Duke professors challenge term 'miles per gallon'

Some Duke professors are challenging the conventional "miles per gallon" terminology employed by the automobile industry.

Researchers with Duke's Fuqua School of Business say that posting a vehicle's fuel efficiency in "gallons per mile" rather than "miles per gallon" would help motorists make better decisions when buying a new car.

The study will appear in the June 20 issue of Science magazine. It was inspired by a debate professors Richard Larrick and Jack Soll had while carpooling in a hybrid car, according to a Duke press release.

The two management professors ran experiments showing current "miles per gallon" terminology led consumers to think fuel consumption goes down at an even rate as efficiency improves.

For example, most people said an increase from 34 to 50 mpg saved more gas over 10,000 miles than an increase from 18 to 28 mpg, even though the latter saves twice as much gas, according to the Duke press release. (Going from 34 to 50 mpg saves 94 gallons; but going from 18 to 28 mpg saves 198 gallons).

These mistaken impressions were corrected, however, when participants were presented with fuel efficiency expressed in gallons used per 100 miles. Viewed this way, 18 mpg becomes 5.5 gallons per 100 miles, and 28 mpg is 3.6 gallons per 100 miles -- an $8 difference today.