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."
The EPA has been reviewing its testing methodology and is asking car makers and other testing organizations to weigh in with their comments and suggestions. Millett says the agency has received a good deal of information and is confident it can propose changes and improvements to its lab procedures by next year.
Flawed Fuel Factors
But EPA critics, such as the Union of Concerned Scientists in Cambridge, Mass., say the disparities in fuel efficiency numbers for hybrids underscore a much larger problem: That the EPA's fuel efficiency tests are fundamentally flawed for all cars.
David Friedman, research director of the group's clean vehicles program, says the basic EPA testing parameters -- designed to capture emissions and pollution data -- are based on driving habits of decades past.
"The base test is 30 years old," said Friedman. "I wasn't driving back then, but it was a pretty different world."
According to Friedman's group, some of the more glaringly outdated driving assumptions and conditions that are still being used by the EPA in its efficiency tests include:
Low highway speeds. The EPA test assumes an average car speed of 48 mph and a maximum of 60 mph. Most state highway speed limits are now set at 65 mph or higher. At those speeds, fuel economy can drop by almost 10 percent to 17 percent, compared to 55 mph.
Easy acceleration. The maximum acceleration rate is 3.3 mph per second, or equivalent to taking about 18 seconds to go from 0 to 60 mph. By the EPA's own data, most drivers today accelerate nearly five times harder. The harder the acceleration, the more gas wasted.
Overestimated trip lengths. The EPA's "city" tests assume a trip of 7.5 miles. But even recent EPA figures show the average urban drive lasts five miles or even half that, at 2.5 miles. Shorter trips mean car engines do not have the time to warm up and operate efficiently.
Exclusion of air conditioning and other accessories. Rare luxury items 30 years ago, air conditioners are practically standard features on nearly every new vehicle in the United States. Heavy use of air conditioning and other accessories mean a severe reduction in fuel efficiency -- especially in stop-and-go traffic conditions.
"These testing cycles don't represent how people drive today," said Friedman. "They just aren't realistic."
And the unrealistic fuel efficiency numbers are generating a real cost for American consumers. By the Union of Concerned Scientists' estimates, U.S. drivers are spending $20 billion more on gasoline than they would expect based on the fuel economy stickers.
Fishing for Fixes
But Friedman and others are optimistic that the EPA is on the road to fixing the numbers issue. The agency's initial request for comments from other groups, including the Union of Concerned Scientists, is a promising sign, he says.
"The EPA is trying to address it and we're happy they're willing to address it," he said. "We're keeping the communication lines open with the EPA."
And so far, the EPA seems to be open or at least attentive to what others are saying needs to be fixed.
"In the 20 years since we updated the testing methodology, driving habits have changed. We have higher highway speeds, more congestion and greater use of accessories on new cars than before," acknowledged EPA's Millett. "All those factors will have to be added or considered."
Still, how -- or when -- those changes can be incorporated into the fuel efficiency tests is something the EPA has to figure out. And more importantly, Millett says any changes will have to be considered very carefully.
"It's also important to be consistent," he said. "We need to make sure that all makes and models are compared on an equal basis."