A trailer is an unpowered vehicle towed by a powered vehicle. It is commonly used for the transport of goods and materials. Sometimes recreational vehicles, travel trailers, or mobile homes with limited living facilities where people can camp or stay have been referred to as trailers. In earlier days, many such vehicles were towable trailers. United States In the United States, the term is sometimes used interchangeably with travel trailer and mobile home, varieties of trailers and manufactured housing designed for human habitation. Their origins lay in utility trailers built in a similar fashion to horse-drawn wagons. A trailer park is an area where mobile homes are placed for habitation. In the United States trailers ranging in size from single-axle dollies to 6-axle, high, long semi-trailers are commonplace. The latter, when towed as part of a tractor-trailer or "18-wheeler", carries a large percentage of the freight that travels over land in North America. Types Some trailers are made for personal (or small business) use with practically any powered vehicle having an appropriate hitch, but some trailers are part of large trucks called semi-trailer trucks for transportation of cargo. Enclosed toy trailers and motorcycle trailers can be towed by commonly accessible pickup truck or van, which generally require no special permit beyond a regular driver's license. Specialized trailers like open-air motorcycle trailers, bicycle trailers are much smaller, accessible to small automobiles, as are some simple trailers, have a drawbar and ride on a single axle. Other trailers, such as utility trailers and travel trailers or campers come in single and multiple axle varieties, to allow for varying sizes of tow vehicles. There also exist highly specialized trailers, such as genset trailers, pusher trailers and other types that are also used to power the towing vehicle. Others are custom-built to hold entire kitchens and other specialized equipment used by carnival vendors. There are also trailers for hauling boats. Trackless train Utility A utility trailer is an all purpose trailer to carry almost anything. It can be open or completely closed. Fixed Plant A Fixed Plant Trailer is a special purpose trailer built to carry units which usually are immobile such as large generators & pumps Bicycle A bicycle trailer is a motor less wheeled frame with a hitch system for transporting cargo by bicycle. Construction Toilets are usually provided separately. Construction trailers are mobile structures (trailers) used to accommodate temporary offices, dining