The purpose of this part is to specify one of the criteria in 49 U.S.C. chapter 329 “Automobile Fuel Economy” for identifying dual-fueled passenger automobiles that are manufactured in model years 1993 through 2019. The fuel economy of a qualifying vehicle is calculated in a special manner so as to encourage its production as a way of facilitating a manufacturer's compliance with the Corporate Average Fuel Economy standards set forth in part 531 of this chapter. The purpose is also to establish gallon equivalent measurements for gaseous fuels other than natural gas.