I've known for a while that drivers who speed reduce their cars' gas mileage. But until recently, it seemed like a minor concern. With gas now costing more than $3 per gallon, it's become a lot more prominent in my thoughts. But it seems I'm in the minority on this.

In an unscientific AOL survey about how greatly gas mileage influences how fast people drive, 40% of the more than 140,000 respondents said "not at all," while 35% said "a little," and only 24% said "a lot." With the price of gas nearly twice its recent levels, how can drivers be so blithe? I'm guessing that most people just don't know how driving speed affects mileage. Let me shed some light on the matter.

According to a CNNMoney story by Peter Valdes-Dapena, "You can get 35% better fuel mileage out of your current vehicle by using a device most drivers already have. That would be your right foot." 35%! And it's not just about slowing down on the highway: "If you want a big gain in fuel mileage . you need to seriously lay off the pedals when driving around town. Accelerating more slowly away from green lights and stopping more gradually for red lights cut fuel consumption in Edmunds.com's tests by 35.4% for the Land Rover and 27.1% for the Mustang."

Let's be conservative, and assume that by slowing down your driving, you save 20% on fuel consumption. Let's also assume that it costs you $30 each week to fill your tank, for a total of $1,560 annually at current prices. If you knock 20% off that, you'll save $312. Knock off 35%, and your savings will top $500!

Here's some data from another source, MPGplus.com: "Keeping your highway speed at 55 mph can improve your gas mileage by as much as 25%, compared to 75 mph." And according to a Pocono Record article, "As a rule of thumb, each 5 mph over 60 mph is like paying an additional 20 cents per gallon for gas."

Learn more in these articles:

  • "Save Money on Gas." Some discount retailers such as Costco (NASDAQ:COST) and Wal-Mart (NYSE:WMT) sell extra-cheap gas.
  • "Make the Most of Rising Gas Prices." Consider hybrid vehicles such as the Toyota (NYSE:TM) Prius, the Honda (NYSE:HMC) Civic hybrid, the Ford (NYSE:F) Escape hybrid, GM's (NYSE:GM) Chevrolet Silverado hybrid, or the upcoming Nissan (NASDAQ:NSANY) Altima hybrid.

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Longtime Fool contributor Selena Maranjian owns shares of Costco and Wal-Mart. Costco is a Motley Fool Stock Advisor pick. Wal-Mart is an Motley Fool Inside Value pick. The Fool has a disclosure policy .