View source for Northern City Line

{{Short description|Partly underground railway line in London}}
{{distinguish|text=the [[Northern line]] or the [[North London line]]}}
{{redirect|Moorgate Line|the line formerly running into Moorgate via Farringdon|City Widened Lines}}
{{Use dmy dates|date=October 2025}}
{{Use British English|date=October 2025}}
{{Infobox rail line
| box_width                       = auto
| name                            = Northern City Line
| color                           = 
| logo                            = 
| logo_width                      = 
| image                           = Class 717 at Moorgate.jpg
| image_width                     = 300px
| caption                         = A [[British Rail Class 717|Class 717]] at [[Moorgate station|Moorgate]]
| type                            = [[Commuter rail]], [[Suburban rail]]
| system                          = [[National Rail]]
| status                          = Operational
| locale                          = [[Greater London]]
| start                           = [[Finsbury Park station|Finsbury Park]]
| end                             = [[Moorgate station|London Moorgate]]
| stations                        = 6
| routes                          = 
| daily_ridership                 = 
| open                            = 1904
| close                           = 
| owner                           = [[Network Rail]]
| operator                        = [[Thameslink and Great Northern|Great Northern]]
| character                       = 
| depot                           = [[Hornsey EMU depot and former steam locomotive shed|Hornsey]]
| stock                           = [[British Rail Class 717|Class 717 "Desiro City"]]
| linelength                      = 
| tracklength                     = 
| tracks                          = Two
| gauge                           = {{RailGauge|sg|allk=on}}
| load_gauge                      = [[Loading gauge#Great Britain|W6]]<ref>[http://www.networkrail.co.uk/browse%20documents/rus%20documents/route%20utilisation%20strategies/east%20coast%20main%20line/east%20coast%20main%20line%20rus.pdf Network Rail: RUS, ECML Page 57] {{Webarchive|url=https://web.archive.org/web/20080529152115/http://www.networkrail.co.uk/browse%20documents/rus%20documents/route%20utilisation%20strategies/east%20coast%20main%20line/east%20coast%20main%20line%20rus.pdf |date=29 May 2008 }} Accessed 19 February 2011</ref>
| electrification                 = {{plainlist|
* [[25 kV AC|25 kV 50 Hz AC]] [[OHLE]] (north of Drayton Park)
* 750 [[Volt|V]] [[Direct current|DC]] [[third rail]] (south of Drayton Park)
}}
| speed                           = 
| elevation                       =
| map                             = [[File:Northern City Line.png|300px]]
| map_state                       = uncollapsed
}}
{{Northern City Line|collapse=y}}
The '''Northern City Line''' (NCL) is a [[commuter rail]]way line in England, which runs from [[Moorgate station]] to [[Finsbury Park station|Finsbury Park]] in [[London]] with services running beyond. It is part of the [[Great Northern Route]] services, and operates as the south-eastern branch of the [[East Coast Main Line]] (ECML). It is underground from Moorgate to [[Drayton Park railway station|Drayton Park]] in Highbury, from which point it runs in a cutting until joining the ECML south of Finsbury Park. Its stations span northern inner districts of [[Greater London]] southwards to the [[City of London]], the UK's main financial centre. Since December 2015, its service timetable has been extended to run into the late evenings and at weekends,<ref>{{cite web |title=Great Northern timetable changes from 13 December 2015 |url=http://www.thameslinkrailway.com/your-journey/timetables/dec-2015-gn |publisher=Govia Thameslink Railway |access-date=13 December 2015 |archive-url=https://web.archive.org/web/20170311092059/https://www.thameslinkrailway.com/your-journey/timetables/dec-2015-gn |archive-date=11 March 2017 |url-status=dead }}</ref> meeting a new franchise commitment for a minimum of six trains per hour until 23:59 on weekdays and four trains per hour at weekends.<ref>{{cite web |title=East Coast Mainline Routes & Branches part 2 |date=29 September 2013 |url=http://www.londonreconnections.com/2013/east-coast-mainline-routes-branches-part-2-hertford-loop-northern-city-line/ |publisher=London Reconnections |access-date=13 December 2015 |archive-date=22 December 2015 |archive-url=https://web.archive.org/web/20151222131556/http://www.londonreconnections.com/2013/east-coast-mainline-routes-branches-part-2-hertford-loop-northern-city-line/ |url-status=live }}</ref>

