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
TfL Rail and in Essex. That branch comprises the first 14 stations on the Great Eastern Main Line, with interchange at Shenfield for medium- and long-distance services beyond to East Anglia. In May 2018 TfL Rail also took over operation of the Heathrow Connect service between in central London and Heathrow Airport to the west (Heathrow Terminal 4 station being the terminus). That route has nine stations. The service is operated by MTR Corporation under contract to Transport for London (TfL). Between May 2016 and May 2017, TfL Rail carried over 47 million passengers on the Shenfield branch. In June 2013 TfL