Wikipedia:Very good articles/Victoria line
The Victoria line is part of the London Underground network. It is a deep-level underground metro line that runs from Brixton in the south of London to the Walthamstow Central in the north-east. It started running in 1968. On the Tube map it is shown with a light blue colour. It is the fourth busiest line on the London Underground network. It is the only line on the Underground, other than the two-stop Waterloo & City line, which is completely underground. The only section of track to come above ground is the route to the depot from Seven Sisters to Northumberland Park.
The 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. 183 million people use the Victoria line each year.