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
North London line and London King's Cross stations, so since then this link has only been used for freight trains. It too was singled concurrent with the AC electrification of the eastern part of the North London line. Most of the line runs in a curve across north London. Only and stations at the western end are south of the River Thames. The river crossing is made by Kew Railway Bridge on tracks which are shared with the London Underground District line. The location of the eastern extremity has varied over the years. Between 1944 and 1986, it was at Broad Street station,