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 and Western England. Stations within London are served by two or four trains per hour. The London Overground (often shortened to "Overground") is operated by Arriva Rail London under a concession let by Transport for London, which owns the London Underground. The Overground includes the Watford Local, North & West London, East London & South and the Gospel Oak to Barking lines. It is the only National Rail service shown on the London Underground map. All stations are served at least every 20 minutes, with stations between and on the East London Line having 16 trains per hour in each