Once the acceptance of bicycle transportation reaches a critical mass, private development can seize the opportunity. In Berlin and three other German cities, Deutsche Bahn, the national railway, has established an innovative form of bicycle rental program named Call-A-Bike. D.B. deployed several thousand bikes built to withstand the demands of city use, which can be found on many busy street corners. After establishing an account, a member can find a locked D.B. bike, send a text message to get an unlocking code, and pedal off around the city at a rate of 7 Euro cents per minute. Whenever you get to your destination, you lock up the bike for the next user and leave Call-A-Bike a voice message with the location of the bike for tracking purposes.