A drop of gas info could save gallons

By Daniel Squadron

This holiday season, millions of Americans will take to the road — and spend literally billions of dollars on fuel. We’ll be reminded once again that buying a car is not just a one-time expenditure. The cost adds up: a few more dollars every time you fill up at the pump.

Of course, it’s not just economics. Between global warming and the other negative effects of burning fuel, a growing number of consumers worry about the environmental impact as well.

Right now, consumers use the standard miles-per-gallon calculation to compare fuel efficiency. And it seems pretty straightforward: it’s obvious that a Hummer (16 M.P.G.) will burn a lot more gas over time than a Prius (46 M.P.G.).

But when consumers try to compare the relative efficiency, as they usually do, the miles-per-gallon measurement falls short. For example, take this pop quiz: two families want to save money on gas. Family A upgrades from a 10 M.P.G. to a 15 M.P.G. light truck. Family B upgrades from a 25 M.P.G. to a 45 M.P.G. sedan. Over the next 1,000 miles, who has saved more gas?

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