From Ideal Bite
The sound of an idling car. It may seem like idling uses less gas than turning your car off and on again, but it usually doesn't, and the pollution idling causes is a lot less entertaining than betting on which Idol winner is gonna get dropped by their record label next.
Less air (and ear) pollution. An idling car creates twice the emissions of a car in motion.
Saving money. Idling 15 min per weekday can cost you up to $100 in wasted gas over the course of a year.
Saving oil. American drivers use more than 2 bil gal of fuel each year while idling.
School parking lots are notorious for idlers, so most of us probably sucked down a lotta fumes waiting for our parents to pick us up after school, except for Jenifer, who had to walk home...both ways, uphill...in the snow...
Turn your car off if you're gonna stay put for more than 10 seconds, and BTW: Driving warms up your car way faster than idling.
EPA - resources for starting an idling-reduction program at your kid's school district.