If you do have to drive, minimize the amount of time you sit in idle. Here’s a pretty easy general rule of thumb to remember: if you’re car’s running and you’re not moving, your gas mileage has dropped to zero mpg. I know for many of this, this is probably easier said than done, especially considering it’s pretty tough to avoid the daily rush hour traffic. However, if you find yourself stuck at a stoplight or know that it’s going to be a minute or two before you get moving again, turn off your car (assuming it’s safe to do so). Essentially, it takes about ten seconds worth of idling to use as much gasoline as it would to restart your car; this means if you’re going to be sitting at a stoplight for a minute or two, it’s best to shut the car off and save gasoline.

Don't Stand Idle On Gas Mileage
I almost never use drive-thru windows. It's not because I'm ecologically green or anything other socially responsible reason. I just usually don't feel like sitting there. The other day it was raining hard, and my wife suggested the drive-thru at Dunkin Donuts. We sat in our car, in line for 10 minutes, so my wife got to hear 10 minutes of griping from me about how much I hate sitting in the drive-thru line.

I may find them annoying, but there are some good reasons not to use the drive-thru. The most obvious are the carbon emissions your car spits out while you sit there, but there's another reason that hits closer to your wallet -- gas mileage. Every minute you sit with your engine idling means fewer miles per gallon. It may not seem like much, but it adds up. The myth that your car uses more gas to start itself up than idling for 10 minutes died a long time ago. In fact, after only 10 seconds of idling, most cars have used more gas than on start-up. Research done by the Canadian government shows that it's even worth turning your engine off at stop lights!

Every moment you spend idling your car's engine means time spent needlessly wasting gas, as well as rougher wear on your vehicle. So give it a rest, and avoid idling through your days.

One of the ways the much-praised Toyota Prius is able to achieve such impressive fuel economy is by having a computer cut out idling automatically: when you aren’t making headway, the gas engine shuts off. For regular cars, it doesn’t make sense to shut off the engine at every stop sign. (Even though Environmental Defense found that idling for more than 10 seconds wastes more gas than is required for startup.) But, you should certainly kill it when you are waiting for your date to finish getting ready. Or when your honey has to run into the bank to cash a check.

Overall, idling Americans burn 2.9 billion gallons of gas a year, worth around $78.2 billion, according to a recent report from Texas A&M. That doesn’t count the damage done to idling engines by incompletely burned fuel.