The penalty for speeding: A loss in fuel economy

You know that driving at 75 mph rather than 55 wastes gas, but how much? We did the math, driving a steady 55, 65, and 75 mph in a Honda Accord, a Toyota RAV4, and three versions of a Ford Fusion. The penalty for speeding, even in those relatively fuel efficient cars: a loss of up to 14 mpg.

True, driving 200 miles at 75 instead of 55 shaves an hour off your trip. But in the cars we used, it also wastes 1½ to 2 gallons and costs about $5 to $7. For every thousand miles at 75 mph, you're increasing carbon footprint by 7 to 10 gallons and throwing away about $30.

Need more motivation? High speeds increase the likelihood of a crash and slash the odds of surviving one, says the Insurance Institute for Highway Safety.

Other gas-saving tips. Drive smoothly when possible, avoiding hard acceleration and hard braking. Combine short trips to avoid driving with a cold engine, and keep tires properly inflated. Turn the car off if it will be idling for more than about 30 seconds.