Happy 2008! Your Prius’ Fuel Efficiency Just Dropped 16%

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Old-school Detroit must be smiling just a bit right now. After decades of providing unrealistic fuel-efficiency estimates—those big numbers touted in magazine ads and printed in large fonts on the vehicle-details stickers in new car lots—the U.S. Environmental Protection Agency has finally modified its method for calculating average miles per gallon, and the most fuel-efficient cars on the road have taken the biggest hit. Then again, they have a lot farther to fall.

The new method, which applies to all 2008 models and beyond, still doesn’t quite reflect actual driving conditions, but unlike the old numbers, which basically reflected your mileage in heaven (or, if you prefer, in an idealized lab setting), the new ones take into account things like acceleration, winter driving, air conditioner use, and realistic speeds (ever tried doing 55 in a 55 zone on a moderate-traffic day? It’s a recipe for abuse). Alas, the new formula appears to favor the gas guzzlers. Combined mileage for a 2007 Toyota Prius (automatic, 4 cylinder, 1.5 L engine) is down 16 percent under the new formula, to 46 mpg. The ’07 Honda Civic Hybrid is also down 16 percent, to 42 mpg.

On the other hand, the Hummer, that very symbol of anti-environmental profligacy, didn’t do as badly. The mileage for a 2007 H3 with 4WD only fell 12 percent. Its new EPA rating is 15 mpg.

Some of the very dirtiest dogs, the midlife-crisis vehicles, did almost as badly as the Prii, although to knock the mileage of a Ferrari 612 Scaglietti down 15 percent only required a drop of 2 mpg. It’s a fast car, but with its new EPA rating of 11 mpg (premium gas), it’ll drain wallets even faster. Ferrari’s 599 GTB (automatic, 12 cylinder, 5.9 liter engine) got luckier; it only lost 8 percent in its drop from 13 to 12 mpg—and who drives an automatic Ferrari, fer chrissake! Meanwhile, Lamborghini’s L-148 Mucielago (manual, 12 cylinders, 6.5 liters) dropped from 11 mpg to 10, a 9 percent loss. (You can find out how your own muscle car did here.)

The general trend was thus: The more beef under the hood, the less efficiency loss under the new calculation. The Ford Escape Hybrid and Toyota Accord Hybrid, which have bigger engines than the hybrid Civics and Prii, lost 13 percent EPA efficiency, leaving each with 27 mpg.

Now if only the agency could find a way to include guilt in its calculations…

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