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
Central line (London Underground) interchange, it was ruled out on grounds of cost, the disruption it would cause to the Central line while being built and because the platforms would be too close to sidings at Liverpool Street and would not be developed until after Crossrail is fully operational. The developers of the "First Central" business park at Park Royal, west London, were planning a new station between North Acton and Hanger Lane. This would have served the business park and provided a walking distance interchange with Park Royal station on the Piccadilly line. This is not being actively pursued; London Underground has said