Cycling, also called bicycling or biking, is the use of bicycles for transport, recreation, or for sport. Persons engaged in cycling are referred to as "cyclists" or, less commonly, as "bicyclists". Apart from two-wheeled bicycles, "cycling" also includes the riding of unicycles, tricycles, quadracycles, and similar human-powered vehicles (HPVs). Bicycles were introduced in the 19th century and now number about one billion worldwide. They are the principal means of transportation in many parts of the world. Cycling is widely regarded as a very effective and efficient mode of transportation optimal for short to moderate distances. Bicycles provide numerous benefits by comparison with motor vehicles, including the sustained physical exercise necessarily involved in cycling, that cycling involves a reduced consumption of fossil fuels, less air or noise pollution, much reduced traffic congestion, easier parking, greater maneuverability, and access to both roads and paths. The advantages al...