Vehicle Idling
Vehicle idling gets 0 miles per gallon! Idling wastes gas, pollutes the air, and gets you nowhere.
Think about this: if your mom picks you up from school and idles her car for ten minutes, the tailpipe emissions hang out in the parking lot (where kids breathe that air) until it can be dispersed. If she drove for ten minutes, that air pollution would be spread out over, say, five miles or so. Better to turn off your engine and do what you can to avoid a long wait time.