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News Notes
Science & Society
Real-world fuel economy test

On Feb. 1, the U.S. Environmental Protection Agency (EPA) rolled out a proposal to revamp its fuel economy tests, which tell consumers what mileage per gallon to expect from their new vehicles. In recent years, consumer groups and a number of car companies have joined environmental groups in calling for the overhaul, which is expected to take effect for model year 2008 cars.

Each year, EPA publishes a guide listing the fuel efficiencies of new cars, SUVs and light trucks. As mandated by federal law, labels on new car windows represent the gas mileage achieved in the EPA tests, which incorporate a weighted average of city to highway driving (55 percent to 45 percent, respectively), as measured in a constant-temperature lab (see Geotimes, November 2004).

The tests, however, are outdated and a poor measure of actual fuel use, says Lee Schipper, head of research at the World Resources Institute’s EMBARQ program in Washington, D.C., who published comparisons of fuel-economy standards for several countries in Transparent Policy in 1994. EPA’s tests were designed in the 1970s, and have not been modified since 1985, when EPA itself began adjusting its mileage 10 to 22 percent downward on the window stickers, to more accurately represent the mileage that consumers would get from their cars.

Bluewater Network, an environmental watchdog that petitioned EPA to revise its testing standards, says that EPA’s numbers are off by as much as 34 percent. Schipper says that the tests vastly underestimate the amount of time spent in city or congested driving, and they do not account for actual road conditions such as hills, curves and cold temperatures, or for the use of accessories such as air conditioning.

The tests also do not take into account changes in driver behavior, such as driving faster, Schipper says. No matter what, though, “the mileage will never exactly match what the stickers say because it is impossible to predict actual human behavior.”

In trying to “reflect changes in the way we drive,” three new tests will be run in addition to the standard highway and city driving simulation tests, says John Millet, a spokesman for EPA. The new tests are designed to capture factors that can significantly affect fuel economy: faster driving, more rapid acceleration, cold weather and the use of air conditioning, he says, as well as other car and road conditions.

EPA expects that fuel-economy estimates on new cars will likely be 10 to 20 percent lower due to the new tests, with estimates potentially 20 to 30 percent lower for hybrids. The agency will also modify its message on the actual stickers to better caveat the estimated mileage. “It is important for consumers to understand that their mileage will vary, depending on the driver, the road conditions and so on,” Millet says. “The single greatest variability is the foot of the driver on the accelerator.”

The revised tests and stickers are a step in the right direction, Schipper says, but “they will need to be checked again in a year or two.” Consumers need to realize, he adds, that EPA’s fuel-economy estimates are just that — estimates — and are designed to offer only a point of comparison between different cars. It remains to be seen, he says, whether the new tests change fuel-economy rankings between different cars, which might cause a stir in the auto industry.

The EPA-proposed tests are open for public comment until the end of this month.

Megan Sever

"Fuel economies, Part II," Geotimes, November 2004
U.S. Environmental Protection Agency Fuel Economy information

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