A snowmobile is a land vehicle powered by a single caterpillar drive wheel with skis on the sides for steering. They are designed to be operated on snow or ice, without requiring any type of road. Most snowmobiles are powered by a two-stroke engine, although four-stroke cycle engines are becoming more and more popular. Although not designed for it, snowmobiles can even be driven through the top layer of water if the speed is high enough.