Hybrid Cars Reveal Mileage Rating Flaws

Dec. 10, 2004 — -- How many miles can your car travel on a single gallon of gas? If you think it's close to the fuel efficiency estimates provided by the Environmental Protection Agency, you'd probably be right. That is, unless you own one of those highly touted hybrid models.

According to EPA test ratings, gas-electric hybrid cars can travel 47 miles to 63 miles on a single gallon, depending on the vehicle model and options. But actual real-world performance, according to experts and owners, yields results that are far from the numbers produced in lab tests.

For example, the EPA rates the 2004 Toyota Prius at 55 mpg and the competing Civic Hybrid at 47.5 mpg for combined city and highway driving. But in May, Consumer Reports reported that in its independent road tests, the Prius got 44 mpg while the Honda hybrid netted 36 mpg.

Car makers, enthusiasts and experts are all quick to note that hardly any vehicle in the United States ever matches the EPA fuel efficiency rating listed. Most cars, industry watchers say, get about 10 percent to 15 percent less than their EPA rating. But among hybrid cars, the discrepancy may be as high as 30 percent, say some EPA critics.

EPA spokesman John Millett says the government agency realizes its fuel efficiency ratings may be flawed when compared to actual performance results. But Millett believes the EPA ratings still perform a valid and useful role for American car shoppers.

"The mileage numbers produced by our tests is for comparison among mix of models," said Millett. "If you choose the higher mileage [rating] of two different vehicles, you will always get the higher [mileage performance] of the two models regardless of what the actual rating [is]."

Still, Millett says the government agency has been aware of the growing concern about mileage rating disparities.

"If you're 10 percent off on a number for a pickup truck that gets 20 miles to the gallon, that's [just] 18 versus 20 miles per gallon," said Millett. But, "If you're 10 percent off 60 miles per gallon, that rating is now down to 54 miles per gallon, and that's very noticeable."