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
History of the London Underground early years of the 20th century, UD signs appeared outside stations in central London. World War I delayed extensions of the Bakerloo and Central London Railways, and people used the tube stations as shelters during air raids in 1915. After the war, government-backed financial guarantees were used to expand the network, and the tunnels of the City and South London and Charing Cross, Euston and Hampstead Railways were linked at Euston and Kennington, although the combined service was not named the Northern line until later. The Piccadilly line was extended north to Cockfosters and took over District line branches to