A snowmobile (or skidoo or snow scooter, often referred to by enthusiasts as a 'sled' and in the Canadian north and Alaska as a 'snowmachine') is a land vehicle propelled by one rubber track with ski(s) for steering. They are designed to be operated on snow and ice, and require no road or trail. Most snowmobiles are typically powered by two-stroke gasoline/petrol internal combustion engines. Four-stroke engines are becoming more and more popular in snowmobiles. Summertime occupations for snowmobile enthusiasts can also involve drag racing on grass or even asphalt strips. People who ride them commonly are known as snowmobilers. The three main types of riding are Motocross/racing, trail riding and mountain riding.