A snowmobile, also known as a motor sled, motor sled, skimobile, snowscooter, Ski-Doo, or snowmachine, is a motor vehicle designed for winter travel and snow recreation. It is designed for snow and ice activity and needs no path or track, but most are operated on open terrain or trails.Older snowmobiles typically could accommodate two people; however, most snowmobiles produced over the past 25 years were designed to accommodate only one person. Snowmobiles built with the ability to accommodate two people are known as "2-up" snowmobiles or "touring" models and represent an extremely small market share. Except for a windshield, snowmobiles have no enclosures and their engines normally drive a continuous track to the rear. Front-facing skis give directional control.Early snowmobiles used simple rubber tracks but the tracks of modern snowmobiles are usually made of a composite Kevlar construction. Snowmobiles were originally powered by internal combustion engines with two-stroke gasoline, and four-stroke engines have also entered the market since the mid-2000's. The second half of the 20th century saw the rise of snowmobiling for recreation, whose riders are called snowmobilers or sledders. Snowcross / racing, trail riding, freestyle, boondocking, ditchbanging, and grass drags are known as recreational riding. Snowmobilers will drag race on turf, asphalt roads, or even across water during the summertime (see Snowmobile Skipping).