A snowmobile, also known as a Ski-Doo, snowmachine, sled, motor sled, motor sledge, skimobile, or snow scooter, is a motorized vehicle designed for winter travel and recreation on snow. It is designed to be operated on snow and ice and does not require a road or trail, but most are driven on open terrain or trails. Snowmobiling is a sport that many people have taken on as a serious hobby. Older snowmobiles could generally accommodate two people; however, most snowmobiles manufactured since the 1990s have been designed to only accommodate one person. Snowmobiles built with the ability to accommodate two people are referred to as "2-up" snowmobiles or "touring" models and make up an extremely small share of the market. Most snowmobiles do not have any enclosures, except for a windshield, and their engines normally drive a continuous track at the rear. Skis at the front provide directional control. Early snowmobiles used simple rubber tracks, but modern snowmobiles' tracks are usually made of a Kevlar composite construction. The earliest snowmobiles were powered by readily available industrial four-stroke, air-cooled engines. These would quickly be replaced by lighter and more powerful two-stroke gasoline internal combustion engines and since the mid-2000s four-stroke engines had re-entered the market. The second half of the 20th century saw the rise of recreational snowmobiling, whose riders are called snowmobilers, sledders, or slednecks. Recreational riding is known as snowcross/racing, trail riding, freestyle, boondocking, ditchbanging and grass drags. In the summertime snowmobilers can drag race on grass, asphalt strips, or even across water (as in snowmobile skipping). Snowmobiles are sometimes modified to compete in long-distance off-road races. Legality Depending on jurisdiction, there may be penalties for driving outside permitted areas, without an approved helmet, without a driver's license, with an unregistered snowmobile, or while under the influence of alcohol or other substances. There may also be regulations regarding noise and wildlife. Driver's license In some jurisdictions, a driver's license is required to operate a snowmobile. A specific snowmobile driver's license is required in, for example, Norway and Sweden. In Finland, a snowmobile driver's license is not required if the driver already has another type of appropriate driver's license (for example car or tractor). Early history In 1911 a 24-year-old, Harold J. Kalenze (pronounced Collins), patented the Vehicle Propeller in Brandon, Manitoba, Canada. In 1915 Ray H. Muscott of Waters, Michigan, received the Canadian patent for his motor sleigh, or