The official name for this line is the '''Moorgate Line''',<ref name="Sectional Appendix">{{cite book |author=Network Rail |author-link=Network Rail |title=London North Eastern Route Sectional Appendix |volume=Module LN2 |date=December 2006 |id=LN105 Seq 001 |page=41}}</ref><ref>Quail Map 2 – England East [page 14] February 1998 (Retrieved 10 March 2016)</ref> but it is rarely referred to as this due to confusion with the [[Widened Lines]] route from {{rws|Kentish Town}} to {{rws|Farringdon}}, which, until March 2009, also served {{rws|Moorgate}} surface-level station on the [[London Midland Region of British Railways|London Midland Region]].<ref>{{cite book |author=Network Rail |author-link=Network Rail |title=Kent Sussex & Wessex Sectional Appendix |volume=Module KSW2 |date=December 2009 |id=SO280 Seq 001 |page=136}}</ref><ref>Quail Map 4 – Midlands & North West [page 1R] June 2015 (Retrieved 10 March 2016)</ref> The Northern City Line's name is derived from the fact that it was originally a [[London Underground]] line, where it was described or managed as part of both the [[Metropolitan line|Metropolitan]] and [[Northern line|Northern]] lines (sometimes as the "Highbury Branch"), although never connected to either. Built as an isolated route with a northern terminus at Finsbury Park, reconstruction connected it to the [[British Rail]] network in 1976 and began its modern service pattern. One of London's deep-level railways, the Northern City is unlike the others in being owned by [[Network Rail]] and served by commuter trains operated by [[Thameslink and Great Northern|Great Northern]] from Moorgate to Finsbury Park and onwards to [[Hertfordshire]].

