Miles-Per-Gallon Math
When a 2-miles-per-gallon improvement is better than improving by 16 miles per gallon.
Say you’ve got two cars in your garage. One of them gets 34
miles per gallon; the other gets only 12. You drive both cars 10,000 miles in
the course of a year.
Would you save more gas by a) trading in the 34-miles-per-gallon
car for one that gets 50 miles per gallon, or by b) trading in the 12-miles-per-gallon
car for one that gets 14 miles per gallon?
New
experiments suggest that people tend to pick a). After all, a 16-miles-per-gallon
improvement seems better than an improvement of just 2 miles per gallon.
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The right answer is b).
If you start driving the 50-miles-per-gallon car instead of
the 34-miles-per-gallon car, you’ll save 94.1 gallons of gas per year.
If you start driving the 14-miles-per-gallon car instead of
the 12-miles-per-gallon car, you’ll save 119 gallons per year.
The math is simple arithmetic. Divide the total number of
miles driven (10,000) by the miles per gallon to get the total gallons used to
drive that distance. For 12 miles per gallon, the answer is 833. For 14 miles
per gallon, it’s 714.
The fact that people guess a) rather than b) suggests that
miles per gallon isn’t a useful metric for describing a vehicle’s gas
consumption, say the researchers who did the recent experiments. A much more
direct way to measure fuel consumption is an estimate of the amount of gas required
to travel a given distance.
Such a number would also make it easier to convey just how
much could be saved by moving closer to work or taking public transportation.
And it renders the difference between a 12-miles-per-gallon SUV and a 50-miles-per-gallon
hybrid more impressive, making it clear just how much fuel gas guzzlers are using.
It takes 833 gallons to travel 10,000 miles in the former vehicle; it only
takes 200 gallons to go 10,000 miles in the latter.
