Car buyers confused about fuel economy measures say US researchers
Sat 21 June 2008
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Expressing a vehicle's fuel efficiency in terms of 'gallons per mile' rather than 'miles per gallon' would help consumers make better decisions about which car to purchase and about environmental impacts according to new research from a US university.
Research by Richard Larrick and Jack Soll of Duke University’s Fuqua School of Business was published in the June issue of Science magazine. Their research was inspired by debates they had while car-pooling in a hybrid car. The two management professors ran a series of experiments showing that the current standard, miles per gallon (mpg), leads consumers to believe that fuel consumption is reduced at an even rate as efficiency improves. People presented with a series of car choices in which fuel efficiency was defined in miles per gallon were not able to easily identify the choice that would result in the greatest gains in fuel efficiency.
For example, they said, most people ranked an improvement from 34 to 50 mpg as saving more fuel over 10,000 miles than an improvement from 18 to 28 mpg, even though the latter saves twice as much. (94 gallons compared with 198 gallons).
When participants were presented with fuel efficiency expressed in gallons used per 100 miles, their mistaken impressions were corrected. (When viewed this way, 18 mpg becomes 5.5 gallons per 100 miles, and 28 mpg is 3.6 gallons per 100 miles. The improvement from 34 to 50 mpg reduces fuel consumption from 3 to 2 gallons over 100 miles and saves only half as much fuel and money.)
Richard Larrick said: “The reality that few people appreciate is that improving fuel efficiency from 10 to 20 mpg is actually a more significant saving than improving from 25 to 50 mpg for the same distance of driving.”
Jack Soll said: “For families and other owners of more than one type of vehicle, the greatest fuel saving often comes from improving the efficiency of the less efficient car. When fuel efficiency is expressed as gallons per 100 miles it becomes clear which combination of cars will save a family the most gas".
The researchers suggest that consumer publications and car manufacturers should list efficiency in terms of gallons per 10,000 miles driven rather than in terms of miles per gallon.
“This measure makes it easy to see how much gas one might use in a given year of driving and how much gas, and money, can be saved by opting for a car with greater efficiency,” Larrick said.
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