What activity wastes gasoline, costs money, produces pollutants, and yet doesn't get you anywhere? Idling! And yet, every year, Americans waste 3 billion gallons of fuel by idling their vehicles.

Idling is running a vehicle any time that it's not moving. In this condition, the car's fuel economy is exactly zero miles per gallon. Although many people think that restarting the engine too often will wear out the starter, that idea is just an "old husband's tale." In fact, idling places unnecessary wear-and-tear on the engine, and many manufacturers discourage it.

Although drivers can't avoid some amount of idling, such as being stuck in traffic, you can limit it in many situations. Drivers of passenger cars (light-duty vehicles) should turn off their engines if they are stopped for more than 30 seconds. Choosing to walk into restaurants and banks rather than using the drive-through will certainly help improve fuel economy, reduce emissions, and enhance your well-being. In addition, purchasing a hybrid electric vehicle that turns off its engine when stopped can help make not idling second nature. Locally based campaigns, working with Clean Cities coalitions, have reduced idling nationwide, including San Antonio's Green Patrol and Idle Free Utah.

Heavy-duty vehicles, such as buses and trucks, cause even more pollution when they idle than light-duty ones. Most heavy-duty vehicles run on diesel fuel and produce many more pollutants than gasoline vehicles. Although newer diesel vehicles are cleaner than ever before, older vehicles emit large amounts of carbon monoxide (CO), oxides of nitrogen (NOx), particulate matter (PM), volatile organic compounds (VOCs), hydrocarbons (HC), and oxides of sulfur (SOx).

These pollutants worsen cardiovascular and respiratory problems, such as heart disease, asthma, and bronchitis. It is particularly important to reduce diesel pollution near schools, in urban regions, and in economically disadvantaged areas. Children, whose bodies are still developing, are far more susceptible than adults to the damage pollution causes. Urban and low-income areas often have more trucks and buses on their streets than suburban regions, exposing residents to more overall pollution.

Reducing idling in heavy-duty vehicles can be a bit more complicated than for light-duty, but is still possible. School buses and long-haul trucks are two of the most common heavy-duty vehicles that regularly idle.

School buses often idle outside of schools while the driver waits for students to finish class. However, drivers should turn off the engine as soon as they finish loading and unloading passengers and limit their warm-up times to 5 minutes or less. In cold weather, buses can use heaters that do not run off the engine. These heaters use only 1 cup of fuel per hour in contrast to the ½ gallon per hour used for idling. Even a little bit can make a big difference!

With the help of their local Clean Cities coordinator, 435 Utah bus drivers pledged to reduce idling by 5 minutes a day, saving over 3,000 gallons of fuel a year (PDF 309 KB) Download Adobe Reader.

If you're interested in reducing idling at your neighborhood school, the U.S. Environmental Protection Agency has a Fuel Savings Calculator and an Idle-Reduction Campaign Kit available through their Clean School Bus USA program.

Long-haul trucks pose even more complex issues, as truckers often idle vehicles to keep themselves comfortable while they sleep or during federally mandated rest periods. However, truckers can install auxiliary power units, which mount on the truck and provide heating and cooling without running the engine. In addition, some truck stops have electrification units that allow truckers to plug in their vehicles and run the systems they need.

Thankfully, reducing idling is much simpler for most of us. Just remember: turn your key, be idle free!

Shannon Brescher Shea
Shannon Brescher Shea (shannon.shea@science.doe.gov) is the social media manager and senior writer/editor in the Office of Science’s Office of Communication and Public Affairs.
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