== History{{anchor|Great Northern and City Railway Act 1892|Great Northern and City Railway Act 1895|Great Northern and City Railway Act 1897|Great Northern and City Railway Act 1902|Great Northern and City Railway Act 1903|Great Northern and City Railway Act 1904|Great Northern and City Railway Act 1907|Metropolitan Railway Act 1913}} ==
{{Infobox UK legislation
| short_title           = Great Northern and City Railway Act 1892
| type                  = Act
| parliament            = Parliament of the United Kingdom
| long_title            = An Act for incorporating the Great Northern and City Railway Company and empowering them to construct a railway from the Canonbury branch of the Great Northern Railway near Finsbury Park to the city of London and for other purposes.
| year                  = 1892
| citation              = [[55 & 56 Vict.]] c. ccxlii
| introduced_commons    = 
| introduced_lords      = 
| territorial_extent    = 
| royal_assent          = 28 June 1892
| commencement          = 
| expiry_date           = 
| repeal_date           = 
| amends                = 
| replaces              = 
| amendments            = 
| repealing_legislation = 
| related_legislation   = 
| status                = 
| legislation_history   = 
| theyworkforyou        = 
| millbankhansard       = 
| original_text         = 
| revised_text          = 
| use_new_UK-LEG        = 
| UK-LEG_title          = 
| collapsed             = yes
}}
{{Infobox UK legislation
| short_title           = Great Northern and City Railway Act 1895
| type                  = Act
| parliament            = Parliament of the United Kingdom
| long_title            = An Act to extend the powers for the purchase of Lands and the time for the completion of the Great Northern and City Railway.
| year                  = 1895
| citation              = [[58 & 59 Vict.]] c. cxii
| introduced_commons    = 
| introduced_lords      = 
| territorial_extent    = 
| royal_assent          = 6 July 1895
| commencement          = 
| expiry_date           = 
| repeal_date           = 
| amends                = 
| replaces              = 
| amendments            = 
| repealing_legislation = 
| related_legislation   = 
| status                = 
| legislation_history   = 
| theyworkforyou        = 
| millbankhansard       = 
| original_text         = https://www.legislation.gov.uk/ukla/Vict/58-59/112/pdfs/ukla_18950112_en.pdf
| revised_text          = 
| use_new_UK-LEG        = 
| UK-LEG_title          = 
| collapsed             = yes
}}
{{Infobox UK legislation
| short_title           = Great Northern and City Railway Act 1897
| type                  = Act
| parliament            = Parliament of the United Kingdom
| long_title            = An Act to extend the powers for the purchase of land and the time for the completion of the Railway authorised by the Great Northern and City Railway Act 1892 and to amend some of the provisions of that Act.
| year                  = 1897
| citation              = [[60 & 61 Vict.]] c. cxciii
| introduced_commons    = 
| introduced_lords      = 
| territorial_extent    = 
| royal_assent          = 6 August 1897
| commencement          = 
| expiry_date           = 
| repeal_date           = 
| amends                = 
| replaces              = 
| amendments            = 
| repealing_legislation = 
| related_legislation   = 
| status                = 
| legislation_history   = 
| theyworkforyou        = 
| millbankhansard       = 
| original_text         = https://www.legislation.gov.uk/ukla/Vict/60-61/193/pdfs/ukla_18970193_en.pdf
| revised_text          = 
| use_new_UK-LEG        = 
| UK-LEG_title          = 
| collapsed             = yes
}}
{{Infobox UK legislation
| short_title           = Great Northern and City Railway Act 1902
| type                  = Act
| parliament            = Parliament of the United Kingdom
| long_title            = An Act to confer further powers on the Great Northern and City Railway Company and to extend the time for the completion of the authorised railway of that Company and for other purposes.
| year                  = 1902
| citation              = [[2 Edw. 7]]. c. ccxxii
| introduced_commons    = 
| introduced_lords      = 
| territorial_extent    = 
| royal_assent          = 8 August 1902
| commencement          = 
| expiry_date           = 
| repeal_date           = 
| amends                = 
| replaces              = 
| amendments            = 
| repealing_legislation = 
| related_legislation   = 
| status                = 
| legislation_history   = 
| theyworkforyou        = 
| millbankhansard       = 
| original_text         = 
| revised_text          = 
| use_new_UK-LEG        = 
| UK-LEG_title          = 
| collapsed             = yes
}}
{{Infobox UK legislation
| short_title           = Great Northern and City Railway Act 1903
| type                  = Act
| parliament            = Parliament of the United Kingdom
| long_title            = An Act to amend the Great Northern and City Railway Act 1902 and to authorise the Great Northern and City Railway Company to raise additional capital for the purposes of their undertaking.
| year                  = 1903
| citation              = [[3 Edw. 7]]. c. v
| introduced_commons    = 
