THE TUBE

THE tube serves 270 stations and has 402 kilometres (250 mi) of track, 52% of which is above ground The network is considered the oldest rapid transit system, incorporating the world's first underground railway, the Metropolitan Railway, which opened in 1863 and is now part of the Circle, Hammersmith & City and Metropolitan lines; and the first line to operate underground electric traction trains, theCity & South London Railway in 1890, now part of the Northern line.

 The network has expanded to 11 lines, and in 2012/13 carried 1.23 billion passengers, making it the 12th busiest transit system.^[

The system's first tunnels were built just below the surface using the cut and cover method, and are large enough to take trains of normal size. Later, smaller circular tunnels – which give rise to its nickname the Tube – were dug through the London Clay at a deeper level. The early lines were marketed as the UNDERGROUND in the early 20th century on maps and signs at central London stations.  The term 'Tube' is nowadays often used both in official publicity and in general usage to embrace the whole Underground system,

As of 2012, 91% of operational expenditure is covered by passenger fares. The Travelcard ticket was introduced in 1983 and Oyster, a contactless ticketing system, in 2003.

The LPTB was a prominent patron of art and design, commissioning many new station buildings, posters and public artworks in a modernist style. The schematic Tube map, designed by Harry Beck in 1931, was voted a national design icon in 2006 

For the first deep-level tube line, the City and South London Railway, two 10 feet 2 inches (3.10 m) diameter circular tunnels were dug between King William Street (close to today's Monument station) and Stockwell, under the roads to avoid the need for agreement with owners of property on the surface. This opened in 1890 with electric locomotives that hauled carriages with small opaque windows, nicknamed padded cells.

 During air raids in 1915. The Metropolitan promoted housing estates near the railway with the "Metro-land" brand and nine housing estates were built near stations on the line. Electrification was extended north from Harrow to Rickmansworth, and branches opened from Rickmansworth to Watford in 1925 and from Wembley Park to Stanmore in 1932.

 The Piccadilly line was extended north to Cockfosters and took over District line branches to Harrow (later Uxbridge) and Hounslow.

During the war many tube stations were used as air-raid shelters. 

The Underground serves 270 stations. Fourteen Underground stations are outside Greater London, of which five (Amersham, Chalfont & Latimer, Chesham, andChorleywood on the Metropolitan line, and Epping on the Central line), are beyond the M25 London Orbital motorway. Of the 32 London boroughs, six (Bexley, Bromley,Croydon, Kingston, Lewisham and Sutton) are not served by the Underground network, while Hackney has Old Street and Manor House only just inside its boundaries.

Name	Map colour[71]	First operated	Type	Length	No. Sta	Current Stock	Future Stock	Trips per annum	Avg. trips per mile
								(×1000) 2011/12 figures[72]
Bakerloo line	Brown	1906	Deep Tube	23.2 km 14.5 mi	25	1972 Stock	N/A	111,136	7,665
Central line	Red	1900[a]	Deep Tube	74 km 46 mi	49	1992 Stock	N/A	260,916	5,672
Circle line	Yellow	1871[b]	Sub surface	27.2 km 17 mi	36	S Stock[75]	N/A	114,609[c]	4,716
District line	Green	1868	Sub surface	64 km 40 mi	60	D78 Stock S Stock[75]	S Stock	208,317	5,208
Hammersmith & City line	Pink	1864[d]	Sub surface	25.5 km 15.9 mi	29	S Stock[75]	N/A	114,609[c]	4,716
Jubilee line	Silver	1979	Deep Tube	36.2 km 22.5 mi	27	1996 Stock	N/A	213,554	9,491
Metropolitan line	Purple	1863	Sub surface	66.7 km 41.5 mi	34	S Stock	N/A	66,779	1,609
Northern line	Black	1890[e]	Deep Tube	58 km 36 mi	50	1995 Stock	N/A	252,310	7,009
Piccadilly line	Dark Blue	1906	Deep Tube	71 km 44.3 mi	53	1973 Stock	N/A	210,169	4,744
Victoria line	Light Blue	1968	Deep Tube	21 km 13.3 mi	16	2009 Stock	N/A	199,988	15,093
Waterloo & City line	Turquoise	1898[f]	Deep Tube	2.5 km 1.5 mi	2	1992 Stock	N/A	15,892	10,595

1913 Underground poster by Tony Sarg

• The Circle line around Aldgate plays an important role in the Sherlock Holmes story The Adventure of the Bruce-Partington Plans (published in the anthology His Last Bow)