Meeting Higher Standards NYTimes.com

THERE’S more to the fuel-economy numbers on a vehicle’s window sticker than guidance for new-car shoppers, which explains why automakers work hard to get the best possible results on the federal tests.

Skip to next paragraph Related Cranking the Volt to 100 M.P.G. (November 16, 2008)

Under the authority of the Clean Air Act, the Environmental Protection Agency began requiring automakers to comply with tailpipe emission standards. The compliance test simulates rush-hour travel in Los Angeles; a car is driven on rollers while its exhaust is collected for analysis.

One spinoff from the emissions-certification process is the E.P.A.’s measure of fuel economy, which is a calculation based on the carbon content of the exhaust gas. City mileage test results were first published for new-car buyers in 1973, followed by highway mileage estimates in 1975.

The Energy Policy Conservation Act of 1975 directed the agency to require that automakers post mileage estimates on the window stickers of new cars and light-duty trucks. In an attempt to improve new-car mileage to 27.5 mpg by 1985, the first Corporate Average Fuel Economy, or CAFE, standard was established. An automaker’s CAFE number is a sales-weighted average of mileage for its light-vehicle fleet.

Manufacturers are penalized for each vehicle they sell that does not meet the standard. From 1983 to 2006, automakers have paid fines as high as million a year, for a total of 5 million over the 24-year period. DON SHERMAN