Even Modest Increases in MPG Can Equal Big Gas Savings

Brian Handwerk
for National Geographic News
July 2, 2008

Sky-high gas prices this summer could have many drivers in the United States looking for a change, and most are well aware that buying a vehicle that gets better miles per gallon (mpg) will save them more dollars at the pump.

But not everyone looking for a switch wants to sacrifice passenger and cargo space by switching from a gas-guzzling SUV to a hyper-efficient compact.

What most Americans don't know is that even small boosts in efficiency can often save more fuel overall than much larger mpg gains in already-efficient vehicles, according to a new study.

In the paper, researchers at Duke University in North Carolina suggest that car buyers looking to upgrade their fuel efficiency need to think not in terms of mpg but in gallons per mile (a gallon is equal to about 3.8 liters).

Study co-author Richard P. Larrick said the idea was inspired by his own family's experience.

"We replaced a minivan with a station wagon. But it wasn't [immediately] obvious that if we replaced an 18-mpg vehicle with a 28-mpg [vehicle, that] it would be better than [upgrading the vehicle] from 33 to 50 mpg," he said.

"Once we did the math, we discovered it saved twice the gas, given our driving."

Making a Trade

For the new study, published last week in the journal Science, Larrick and Duke colleague Jack Soll polled consumers about fuel efficiency.

Many respondents didn't realize that a larger increase in the miles a car can drive on a gallon of gas does not always correlate to a greater increase in fuel savings, the authors found.

The researchers suggest that fuel-use comparisons between vehicles are far easier to understand when listed as total consumption per 10,000 miles (16,093 kilometers).

For example, an SUV that gets 10 mpg needs 1,000 gallons of gas to drive 10,000 miles. A 16-mpg station wagon, meanwhile, needs only 625 gallons to go the same distance.

Continued on Next Page >>


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