EPA alters test that determines fuel economy

That 55 mpg hybrid car you've been eyeing might end up being a 44 mpg car if you wait for the 2008 model.

The federal Environmental Protection Agency announced a new system Monday for evaluating fuel economy that will lower mileage estimates for most vehicles.

On average, vehicles rated under the 2008 method will post a 12 percent drop in city-driving mileage and an 8 percent decline in highway mileage, said Bill Wehrum, the EPA's acting assistant administrator for air and radiation.

The new requirements are an effort by the EPA to come up with mileage estimates that more closely reflect the real-world mileage people can expect when they purchase a vehicle.

Under the current system, which has been in effect since 1975 and was last changed in 1984, actual mileage is often far lower than the posted EPA mileage.

Hybrids will be hit harder because the new test eliminates some of the all-electric driving that helped them post impressive results under the present system, Wehrum said.

For the first time, the EPA also will require estimated mileage to be posted on medium-duty pickup trucks, vans and sport utility vehicles.

Such vehicles have been exempted from being rated because they were considered commercial trucks. But as growing numbers of Americans have adopted large SUVs and pickups as family vehicles, environmentalists and others have called on regulators to require mileage ratings for them as well.

A recent study by online automotive information provider Edmunds.com found the average real-world mileage for passenger cars and light trucks was about 14 percent less than EPA estimates.

In part, that's because the present EPA test doesn't include much stop-and-go traffic or lead-footed acceleration. Air conditioners aren't turned on, and all testing is done at 70 degrees Fahrenheit.

The new system will use more high-speed driving, part will be done in 20-degree cold, air conditioning will be used for some portion of each driving cycle, and there will be more stop-and-go and rapid-acceleration driving.

Mileage estimates for gas-electric hybrids probably will be 20 percent to 30 percent lower than they are now for city driving and 10 percent to 20 percent lower on the highway. That's because they quickly lose their all-electric advantage when operated in cold weather or when rapidly accelerated, Wehrum said.

"This is all about providing more and better information to consumers," he said

Toyota Motor Corp., which makes the popular Prius hybrid — now rated at 60 mpg in the city and 51 mpg on the highway (a combined rating of 55 miles a gallon) — supports the changes.

"This doesn't change the car or the technology, just the way the mileage is calculated," said Ming-Jou Chen, a company spokeswoman. "It makes the estimate closer to real-world numbers, and we fully support that."

Environmental groups applauded, too.

The EPA "did an excellent job" with the revisions, said Russell Long, executive director of the Bluewater Network, the San Francisco-based environmental group that sought the changes.

The new testing procedures can help motorists save money and reduce pollution by providing more accurate mileage information to use in car-buying decisions, Long said.