I've often wondered about this question while waiting in the nursery school carpool pickup line (where I can wait quite a while …). First let’s talk about what idling is. In high school, “idling” meant you were hanging out in the hallways when you should have been in class, an infraction I was accused of many a time. In terms of your car, “idling” means putting the car in park and leaving it running when you could otherwise be turning it off — in a drive-thru, for instance, or waiting at the train station to pick up your friend.

So, now that we know what idling is — better to idle or to turn off your car? The answer is the same one the assistant principal had for you all those years ago — better not to idle. The rule of thumb used by California’s Consumer Energy Center is this: If you’re going to be idling more than 10 seconds, turn off your car. That’s because when you’re idling, you’re still releasing harmful emissions into the air just like when you’re driving, except when you’re idling, you’re getting zero miles per gallon. And contrary to popular belief, it doesn’t take more gas to shut down and restart your car than it does to leave it idling for a few minutes. It will save you money to shut off your car rather than idle — up to 19 percent, according to Edmunds.com.

Interestingly, one of the ways hybrid cars save energy is by automatically shutting off at red lights or when otherwise stopped. In fact, since this start-stop technology was invented, some car companies, including BMW, are talking about adopting the same technology in all of their cars, which could greatly reduce the amount of air pollution that is caused by idling cars.

While we’re at it, let’s dispel some other idling myths: Do you like to warm up your car for a few minutes in the winter before you drive it? My husband, who’s from Chicago, introduced me to the world of remote starters. See, in Chicago, where’s it’s often in the teens and single digits when it’s time to head out for work, everyone has remote starters to warm up their cars before they get in them. And I’m not going to lie — it’s so much nicer getting into a warm and toasty car rather than a stone-cold one. But warming up your car for five or 10 minutes is totally unnecessary to actually drive it. All you’re doing is wasting gas and wasting time. As long as you’re not accelerating too fast (such as turning onto a highway as you turn out of your driveway), starting your car, waiting a few seconds, and driving it immediately, but gently, is the way to go — literally.

What about revving your car’s engine when you start it? Also unnecessary. It’s actually a bad idea when your car’s engine is cold and its parts haven’t been lubricated with oil yet.

Well, there you have it. So don’t get caught idling in the halls … and especially not on the streets.

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