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 Underground infrastructure were originally maple wood, then aluminium from 1963, and this had been replaced with plastic or rubber following an increase in serious injuries following falls. However, following the King's Cross fire, aluminium treads have been used. There are 426 escalators on the London Underground system and the longest, at , is at Angel. The shortest, at Stratford, gives a vertical rise of . There are 184 lifts across the Underground, with 72 stations having step-free access from street to train. Major efforts have taken place to improve accessibility across the Underground, with the Jubilee line extension having lifts from opening