There's a time to keep that engine running - it's when you're in motion.

Once gas is in the tank, we tend not to think about what we're doing with it until we run out again. When we’re sitting in our cars with the motor humming along for five or ten minutes at a time—waiting for kids to get ready for school, finishing a phone call, or stuck in a traffic snarl—we tend not to think about the effect that might have on the environment, nearby people, and our own pocketbooks. Particulate grunge, when inhaled, accumulates only in imperceptible increments, so without a statistician nearby, it's easy to forget the health impacts of our behavior.

Idling has become an object of increased scrutiny in the recent past, as evidence of the damage it can cause has mounted. No idling signs are essential tools to remind drivers to turn their engines off when they're not in motion, saving money and public health.