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
Attacks on the London Underground in London. On 7 July 2005, bombs exploded on Underground trains between Aldgate and Liverpool Street stations, Russell Square and King's Cross St. Pancras stations and Edgware Road and Paddington stations. A double-decker bus at Tavistock Square was also destroyed. The bombs were detonated by four homegrown terrorist suicide bombers. The explosions killed 52 people and resulted in over 700 injuries. Four more attacks, unconnected with those on 7 July, were attempted on 21 July 2005 at Shepherd's Bush Market, Warren Street and Oval stations, as well as on a bus in Bethnal Green. In these incidents, each bomb detonator