| introduced_lords      = 
| territorial_extent    = 
| royal_assent          = 30 June 1903
| commencement          = 
| expiry_date           = 
| repeal_date           = 
| amends                = 
| replaces              = 
| amendments            = 
| repealing_legislation = 
| related_legislation   = 
| status                = 
| legislation_history   = 
| theyworkforyou        = 
| millbankhansard       = 
| original_text         = https://www.legislation.gov.uk/ukla/Edw7/3/5/pdfs/ukla_19030005_en.pdf
| revised_text          = 
| use_new_UK-LEG        = 
| UK-LEG_title          = 
| collapsed             = yes
}}
{{Infobox UK legislation
| short_title           = Great Northern and City Railway Act 1904
| type                  = Act
| parliament            = Parliament of the United Kingdom
| long_title            = An Act to extend the time for the completion of railways and for other purposes.
| year                  = 1904
| citation              = [[4 Edw. 7]]. c. viii
| introduced_commons    = 
| introduced_lords      = 
| territorial_extent    = 
| royal_assent          = 24 June 1904
| commencement          = 
| expiry_date           = 
| repeal_date           = 
| amends                = 
| replaces              = 
| amendments            = 
| repealing_legislation = 
| related_legislation   = 
| status                = 
| legislation_history   = 
| theyworkforyou        = 
| millbankhansard       = 
| original_text         = https://www.legislation.gov.uk/ukla/Edw7/4/8/pdfs/ukla_19040008_en.pdf
| revised_text          = 
| use_new_UK-LEG        = 
| UK-LEG_title          = 
| collapsed             = yes
}}
{{Infobox UK legislation
| short_title           = Great Northern and City Railway Act 1907
| type                  = Act
| parliament            = Parliament of the United Kingdom
| long_title            = An Act to revive and extend the powers for the purchase of lands and to extend the time limited for the completion of the railway and works authorised by the Great Northern and City Railway Act 1902 and for other purposes.
| year                  = 1907
| citation              = [[7 Edw. 7]]. c. lxxvi
| introduced_commons    = 
| introduced_lords      = 
| territorial_extent    = 
| royal_assent          = 28 July 1907
| commencement          = 
| expiry_date           = 
| repeal_date           = 
| amends                = 
| replaces              = 
| amendments            = 
| repealing_legislation = 
| related_legislation   = 
| status                = 
| legislation_history   = 
| theyworkforyou        = 
| millbankhansard       = 
| original_text         = https://www.legislation.gov.uk/ukla/Edw7/7/76/pdfs/ukla_19070076_en.pdf
| revised_text          = 
| use_new_UK-LEG        = 
| UK-LEG_title          = 
| collapsed             = yes
}}
{{Infobox UK legislation
| short_title           = Metropolitan Railway Act 1913
| type                  = Act
| parliament            = Parliament of the United Kingdom
| long_title            = An Act to transfer to and vest in the Metropolitan Railway Company the undertaking of the Great Northern and City Railway Company to empower the Metropolitan Railway Company to construct a new railway and works to acquire additional land to raise additional capital and for other purposes.
| year                  = 1913
| citation              = [[3 & 4 Geo. 5]]. c. liv
| introduced_commons    = 
| introduced_lords      = 
| territorial_extent    = 
| royal_assent          = 15 August 1913
| commencement          = 
| expiry_date           = 
| repeal_date           = 
| amends                = 
| replaces              = 
| amendments            = 
| repealing_legislation = 
| related_legislation   = 
| status                = 
| legislation_history   = 
| theyworkforyou        = 
| millbankhansard       = 
| original_text         = https://www.legislation.gov.uk/ukla/1913/54/contents
| revised_text          = 
| use_new_UK-LEG        = 
| UK-LEG_title          = 
| collapsed             = yes
}}
The '''Great Northern & City Railway''' (GN&CR) was planned to allow electrified trains to run from the [[Great Northern Railway (Great Britain)|Great Northern Railway]] (GNR, now the [[East Coast Main Line]]) at [[Finsbury Park station|Finsbury Park]] to the [[City of London]] at [[Moorgate station|Moorgate]]. Despite being built using similar methods to the tube network then under construction, the tunnels were built large enough to take a main-line train, with an internal diameter of {{convert|16|ft|m}}, compared with those of the [[Central London Railway]] with a diameter less than {{convert|12|ft|m}}. For this reason the line was popularly known as the "Big Tube" in its early days.<ref>{{cite book|title=Underground, Overground: A Passenger's History of the Tube|last=Martin|first=Andrew|date=2012|publisher=Profile|isbn=9781846684784|location=London|chapter=Chapter 6: Three more tubes}}</ref> However, the GNR eventually opposed the scheme and cancelled its electrification plans, and the line opened in 1904 with the northern terminus in tunnels underneath Finsbury Park GNR station. It was originally electrified using an unusual fourth-rail system with a [[Third rail|conductor rail]] outside each running rail.<ref name=CULG/>

