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
Seoul Subway Line 5 underground railway tunnels of any kind constructed. Today it is the third longest continuous underground subway tunnel in the world, just behind Guangzhou Metro Line 3 and Beijing Subway Line 10. The line was built 1990~1996 and is an important east-west link connecting Gimpo Airport, the Yeouido business area, downtown Seoul, and the Gangdong residential districts. In 1996 Line 5 was implemented with Automatic train operation. However, it was deemed that a driver would be necessary in case of a breakdown of the automation system, therefore each subway train has one driver on board. It was the world's longest underground