[image credit: Treehugger]
Idling a car to "warm it up" is wasteful and unnecessary
Most people believe that when it's cold outside, that you still need to idle a car for an extended period of time before driving off to avoid causing mechanical damage. That might have been true once upon a time (in the era of carburetors), but modern engines and modern oil only need a relatively short warm up period; after that, the best way to warm up a vehicle is to drive it (granted, if you're going to immediately jump on a highway and drive at high speeds, you might want to warm it up a bit more, but for regular low-speed driving, there's no need).
Solution: Give your car a 30-second warmup, and then drive
From a Department of Energy report: "Avoid idling. Think about it — idling gets you 0 miles per gallon. The best way to warm up a vehicle is to drive it. No more than 30 seconds of idling on winter days is needed. Anything more simply wastes fuel and increases emissions."