Federal Standards vs. On-the-road Usage
The Department of Transportation has set fuel economy -- or CAFE -- standards, measured in miles per gallon, for cars and light trucks since the 1978 model year. Manufacturers can go beyond these standards but are fined if their fleets fall behind the requirement.

The overall average fuel economy peaked in 1987 at 26.2 mpg, but declined over the next 14 years as fuel prices decreased and sport utility vehicle sales rose.

Actual road results, measured by the Environmental Protection Agency, have improved over the years, mostly due to foreign automobile manufacturers, which tend to produce higher mileage cars.

 More information on fuel standards