has over 20,000 bikes in its rental fleet in Paris.  Read about Velib on wikipedia - this system is worth studying for many reasons, reasons besides transportation. Because the system is so large, problems show up fast.   For example, rental stations at higher elevations around Paris are depleted of bikes because it is easier to ride downhill, and then leave the rental bike at a lower elevation and use another form of transport back up to the higher elevation.   So the system is changing pricing in order to incentivize riders to return bikes to the higher elevation stations.