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
London Overground than a solid single line, to distinguish it from the colour-coded Underground lines. The London Overground also uses a variant of the TfL roundel. TfL denotes its different transport modes such as London Underground or London Buses with variants of the roundel device using a range of colours, and the London Overground version consists of an orange ring with a blue bar. The roundel has its origins in a 1933 design by the London Passenger Transport Board and has spawned many variations. Unlike other National Rail stations, London Overground stations which are not served by another National Rail operator now