With gas prices heading north of $4 a gallon, many people and companies are thinking of switching to a more fuel efficient vehicle.
Lets say, like many American families, you are a two car family with an SUV and a full sized sedan. You'd like to replace one of them to save on the cost of fuel. You decide to either exchange the 25 mpg sedan for a 50 mpg Prius, or the 10 mpg SUV for a 20 mpg station wagon.
Which one should you choose? As a new article in Science magazine shows, if you thought switching the sedan for the prius saved more gas you'd be in agreement with most Americans - and you'd be absolutely wrong.
The more useful metric, the authors of this article ($ubscription) argue, is one of gallons per mile.
If you drive 10,000 miles per year, your 25 mpg car would take 400 gallons (10000miles/25mpg). The 50 mpg Prius would take 200 gallons, a savings of 200 gallons per year (or $800).
Your 10 mpg SUV needs 1,000 gallons for the year. Switching to a 20 mpg car would reduce that to 500 gallons per year, a 500 gallon ($2,000) savings. Of course, switching from the SUV to the Prius would save you a whopping 800 gallons a year, but that may not always be an option.
Therefore, if you're considering buying a car, forget the mpg number, and instead figure out how many gallons it would take for you to drive it 10,000 miles - you'll be able to figure out your fuel savings much more easily.