The U.S. Environmental Protection Agency National Vehicle and Fuel Emissions Laboratory and the California Air Resources Board confirm that when given the choice of idling for a few minutes or turning your car off, you should always choose the latter.

Tests comparing emissions over minute-long increments for restarted versus idled cars confirm: Idling produces more emissions. Over nine minutes, an idling car will emit double the pollutants of a car that is turned off and then restarted.

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Excerpted from:

Wake Up and Smell the Planet by Grist.org, edited by Brangien Davis, © 2007 Skipstone.