History
Fuel economy regulations were first introduced in 1978, only for passenger vehicles. The next year, a second category was defined for light trucks. These were distinguished from heavy duty vehicles by a gross vehicle weight rating (GVWR) of 6000 pounds or less. The GVWR threshold was raised to 8500 pounds in 1980 and has remained at that level through 2010. Thus certain large trucks and SUV's were exempt, such as the Hummer and the Ford Excursion. From 1979-1991, separate standards were established for two wheel drive (2WD) and four wheel drive (4WD) light trucks, but for most of this period, car makers were allowed to choose between these separate standards or a combined standard to be applied to the entire fleet of light trucks they sold that model year. In 1980 and 1981, respectively, a manufacturer whose light truck fleet was powered exclusively by basic engines which were not also used in passenger cars could meet standards of 14 mpg and 14.5 mpg. After 2010, new rules set varying targets based on truck size "footprint."
Read more about this topic: Corporate Average Fuel Economy
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