Washington ? Car buyers will face a new form of sticker shock when they browse dealer lots next year: Mileage estimates will be down, reflecting the way people actually drive.

The Environmental Protection Agency on Monday issued new testing procedures that will cause fuel economy estimates on the stickers of new vehicles to drop an average of 12 percent for city driving on most 2008 model year vehicles, and 8 percent for highway driving.

The changes respond to consumer complaints that fuel economy is frequently less than advertised. EPA’s new system will take into account data from vehicle tests designed to more accurately assess high-speed driving, rapid acceleration, the use of air conditioning and driving in cold temperatures.

“EPA’s new fuel economy sticker ensures American motorists won’t be stuck with higher-than-anticipated charges at the pump,” said EPA Administrator Stephen L. Johnson in a statement.

The agency said no test can precisely predict the fuel economy of a vehicle because driving behaviors and conditions vary. But the test methods will help bring the estimates on the window stickers closer to the miles per gallon that drivers achieve on the road.

Stickers also will be upgraded to include fuel cost information, a graphic for comparing the fuel economy of different vehicles and a Web site address for more information.

Test results will not be used to determine whether automakers comply with laws requiring the U.S. fleet to have an average fuel economy of 27.5 miles per gallon for cars and 21 mpg for sport utility vehicles, pickup trucks and vans.

Those requirements are found in the Corporate Average Fuel Economy program, which is run by the Transportation Department and has separate regulations to determine fuel economy.