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, especially in densely populated European cities. Cycling is widely regarded as an effective and efficient mode of transportation optimal for short to moderate distances. Bicycles provide numerous possible 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 and noise pollution, reduced greenhouse gas emissions, and greatly reduced traffic congestion.