When to turn off your engine

This post is by Mel Peffers, Air Quality Project Manager at Environmental Defense.

In the winter, many people idle their car engine after starting it up because they think it needs time to warm up. Not true! Today's fuel-injected engines don't need a warm-up period, and idling for long periods can lead to excessive engine wear.

Worse, cars idling for more than 10 seconds use more gas and create more global warming pollution than simply restarting the engine. Surprised? It's true - the 10-second rule has been proven empirically.

The 10-second rule was originally published on the Canadian Office of Energy Efficiency's Idle-Free Zone webpage. Their results were replicated by the American Society of Mechanical Engineers, which found that restarting uses the same amount of fuel as idling with the air conditioner on for 6 seconds.

Diesel engines can use more fuel idling than moving a vehicle - as much as four times more (see this study on school buses in Los Angeles, and also this EPA study with similar findings). Besides contributing to global warming, diesel engine emissions can cause a host of health problems: asthma attacks, impaired lung function, heart problems, and even death.

Idling is a significant problem in large cities like New York and Los Angeles, where people are often stuck in traffic. A car in gridlock emits up to three times the pollution as one in free-flowing driving conditions.

Environmental Defense is working with the City of New York on reducing traffic congestion. We're also working with Mayor Bloomberg on tougher enforcement of the existing idling law, which has been in effect for five years. Plus, we're working on a no-idling policy for school buses in Texas, and on Truck Stop Electrification (TSE) expansion, so truckers won't need to idle overnight while sleeping. And our GreenFleet initiative helps fleet owners reduce emissions.

Avoiding pollution and engine wear aren't the only benefits of not idling. You also can save gas and money. Here are a couple of studies that demonstrate this:

Edmunds.com: "... you can drastically improve your gas mileage."

Homemade Hybrid: "I kicked the idling habit and saved a gallon of gas per tank ..."

With this cost-of-idling worksheet from Argonne National Laboratories, you can calculate the savings for your own vehicle. For more tips on clean driving, visit Car Talk's Driving Tips for Tree-Huggers.

Not idling is good for the environment, good for your wallet, good for engines, and good for health. Everyone wins by simply turning off an idling engine.