More fuel economy tips

- The Department of Energy's website suggests that turning off the air conditioner may improve fuel economy when driving at speeds under 40 mph.

- It's more fuel efficient to restart the car than to leave the engine idling. (The 2008 Toyota Prius engine, among other things, shuts off automatically during stops that last more than a few seconds. )

- You can optimize your fuel economy on the highway by putting your car into overdrive, typically the transmission's highest gear. This will allow your engine to run at a lower level of revolutions per minute, and use less energy. According to the Department of Energy, when overdrive gearing is used, "your car's engine speed goes down. This saves gas and reduces engine wear."

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- Inflating your tires beyond the recommended level will reduce the portion of the tire in contact with the road and the resistance between the tires and the road, but over-inflating them can make for a rocky ride. Popular Mechanics has also road tested this theory and concluded that the gas mileage doesn't improve. The difference occurs when under-inflated tires are pumped to proper levels. In fact, the Department of Energy estimates that this simple fill up can improve your gas mileage by 3.3 percent.