Mile-per-gallon ratings may mislead
WASHINGTON (AP) - June 18, 2008 Strange as it may sound, rating cars at gallons-per-mile may be
more useful, say a pair of university researchers.
Richard Larrick and Jack Soll got to discussing fuel efficiency
while carpooling to work at Duke University's Fuqua School of
Business.
The professors study how people perceive things and decided to
look into the auto efficiency ratings and what they tell consumers.
The result is a paper called "The MPG Illusion," appearing
Friday in the journal Science.
In essence, they say, don't turn your nose up at what may seem
like a small gain, it can still mean big savings at the pump.
Not everyone is a good candidate for a tiny car, Larrick
explained, a family of five or six needs a larger vehicle. But
moving to even a slightly more efficient large car can be a big
saving, he said.
"We realized improving low mpgs is where the big bang is,"
Larrick said in a telephone interview. "But we realized that
people were not going to understand that."
He stressed that they are not advocating buying inefficient
cars, but rather pointing out that those are the ones that need to
be replaced, even if the extra miles per gallon seem small.
"There are significant savings to be had by improving
efficiency by even two or three miles per gallon on inefficient
cars, but because we communicate in miles per gallon, that savings
is not immediately evident to consumers," said Soll.
Jack Gillis of the Consumer Federation of America called their
paper "extraordinarily profound in its simplicity."
The report shows that people with inefficient cars, who may feel
they have no options, can experience substantial savings by just
moderately increasing their fuel efficiency, Gillis said.
"I am convinced that the average, extraordinarily frustrated,
owner of a fuel inefficient car has no idea that making a small
improvement will save more money and will save the environment"
more than a larger improvement in a more efficient car, Gillis
said.
So why does it help to look at gallons per mile instead?
Well, that tells you how much gasoline is used or saved over a
given distance, say a year's driving of 10,000 miles.
Gillis calculated that at $4-a-gallon, over 10,000 miles, an
improvement from 12 mpg to 13 mpg would save $256. For the owner of
a 33 mpg car to save that much, mileage would have to go up to 40
mpg, he said.
Here's how it works.
A couple drives a 25 mpg sedan. They trade it for a 50 mpg
hybrid, a 25 mpg improvement.
A family with mom, dad and three kids has a 10 mpg SUV to haul
everyone around. They trade it for a 20 mpg station wagon, a 10 mpg
improvement.
Sounds like the couple did better, at least in miles per gallon.
But lets look at gallons per miles.
At 25 mpg the couple burned 400 gallons over a year and their
new 50 mpg hybrid cuts that to 200 gallons. They save 200 gallons.
At 10 mpg the family's SUV burns 1,000 gallons of gas a year. At
20 mpg the station wagon burns 500 gallons - they save 500 gallons,
much better than the couple.
Would it be better for everybody to switch to the most efficient
car? Sure, but not every family will fit in it.
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On the Net:
Science: http://www.sciencemag.org