It's no secret that real-world gas mileage is often far different from what's listed on window stickers and in car commercials. That's because cars are tested for gas mileage in laboratories, under conditions that don't replicate the high speeds, hilly terrain, and heavy loads most drivers encounter.
To try to close the gap between the lab and the real world, the Environmental Protection Agency has mandated that automakers start using new tests that do account for real-world conditions like higher speeds, faster acceleration, air conditioner use, and cold weather.
The changes will be implemented beginning with the 2008 model year.
Integrated into the existing tests, the new procedures should result in significantly lower ratings.
We checked out the adjusted numbers for 10 cars, from hybrids to SUVs, and found that they decrease anywhere from 6 to 16 percent from their 2007 equivalents.
Hybrids and other gas-sippers will see the highest drops because their smaller, more-efficient engines typically have to work harder to achieve higher speeds, faster acceleration, and other new test criteria.
Despite the lower numbers, 2008 cars will be just as efficient as they were under the old ratings. The new ratings are simply an effort to close the gap between advertised figures and real-world mileage.
For the next few years, the EPA will allow automakers to use a standardized adjustment factor to calculate the new mileage figures for their vehicles instead of mandating that the cars be retested, EPA spokesman John Millett said. The same calculation will tell you what a pre-2008 model's mileage would be under the new tests.
This isn't the first time the EPA has adjusted its rating system; the last adjustment was in 1987.
Even with the changes, the 2008 guidelines won't be perfect. The new criteria don't account for everything - they assume flat terrain, no towing, and roughly 300 pounds of weight inside the car, including all occupants.
Driving with roof racks, using four-wheel drive, idling for long periods, and a number of other factors can reduce real-world gas mileage even further.
