Gallons Per Mile: Does It Make More Sense?

June 19, 2008
We're used to thinking of fuel economy in miles per gallon, but would it make more sense to think about "gallons per mile?"

That's the tenet of a new study from Science magazine and Duke University's Fuqua School of Business. The study, due in the June 20 issue of the magazine, takes the stand that gallons per mile will "help consumers make better decisions about car purchases and environmental impact."

To assemble the study and their conclusions, Duke professors Richard Larrick and Jack Soll experimented with drivers' reactions to fuel economy and, according to the magazine, found that people generally think fuel use drops evenly as fuel economy rises. The study subjects also failed to easily pick which cars would represent the biggest increase in fuel economy when the numbers were stated in miles per gallon.

It comes down to math: people thought going from 34 mpg to 50 mpg saved more gas than going from 18 to 28 mpg, when it's actually the latter boost that saves more--twice as much. When the numbers were expressed in gallons per mile, study subjects correctly figured out that 18 miles per gallon, or 5.5 gallons per 100 miles, is a lot less efficient than 28 mpg, or 3.6 gallons per 100 miles.

In a lesson for drivers of SUVs, Professor Larrick said "the reality that few people appreciate is that improving fuel efficiency from 10 to 20 mpg is actually a more significant savings than improving from 25 to 50 mpg for the same distance of driving."

The profs recommend the auto industry label cars for gas used over 10,000 miles driven. Do you think that's a better standard--and does the math make sense to you yet? Tell us in a comment below.

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