When idle, a vehicle uses about 1/5 to 7/10 of a gallon of gas per hour, while diesel vehicles use about one gallon per hour. The exact amount depends on the age and condition of the vehicle, with older vehicles in sub-par conditions consuming more fuel. Idling needlessly wastes fuel, increases maintenance costs of the vehicle and creates as much pollution as a moving vehicle.
Contrary to popular opinion, idling a car for longer than 10 seconds consumes more fuel than restarting the car. Also, the wear on a car's battery and starter that is induced by restarting the vehicle costs less than $10 a year, compared to about $70 to $650 in fuel consumed. Idling for about 10 minutes releases a pound of carbon dioxide, which is the leading contributor to global warming and damage to the ozone layer. These pollutants are also more likely to harm the driver when the car is sitting rather than moving. Before electronically controlled engines, idling for extended periods of time was done in cold weather to warm up the engines prior to driving and to heat up the cabin interior of the car. With electronically-controlled vehicles, this is no longer necessary, as cars can warm up without excessive wear by a few minutes of light driving.