Cold winter weather can impact the fuel efficiency of your car, reducing it as much as 30 percent, according to the United States Department of Energy. The reason? Tires grip onto icy roads, seat warmers and defrosters run at full blast, and friction with the engine and transmission is greater in cold weather. One simple way to help improve efficiency is to keep your car parked in a warmer place, like a garage. And allow your car to "warm up" for no more than 30 seconds, which is all your car really needs in order to be ready to hit the road.