The best way to warm up your car is to drive it
It's snowing here in Columbus, hooray! And, yep, it's cold. And, yep, the car is cold when you get into it. But did you know that the most efficient way to warm up your cold car engine is to actually drive it? Perhaps back in the olden days (you know, the 70s) it was advisable to let your car idle for 15 minutes on a cold day to get the engine oil flowing. But this is 2011, folks, and modern cars no longer need to sit in your driveway spewing exhaust while you sit inside finishing your cup of coffee. Don't believe me? Google it. Or ask the Car Talk brothers:
Unless it's below freezing, cars don't need to be warmed up at all. Driving them gently is the best warm up there is. If it's 25 degrees out, you might want to let it warm up for 30 seconds. If it's 10 degrees out, warm it up for a minute. If it's -10 degrees out, move somewhere warmer.
I see empty cars running in driveways all the time around here, and it makes me crazy. (Disclaimer: lots of things make me crazy.) And to be fair, I saw it in Portland, too, though not as much since it's not as cold there. But since Ohio has the worst air quality in the nation (again with the crazy), seems like there might be some sort of effort to raise awareness. Here, there and everywhere.