Cold weather starts! Nice to have a warm car with a clear windshield. I know the precise landmark in the 4 different directions from my house when I can feel hot air coming out of my heater - it was about 3 miles from my house with my Honda and 7 miles from my house with my diesel Jetta. VW specifically said NOT to idle the engine to warm the car.

That said, a good common sense rule about idling a car is "if you aren't in it, don't run the motor." I think we've all seen someone hanging out in a convenience store getting "stuff" while their car is idling outside.

I live near train tracks, so I turn my engine off when I see I'm going to be waiting for a long, slow freight train to pass by. I have, on occasion, turned off the engine at a long traffic light. (And, having a stick shift, I can sit in neutral which runs the engine slower). But turning the engine off in traffic isn't always safe, so I think the best rule of thumb is the aforementioned - turn off the engine as you get out of th car.