New vehicle fuel economy stickers will show most 2008 models getting 10 percent to 20 percent less mileage in city driving and 5 percent to 15 percent less in highway use.

Gasoline-electric hybrids will be affected even more, with ratings for city driving decreasing an average of 20 percent to 30 percent. From an over estimated 57 mpg to reality of 33 mpg .The long-awaited proposal is the first attempt in 20 years to alter the formula used by the EPA to estimate new vehicle fuel economy. That formula determines what fuel economy estimates appear on the stickers of every new car in showrooms .

“Since the time of the last revisions to EPA's methods for measuring fuel economy (1985), many conditions have changed — speed limits are higher, congestion has increased, and more vehicles are equipped with power-hungry accessories, like air conditioning,” the EPA said in a statement ahead of the announcement. “All of these factors will impact a vehicle's actual fuel economy.” Estimates are based on outdated driving patterns.

Currently, the EPA relies on data from two lab tests for the city and highway estimates. They’re done in mild conditions, when the temperature is 75 degrees, using top highway speeds of 60 mph and average speeds of 48 mph. Those conditions, the EPA acknowledges, are “generally lower than those experienced by drivers in the real world.”