Idling of cars costs money, consumes energy, and pollutes the air. But, when winter temperatures dip below freezing, many Americans intentionally idle their cars for long periods of time. The reasons why were discussed this month in detail in a series of articles by Chris Mooney*, who is leading the Washington Post’s new energy and environment online section.

Across the country, idling vehicles account for an estimated 10.6 billion gallons of gasoline use and 1.6% of total greenhouse gases emissions. Furthermore, idling can produce significant amounts of other air pollutants including volatile organic compounds (VOCs), carbon monoxide, NOx, and particulate matter (PM). These pollutants have all been identified as threats to human health. In the case of particulate matter, health impacts include asthma and other respiratory illnesses, lung cancer and cardiopulmonary mortality. Globally, an estimated 800,000 early deaths occur each year as the result of combustion-related emissions (both particulate matter and ozone).

According to researchers at Vanderbilt University, the average person will spend 4.2 minutes per day idling their car in order to warm it up. This behaviour represents about 25% of the estimated per capita idling time in the United States. (Note: these data are from a survey that was originally conducted in 2007 and so the exact numbers may have changed somewhat over the last 7 years).

In his recent series, Mooney explored reasons why people might or might not choose to ide their cars in the winter for longer than the 30 seconds recommended by the U.S. Department of Energy, concluding that winter idling of vehicles is “the biggest winter energy myth” that stems from a history of misconceptions:

“Like many misconceptions, the idea behind winter car idling begins with a kernel of truth. Cars do get worse fuel economy when it's really cold out -- they are at least 12 percent less fuel efficient, according to Environmental Protection Agency and Energy Department. And it does take longer for the engine to warm up and reach an optimal driving temperature in cold weather.

Moreover, older cars -- which relied on carburetors as a crucial engine component -- did need to warm up to work well, according to several auto industry experts. Without warming up, the carburetor would not necessarily be able to get the right mix of air and fuel in the engine -- and the car might stall out. During the 1980s and into the early 1990s, however, the auto industry did away with carburetors in favor of electronic fuel injection, which uses sensors to supply fuel to the engine and get the right air and fuel mix. This makes the problem of warming up the car before driving irrelevant, because the sensors monitor and adjust to temperature conditions.

Idling in winter thus has no benefit to your (presumably modern) car. Auto experts today say that you should warm up the car no more than 30 seconds before you start driving in winter. "The engine will warm up faster being driven," the EPA and DOE explain. Indeed, it is better to turn your engine off and start it again than to leave it idling. (As many readers pointed out after this post was first published, it's always important to be careful driving in winter, and clear your windshield of any ice.)”

But, in his follow-up article, Mooney notes that people often idle their cars in the winter for reasons that have nothing to do with these misconceptions but rather are primarily focused on safety and comfort:

“Perhaps the greatest volume of responses [from readers to the initial article on idling in the winter] came from people saying they could care less about energy concerns -- they idle their cars not for engine reasons, but to help defrost them and remove ice so that they can drive safely. That's not the focus of government agencies in this regard, but it is clearly a highly defensible use of idling.”

According to the U.S. Department of Energy, “the best way to warm up a vehicle is to drive it. No more than 30 seconds of idling on winter days is needed. Anything more simply wastes fuel and increases emissions.” But, there are many reasons why Americans might not follow this advice.

Photo Credit:

1. Photo of cars parked in the snow by newsanek exists in the public domain.

2. Table from Carrico, et. al. “Costly myths: An analysis of idling beliefs and behavior in personal motor vehicles” August 2009 <link>

*Melissa C. Lott was a guest writer on Chris Mooney and Sheril Kirshenbaum’s blog “The Intersection” at Discover Magazine in 2010.