part establishes fuel consumption standards pursuant to 49 U.S.C. 32902(k) for work trucks and commercial medium- and heavy-duty on-highway vehicles (hereafter referenced as heavy-duty vehicles), and engines manufactured for sale in the United States. This part establishes a credit program that manufacturers may use to comply with standards and requirements for manufacturers to provide reports to the National Highway Traffic Safety Administration regarding their efforts to reduce the fuel consumption of heavy-duty vehicles and engines.