If you can get somewhere in 15 minutes by jogging or 30 minutes walking, then get a move on! It is not only good for your health but great for the planet as well!
I have started using the 15/30 rule to decide whether I should drive or walk somewhere. If I can jog there in 15 minutes, or walk there in 30, then I'm lacing up and hitting the sidewalk. If it's the summer or a particularly nice area that I am venturing, I will definately walk much further. An hour long walk on sunny, warm day is such a treat, but the 15/30 rule gets me walking places I would have driven in the past.
Even in the -25 degree weather I manage to bundle up and get places with little hassle. Your movement will generate internal body heat to keep you warm and you'll be at your destination in less time then it would take for your car to warm up.
I am fortunate to live a 10 minute walk from downtown Calgary, and thanks to the great pathway systems, I am able to walk most places without crossing major roads. I realize not everyone has this luxury, and living in the suburbs may mean you are forced to drive more. But, convenient retail establishments are popping up closer and closer to residential areas, yet we still see so many people driving to the Starbucks around the corner or to pick up a bottle of wine at the local liquor store. I know I used to be guilty of the later; 'I couldn't possibly walk for 15 minutes there and 15 minutes back for that bottle of wine, I need it now'. We are busy people!
Take that little bit of extra time for yourself. It will improve your mood and help the environment at the same time.