That means trading the SUV for the station wagon would save 375 gallons of gas.
By contrast, trading a 35-mpg sedan for a 50-mpg hybrid would save just 86 gallons of gas.
(Related: "Hybrid Cars Losing Efficiency, Adding Oomph" [August 2005].)
The researchers therefore recommend that Americans should focus on upgrading the worst gas guzzlers first.
"Which car should everyone be driving? They should be driving the 50-mpg car. But which one is more important to replace? It's that 10-mpg car," Larrick said.
"You don't have to replace [the gas-guzzler] with a 50-mpg car to save a lot of gas," he said. "You can replace it with a 20-mpg car and save a lot of gas."
U.S. Department of Energy researcher David Greene, who writes for Fueleconomy.gov, agrees that a change in how fuel efficiency is reported could help consumers make smarter choices.
"People working in this area have known for a long time that this is a problem and a cumbersome way to report fuel-economy numbers," said Greene, who works at Oak Ridge National Laboratory in Tennessee.
"In Canada and in Europe they use liters per a hundred kilometers, which obviously gives a better sense of the rate of fuel consumption," he said.
"Some auto companies, Honda for example, have been very much in favor of a change," he said. But so far U.S. officials seem reluctant to change a familiar system.
Therese Langer, a transportation expert with the nonprofit American Council for an Energy-Efficient Economy (ACEEE), advocates what she dubs a "crusher credit" to boost fuel efficiency among U.S. cars.
The controversial idea would pay drivers to scrap their low-mileage gas guzzlers.
"While we're trying to bring [new vehicle gas mileage] up as quickly as feasible in a cost-effective way, we also want to get some of these gas-guzzling vehicles off the road," she said.
Now is a good time, she said, because drivers of low mpg cars and trucks "may be suffering buyer's remorse with the gas prices they are paying."
But going after gas-guzzlers doesn't necessarily mean scrapping older vehicles.
"[Improvement in] fuel economy was basically flat from the late 1980s until last year," she said. "There's not really a good correlation between the age of the vehicle and how much [gas] it consumes."
Larrick, the study author, stressed that he doesn't want his research to be misconstrued as an invitation to drive anything other than the most fuel-efficient car compatible with a person's needs.
"We're not advocating for people to buy low mpg vehicles," he said. "We are advocating for people to replace the most inefficient cars with more efficient ones."
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