Bicycles were introduced in the 19th century and now number approximately one billion worldwide. They are the principal means of transportation in many parts of the world.
Bicycles provide numerous benefits in comparison with motor vehicles, including the sustained physical exercise involved in cycling, easier parking, increased maneuverability, and access to roads, bike paths and rural trails. Cycling also offers a reduced consumption of fossil fuels, less air or noise pollution, and much reduced traffic congestion. These lead to less financial cost to the user as well as to society at large (negligible damage to roads, less road area required). By fitting bicycle racks on the front of buses, transit agencies can significantly increase the areas they can serve.
Among the disadvantages of cycling are the requirement of bicycles (excepting tricycles or quadracycles) to be balanced by the rider in order to remain upright, the reduced protection in crashes in comparison to motor vehicles, often longer travel time (except in densely populated areas), vulnerability to weather conditions, difficulty in transporting passengers, and the fact that a basic level of fitness is required for cycling moderate to long distances.
In many countries, the most commonly used vehicle for road transport is a utility bicycle. These have frames with relaxed geometry, protecting the rider from shocks of the road and easing steering at low speeds. Utility bicycles tend to be equipped with accessories such as mudguards, pannier racks and lights, which extends their usefulness on a daily basis. As the bicycle is so effective as a means of transportation various companies have developed methods of carrying anything from the weekly shop to children on bicycles. Certain countries rely heavily on bicycles and their culture has developed around the bicycle as a primary form of transport. In Europe, Denmark and the Netherlands have the most bicycles per capita and most often use bicycles for everyday transport.
Road bikes tend to have a more upright shape and a shorter wheelbase, which make the bike more mobile but harder to ride slowly. The design, coupled with low or dropped handlebars, requires the rider to bend forward more, making use of stronger muscles (particularly the gluteus maximus) and reducing air resistance at high speed.