Fuel economy ratings of cars and trucks will drop significantly starting with 2008 models, some of which will go on sale early next year.
According to a USA Today report, the declines are because the Environmental Protection Agency (EPA) is using more-realistic conditions to estimate the mileage cars and trucks will get. The vehicles themselves, in most cases, haven’t changed, only the formula used to assign fuel economy numbers.
Fuel-saving gasoline electric hybrids will see the biggest drops in the mileage numbers posted on their window stickers — as much as 30% worse in city driving, 20% worse on the highway, the EPA said after issuing new testing procedures.
Averaged over all vehicles of all types, city mileage ratings will drop 12% and highway numbers will fall 8%.
In what could be helpful to pickup and SUV shoppers, the new EPA rules require fuel economy numbers to be posted on medium-duty vehicles – those with a gross vehicle weight rating of 8.500 to 10,000 pounds — starting with 2011 models. Such vehicles, also known as three-quarter-ton and one-ton models, aren’t currently required to post mileage numbers.
Big changes to the 30-plus-year-old tests:
• Temperature: The new tests start with the car at 20 degrees Fahrenheit. The old tests started at 75 degrees. A cold vehicle uses more energy than a warm one. Cold temperatures are especially hard on the batteries that power hybrids, which is partly why those vehicles take such a big hit in the new ratings.
• Speed: The new tests use a maximum speed of 80 mph during the highway cycle instead of 60 mph in the old test, and 55 mph during the city portion instead of 56 mph. The city test always has been and continues to be closer to suburban driving conditions than true stop-and-go urban conditions.
The new test also includes hard acceleration. The old test used gentle acceleration.
That’s another reason hybrids suffer. Hard acceleration requires full use of the gasoline engine and little or no participation by the fuel-saving electric engine. “It’s not acting as a hybrid when you’re accelerating like that,” says Bill Wehrum, acting assistant administrator of EPA’s office of air and radiation, the office in charge of the testing that generates the fuel economy numbers.
• Air conditioning: The new test assumes it is used 13% of the time. The old test didn’t use air conditioning at all.
Air conditioning puts a drag on the engine and causes it to use more fuel. Wehrum says 13% is a high-enough figure because “some people don’t use it at all.”
Automakers will be allowed to include, through June, a line on the new window stickers saying what the mileage ratings would have been under the previous test.