The Environmental Protection Agency plans to scrap the outdated testing procedures it uses to determine what kind of gas mileage automobile owners can expect, and to replace them with a new system that will factor in changes in automotive technology and how motorists actually drive.

According to the Washington Post, the changes were motivated by complaints from consumers who have been noticing that the mileage estimates in their owners manual often don't match the performance of their cars.

Consumers have become more concerned about the accuracy of mileage estimates as gas prices have soared in recent months. The complaints aren't really new, however. Consumer groups and even some automakers have been calling for changes to the rules for some time. The current procedures were established in 1977, and have not kept pace with changes in automotive technology and driving habits.

EPA Administrator Stephen L. Johnson said the new tests will take into account faster driving, more time spent idling in traffic, and more abrupt acceleration and braking.

"A lot has changed -- things such as speed limits, a lot more cars with air conditioning and other equipment," Johnson told the Washington Post. "Clearly, people do a little bit more stop-and-go and probably accelerate more than assumptions" accounted for in the original standards.

Johnson said a new system could go into effect in two years. Meanwhile, consumers will have to do what they have been doing all along:

• Take official mileage estimates with a grain of salt.
• Research the performance of individual vehicle models through resources such as Consumer Reports and Edmonds.com.
• Join online chat rooms devoted to people who own the type of car you're interested in buying.
• Talk to friends and mechanics who are familiar with the car of your dreams, to see whether your expectations match their experience.