Although motorization has increased speed and load capacity, many forms of human-powered transport remain popular for reasons of lower cost, leisure, physical exercise and environmentalism. Human-powered transport is sometimes the only type available, especially in underdeveloped or inaccessible regions.
In the transport sector, walking and cycling transport are often grouped together under active transport, comparing to such other transport forms as public transport, or freight transport.
A sled, sledge, or sleigh is a land vehicle with a smooth underside or possessing a separate body supported by two or more smooth, relatively narrow, longitudinal runners that travels by sliding across a surface. Most sleds are used on surfaces with low friction, such as snow or ice. In some cases, sleds may be used on mud, grass, or even smooth stones. They may be used to transport passengers, cargo, or both. Shades of meaning differentiating the three terms often reflect regional variations depending on historical uses and prevailing climate.
In Britain the three terms are generally quite similar in meaning, although sledge usually refers to a smaller sled, used mostly for freight, one that can generally transport no more than one or two persons with only a limited amount of cargo. Sledges may be pulled by dogs or other smaller animals, although confusingly a sledge pulled by a dog in British English is often referred to as a dog-sled. A small recreational sled, pulled by humans, can also be referred to as a sledge. Sleigh (pronounced "slay") remains largely a synonym for sled regardless of its capacity (and similarly in Canada).
In American usage sled remains the general term but often implies a smaller device, often for recreational use. Sledge implies a heavier sled used for moving freight or massive objects (syn. "stone boat"), while sleigh typically refers to a moderate- to large-sized, usually open-topped vehicle equipped with one or more passenger seats, essentially a cold-season alternative to a carriage or wagon, typically drawn by horses or (at least in the Santa Claus legend or in reference to Scandinavia) by reindeer.