London Underground infrastructure Tube Programme, investigating replacing the trains for the Bakerloo and Piccadilly lines, is looking for trains with better energy conservation and regenerative braking. The Underground serves 270 stations. Fourteen Underground stations are outside Greater London, of which five (Amersham, Chalfont & Latimer, Chesham, and Chorleywood on the Metropolitan line and Epping on the Central line) are beyond the M25 London orbital motorway. The longest distance between two stations is between Chalfont & Latimer and Chesham on the Metropolitan line. The shortest distance between adjacent stations is the between Leicester Square and Covent Garden on the Piccadilly line. The station furthest
Urban rail in the United Kingdom Line, via tunnels through central London, with a branch to . It is the largest construction project in Europe. Crossrail will start a full service in 2018, taking over suburban services operated by Abellio Greater Anglia to Shenfield, Heathrow Connect to Heathrow Airport and First Great Western to Reading. Once opened, Crossrail will be one of three partially underground suburban rail networks in the United Kingdom as the network cannot be classed as a Metro system like the London Underground or the Glasgow Subway. The Merseyrail and Glasgow commuter rail networks also have below ground stations. Crossrail 2 is a