The GN&CR was bought in 1913 by the [[Metropolitan Railway]] (MR), which operated what are today the [[Metropolitan line|Metropolitan]] and [[Hammersmith & City line]]s and the former [[East London line]]. The MR had plans to link it to the [[Circle line (London Underground)|Circle]] and [[Waterloo & City line|Waterloo & City]] lines, but these were never fulfilled.<ref name=CULG>{{cite web|url=http://www.davros.org/rail/culg/northern.html|access-date=9 March 2012|work=Clive's UndergrounD Line Guides|title=Northern line|date=3 March 2012|archive-date=11 February 2015|archive-url=https://web.archive.org/web/20150211152300/http://www.davros.org/rail/culg/northern.html|url-status=live}}</ref> During this period, the line remained an isolated branch, without through services to any other part of the rail network. Carriages were brought to it through a connection into a freight yard near Drayton Park station, where a small depot was built to service trains.

The GN&CR generating station closed when the MR took over, and became the studio of [[Gainsborough Pictures]]. After lying derelict for many years, it became a temporary venue for the [[Almeida Theatre]]. The site has since been redeveloped as apartments.

After the formation of the [[London Passenger Transport Board]] in 1933, the MR was amalgamated with the other Underground railways and the line was renamed the Northern City Line. In 1934 it was re-branded as part of the Edgware–Morden line (which was renamed the Northern line in 1937), and in 1939 operations were transferred from the Metropolitan to the Northern. As part of London Transport's [[New Works Programme]], the [[Northern Heights plan]] was to connect the Northern City Line at Finsbury Park to existing main-line suburban branches running to [[Alexandra Palace]], [[High Barnet]] and [[Edgware]], which would be taken over by London Transport and electrified. The Highgate branch of the Edgware–Morden line would connect to this network north of Highgate. Only parts of this plan were completed: when the [[World War II|Second World War]] started, the Highgate link and electrification of the Barnet branch were well under way and ultimately completed, but the Northern City connection to Highgate was first postponed and finally cancelled after the war.
[[File:Northern Heights small.png|thumb|The planned 1930s [[Northern line#Northern Heights plan|Northern Heights extensions]], showing the diversion of the Northern City Line to Alexandra Palace, Bushey Heath and High Barnet. Sections marked in solid green were ultimately taken over. The line from Highgate to Finsbury Park already existed but was to be absorbed by London Transport; this never happened and it closed to passengers in 1954. After being used to transfer tube trains from Highgate depot to the Northern City line, it closed permanently in 1970.]]
After the war there were proposals to extend the Northern City Line north and south. The London Plan Working Party Report of 1949 proposed several new lines and suburban electrification schemes for London, lettered from A to M. The lower-priority routes J and K would have seen the Northern City Line extended to [[Woolwich]] (Route J) and [[Crystal Palace, London|Crystal Palace]] (Route K), retaining the "Northern Heights" extensions to Edgware and Alexandra Palace. The lines would have run in small-diameter tube tunnels south from Moorgate to Bank and [[London Bridge station|London Bridge]].<ref>J. Glover, "London's Underground", 7th edition, Shepperton, Ian Allan, 1991, p.61.</ref> The "K" branch would have run under [[Peckham]] to [[Peckham Rye railway station|Peckham Rye]], joining the old [[Crystal Palace (High Level) railway station|Crystal Palace (High Level)]] branch (which was still open in 1949) near Lordship Lane. Nothing came of these proposals, and the Edgware, Alexandra Palace and Crystal Palace (High Level) branches were all closed to passengers in 1954. As a result, the Northern City Line remained isolated from the rest of the network.

In 1964, the Northern City Line (low level) platforms at Finsbury Park were given over to become the southbound platforms of both the Piccadilly line and the new Victoria Line, the former [[Piccadilly line]] platforms becoming the northbound Piccadilly and Victoria lines' platforms. From this time the NCL used Drayton Park as its terminus. At the same time a change was made at [[Highbury & Islington station|Highbury & Islington]], with the northbound Northern City line diverted to a new platform alongside the northbound Victoria line, and the southbound Victoria using the former northbound Northern City platform, both providing [[cross-platform interchange]]. Passengers from Moorgate to Finsbury Park took the Northern City line to Highbury & Islington and then changed onto the Victoria Line.

In 1970 the line was connected (as intended by its original promoters) to the mainline via the high level platforms at Finsbury Park as part of a wider plan to electrify ECML suburban services. The line was renamed '''Northern line (Highbury Branch)''' and the following year an agreement was made to transfer it to [[British Rail]]. Commuter trains were run to/from Moorgate instead of [[London King's Cross railway station|King's Cross]], relieving congestion at King's Cross.

The last London Underground services ran in October 1975 and British Rail services commenced in August 1976, replacing services to [[Broad Street railway station (London)|Broad Street]] via the [[North London Line City Branch|city branch]] of the [[North London Line]]. These British Rail services used the name "[[Great Northern Route|Great Northern Electrics]]". The track and tunnels are now owned by Network Rail. Services are provided by [[Thameslink and Great Northern|Great Northern]] to {{stnlnk|Welwyn Garden City}} and, via the [[Hertford Loop Line]], to {{stnlnk|Hertford North}} (with some extending to [[Stevenage railway station|Stevenage]], [[Hitchin railway station|Hitchin]] or [[Letchworth Garden City railway station|Letchworth]]). The name "Northern City Line" has been revived to refer to the underground part of the route.

==Infrastructure==
From Finsbury Park to Drayton Park traction current is supplied at 25 [[volt|kV]] [[Alternating current|AC]] via [[OHLE|overhead line]], controlled by York Electrical Control Room.<ref name="NCL DC Lines">{{cite book|title=Work Instructions for D.C. Electrified Lines on the Northern City Line|publisher=Network Rail|location=London, UK|date=June 2007}}</ref>

[[File:Essex Road stn signage2.JPG|thumb|Network SouthEast branding at Essex Road station.]]
From Drayton Park to Moorgate traction current is supplied at 750 V [[Direct current|DC]] via [[third rail]]. There are two electrical sections,<ref name="NCL DC Lines"/> separated by a gap at Poole Street:
* Queensland Road to Poole Street
* Poole Street to Finsbury Circus

Trains change from AC to DC traction supply, or vice versa, whilst standing at Drayton Park station.<ref name="NCL DC Lines"/> The platform starting signal on the Up platform at Drayton Park is held at danger (red) as the train approaches. This ensures that all trains stop to lower the pantograph before going into the tunnel.

