Prius people have reported the same problem (which is no surprise since it's essentially the same drive system). The answer, at least in my case, is decent snow tires. The system will only shut down completely if it has absolutely no traction to work with. If the tires can't bite (which they can't since they aren't designed for it) you get virtually no power. My Blizzaks have kept me mobile despite my poorly-plowed apartment and work parking lots and living at the top of a huge hill. You will be able to stop in the snow, too, which is a nice touch.