For decades new car buyers have complained that their fuel economy has not measured up to the EPA estimates on the window sticker. Since the EPA began providing mileage estimates in the 1970’s, it has been known that the testing methods were not reflective of real world driving conditions and are more effective in comparing mileage between different models than determining actual fuel economy.

Although changes have been made to this fuel economy estimating system several times since the 70’s, new tests and formula for determining mileage and, as well as new window stickers, will be phased in with the 2008 model year, and new testing procedures will be mandatory by 2011.

It is speculated that the estimated mileage appearing on window stickers will be reduced in most models, but that these figures will more closely match the real world mileage of the vehicle. For drivers practicing good driving habits and maintenance, they may be able to get fuel economy that is higher than estimated.

Current fuel mileage tests are done with vehicles on a treadmill-like device designed to simulate real driving. However, these tests are done in moderate temperatures without any accessories running, such as air conditioning. The highway test is far outdated, with the top speed only being 60 mph, and an average speed of 48 mph. The city driving test simulates 7.5 miles of driving at an average of 20 mph with 18 stops.

The new fuel economy testing procedures will take into account and replicate three common scenarios that can significantly lower fuel economy, such as hard acceleration, cold temperature operation, and the use of air conditioning. Although some of these tests are done currently, they are used to determine emissions figures, but the data is factored into mileage estimates. For the 2008 model year, the EPA is simply using a different formula in an attempt to make mileage estimates more accurate.

It is expected that the new estimation formula and new testing procedures will lower fuel economy ratings by 10-30% across the board. The vehicles whose mileage ratings will see the biggest reduction are likely to be ones that are adversely affected by heavy demand on the engine from hard acceleration, air conditioning, and cold temperatures, such as high mileage cars.

Many environmentalists are disappointed that hybrids are expected to be among the vehicles with the biggest drop in estimated mileage. Some say this may have a negative impact on the hybrid market, but every vehicle will have the same actual fuel economy. The only difference is a more realistic mileage estimate.

While some fear this will cause consumers to neglect hybrid cars, many analysts and industry insiders see the new formula and tests in a positive light. Dave Alexander, a senior analyst at ABI Research, said, “There is potential in the long run for better customer satisfaction.” This is because a car whose window sticker says 30 mpg will be able to produce that mileage at 70 mph with the air conditioning on, in real driving conditions, instead of at a top speed of 60 mph with no accessories in a climate controlled setting.

Instead of turning consumers away from hybrids, more accurate mileage estimates may allow consumers to purchase vehicles that are actually more fuel efficient instead of continuing to be dissatisfied with lower than expected mileage.