Don't wait idly by. Rev up for the environment.

When you pull up to a stop light, should you cut the engine? Should you warm up your car before pulling out of the driveway? According to anti-idling advocates, and contrary to conventional wisdom (i.e., what I was taught), the answers are yes and no.

Myth 3: Repeatedly restarting your car is hard on the engine and quickly drains the battery.
Wrong. Frequently restarting your engine does negligible damage to the engine and does not drain modern batteries excessively. In fact, the opposite is true; idling an engine forces it to operate in a very inefficient and gasoline-rich mode that, over time, can degrade the engine’s performance and reduce mileage.

According to the site, and a quick scan of the google results, if you are idling for more than 10 seconds, it is best to turn off the engine. It is better for your engine, the environment, and your wallet. They also say the best way to warm up your car is by driving it (that you should start driving within 30 seconds of starting the car, even on really cold days).