The London Underground system comprises intro 11 lines, including Bakerloo, Central, Circle, Metropolitan, Northern, District, Hammersmith & City, Jubilee, Piccadilly, Waterloo & City, Victoria that serve overall 270 stations, which are operated by the Transport for London, coded as TfL. The Underground serves around 270 stations, from which 16 Underground stations are accessible outside the London region: 8 can be reached on the Metropolitan line and other eight on the Central line. Five out of these stations serve Amersham, Chalfont, Latimer, Chorleywood, and Chesham on the Metropolitan line, while Epping serves on the Central line; Those stations are beyond the 'M25 London Orbital' motorway. The rest 32 stations serve London boroughs; 6 stations serve Bexley, Croydon, Bromley, Kingston, Sutton, and Lewisham; However, these six stations are not provided by the Underground network, while the Hackney has Old Street, right on the Northern line Bank branch, and Manor House, available on the Piccadilly Line, is open only inside of its boundaries. Lewisham was served via the East London Line, which had stations at New Cross and New Cross Gate. However, later the station and its line were transferred to the London Overground network in the 2010s. The Busiest London Underground Stations King's Cross St. Pancras was ranked as the busiest station on the network in 2017, which was used by 97 million passengers, while Roding Valley was the least used station, with only 368,413 passengers. The total number of annu
London Underground consists of 11 lines, with a total of 402 kilometers (250 mi) in length, which makes the Underground being the fourth-longest metro system worldwide. Underground lines are made up of the deep-tube lines and the sub-surface network lines. Around 55% of the line system runs on the surface. London Underground has 93 miles (150 km) of the tube tunnel and about 20 miles (32 km) of the cut-and-cover tunnel. The Underground lines are electrified with a four-rail DC system. A conductor rail among the rails is energized at -210 V; Another rail outside the running tracks is excited at +420 V, which gives a difference of about 630 V in general. The average speed on the Underground reaches 20.5 mph (33.0 km/h); While the outside tunnels of central London run at over 40 mph (64 km/h), mostly in the countryside and suburban areas. The Metropolitan line of London can reach the maximum speeds of 62 mph (100 km/h). Sub-surface Network Lines The Circle, Metropolitan, District, and Hammersmith & City lines are part of the sub-surface network. These lines have a circular bi-directional loop around zone 1. The Circle Line and the Hammersmith & City share stations, the most of their track, along with the district and the Metropolitan lines. The Circle Line is designated with Yellow color and is 27.2 km (17.0 mi) length. The line serves 36 stations, has seven cars, and depending on the statistics of 2017, it reached an average of 257,391-weekday ridership. The District Line is marked with Green color. It is around 64.