Over 700 cities around the world have implemented bike sharing systems that allow people to make use of public bikes for short trips within the city.  The motivation is to reduce air pollution, noise and vehicular traffic congestion while providing people with the health benefits that come from daily exercise (which has been shown to decrease the costs of city-provided health services). The bikes can usually be used for free or for very low cost.

Oliver O’Brien, a researcher in the Geography Department of University College London has built a bike-share map that tracks the locations of bikes in the bike share systems of about 100 cities throughout the world. You can start with a global map and then click on the city of your choice to check out the more-or-less current state of the bike-sharing stations in the city. For example, here are the maps for Washington DC, New York