London Underground Northern Line

London Underground Northern Line is a Transport for London operated tube line in London, England. Running between Morden and Edgware, Mill Hill East or High Barnet via Bank or Charing Cross, it is coloured black on the tube map. It runs essentially from south-west to north London, with two branches through central London and three in the north. Its southern section runs from Morden in the borough of Merton to Kennington in Southwark, where it then divides into two central branches, one via Charing Cross in the West End and the other via Bank in the City. The central branches re-join at Camden Town, where the line again divides into two branches, one to High Barnet and the other to Edgware in the borough of Barnet. On the High Barnet branch there is a short single-track branch to Mill Hill East only.

For most of its length it is a deep-level tube line. The portion between Stockwell and Borough opened in 1890 and is the oldest section of deep-level tube line on the Underground network. There were about 252 million passenger journeys recorded in 2011/12 on the Northern line, making it the second-busiest on the Underground. (It was the busiest from 2003 to 2010.) It is unique in having two different routes through central London. Despite its name, it does not serve the northern-most stations on the network, though it does serve the southern-most station, Morden, as well as 16 of the system's 29 stations south of the River Thames. There are 50 stations in total on the line, of which 36 have platforms below ground.

History
The implemented service from High Barnet branch gave good access both to the West End and the City. This appears to have undermined traffic on the Alexandra Palace branch, still run with steam haulage to Kings Cross via Finsbury Park, as Highgate (low-level) was but a short bus ride away and car traffic was much lighter than it would become later. Consequently, the line from Finsbury Park to Muswell Hill and Alexandra Palace via the surface platforms at Highgate was closed altogether to passenger traffic in 1954.

In 1975, the Northern City Line, known by that time as the Highbury branch, was transferred from London Underground to British Rail; it is now served by Great Northern. In the past, before the introduction of the 1995 stock, the Northern line was sometimes nicknamed the "Misery Line" in the press because of its perceived unreliability.

The line has a complicated history, and the current complex arrangement of two main northern branches, two central branches and the southern route reflects its genesis as three separate railways, combined in the 1920s and 1930s. An extension in the 1920s used a route originally planned by a fourth company. Abandoned plans from the 1920s to extend the line further southwards, and then northwards in the 1930s, would have incorporated parts of the routes of two further companies. From the 1930s to the 1970s, the tracks of a seventh company were also managed as a branch of the Northern line. An extension from Kennington to Battersea is currently under construction, which may either give the Northern line a second southern branch or may see it split into separate distinct lines with their own identities.

In 1938, 1938 Stock trains were introduced.

In 1959, 1959 Tube Stock trains were introduced.

On 26 June 1972, 1972 Mk1 Stock trains were introduced and the 1938 stock trains were withdrawn with also the line being converted into a full 1959 and 1972 Mk1 Stock operation.

On 12 June 1998, brand new 1995 Tube Stock trains were introduced.

In 1999, the 1972 Mk1 Stock was withdrawn.

In 2000, the 1959 Tube Stock was withdrawn and the line was converted into a full 1995 Tube Stock operation.

On 26 February 2013, the first section of the line (West Finchley to High Barnet) was transferred to the new signalling system and converted to ATO.

On 30 May 2013, the 1995 Tube Stock trains went under refurbishment.

On 1 June 2014, the line became fully automated with the Chalk Farm to Edgware via Golders Green section being the last part of the line to switch to ATO.

On 13 April 2015, the entire 1995 Tube Stock fleet was completely refurbished.

Current Route
The Northern Line operates via these primary locations. Charing Cross (West End) branch
 * Morden
 * South Wimbledon
 * Colliers Wood
 * Tooting Broadway
 * Tooting Bec
 * Balham
 * Clapham South
 * Clapham Common
 * Clapham North
 * Stockwell
 * Oval
 * Kennington
 * Kennington (Charing Cross branch)

Bank (City) branch
 * Waterloo
 * Embankment
 * Charing Cross
 * Leicester Square
 * Tottenham Court Road
 * Goodge Street
 * Warren Street
 * Euston (Charing Cross branch)
 * Mornington Crescent
 * Camden Town (High Barnet branch)
 * Kentish Town
 * Tuffnell Park
 * Archway
 * Highgate
 * East Finchley
 * Finchley Central (High Barnet branch)
 * Finchley Central (Mill Hill East branch)
 * West Finchley
 * Woodside Park
 * Totteridge & Whetstone
 * High Barnet
 * Kennington (Bank branch)
 * Elephant & Castle
 * Borough
 * London Bridge
 * Bank
 * Moorgate
 * Old Street
 * Angel
 * King's Cross St Pancras
 * Camden Town (Edgware branch)
 * Chalk Farm
 * Belsize Park
 * Hampstead
 * Golders Green
 * Brent Cross
 * Hendon Central
 * Colindale
 * Burnt Oak
 * Edgware