The Underground line has hump-backed stations which allow trains to store gravitational potential energy as they arrive and to then use this energy as they leave the stations. The stations are on top of small hills, or humps. As the train travels up the hill to the station its weight helps it to slow down. As the train leaves the station it travels down the hill, with gravity helping the train to speed up. This saves 5% energy and makes the trains run 9% faster. Each new platform built for the Victoria Line is 132.6 metres long. Around 200 million people use the Victoria line each year.