In the 1970s the original London Underground fourth-rail traction current supply was converted to a third-rail 750V DC system. The redundant centre fourth-rail was disconnected and left in situ since it was difficult to remove in the narrow tunnels.<ref>{{Cite magazine |last=Stephen |first=Paul |date=4 May 2022 |title=Signal of intent: a key milestone in the switch to digital |magazine=Rail |volume=956 |page=22 }}</ref>

Signalling is controlled from Kings Cross panel at York ROC.<ref name="NCL DC Lines"/> Between Drayton Park and Moorgate, there is no [[Automatic Warning System]] or [[Train Protection & Warning System]] equipment provided, due to the position of the auxiliary return rail.<ref name="NCL DC Lines"/> All signals are multiple aspect colour light signals fitted with [[train stop]] arms.<ref name="NCL DC Lines"/>

=== East Coast Digital Programme ===
Works to commission new [[European Train Control System|ETCS]] digital signalling on the line, along with the first test train under the new system, took place during the Early May Bank Holiday in 2022.<ref>{{Cite web | url=https://www.networkrailmediacentre.co.uk/news/northern-city-line-enters-new-phase-as-east-coast-digital-programme-prepares-to-commission-new-equipment | title=Northern City Line enters new phase as East Coast Digital Programme prepares to commission new equipment | access-date=30 April 2022 | archive-date=30 April 2022 | archive-url=https://web.archive.org/web/20220430081534/https://www.networkrailmediacentre.co.uk/news/northern-city-line-enters-new-phase-as-east-coast-digital-programme-prepares-to-commission-new-equipment | url-status=live }}</ref> The new signalling system was approved by the [[Office of Rail and Road]] in March 2023, and gradually introduced on passenger services from 27 November 2023.<ref>{{Cite web |date=27 November 2023 |title=Commuters look forward to more reliable services as first passenger trains run to City of London using digital signalling |url=https://www.mynewsdesk.com/uk/govia-thameslink-railway/pressreleases/commuters-look-forward-to-more-reliable-services-as-first-passenger-trains-run-to-city-of-london-using-digital-signalling-3289065 |access-date=16 December 2023 |website=Mynewsdesk |language=en}}</ref> By November 2024, all passenger services were operated under ETCS signalling,<ref>{{Cite web |date=13 November 2024 |title=All City of London route trains are now digitally signalled |url=https://www.railadvent.co.uk/2024/11/all-city-of-london-route-trains-are-now-digitally-signalled.html |access-date=4 December 2024 |website=RailAdvent}}</ref> with traditional lineside signals completely removed on 18 May 2025.<ref>{{cite web |title=History is made as First Commuter Railway in the UK goes Signal-Free |url=https://www.railadvent.co.uk/2025/05/history-is-made-as-first-commuter-railway-in-the-uk-goes-signal-free.html |website=RailAdvent |access-date=19 May 2025 |date=24 May 2025}}</ref>

==Operational procedures==
[[File:NCL Procedures Sign 01.jpg|thumb|right|NCL Start of Procedures sign & Up platform starting signal at Drayton Park]]Because mainline trains operate over the infrastructure inherited from London Underground, there are some practices on the NCL which differ from Railway Rulebook instructions, and these are contained in an additional publication.<ref name="NCL DC Lines"/> These include:

===Passing signals at danger===
{{update-section|date=November 2025}}
If a train is standing at a signal at danger ''inside a tunnel'' and it is not possible for the driver to contact the signaller, the driver is permitted to [[Signal passed at danger#with authority|pass that signal under their own authority]]. As soon as the train starts to move, the tripcock on the train will automatically operate and bring the train to a stop, so the driver must reset it before continuing. They must then proceed with caution, be prepared to stop short of any obstruction, and not travel any faster than {{Convert|3|mph|abbr=on}}.<ref name="NCL DC Lines"/> When they reach the next signal they must stop and attempt to contact the signaller, to inform the signaller of what has taken place regardless of the aspect that it is showing.

Platform starting signals, which let the train ''into'' a tunnel, can only be passed at danger with the signaller's authority.<ref name="NCL DC Lines"/>

===Assisting a failed train===
Unlike surface lines, the driver of a train which fails on the NCL is not required to leave the train to lay [[Detonator (railway)|detonators]] and then wait for the assisting train. The driver remains with the train and the signaller will authorise the driver of the assisting train to proceed to the rear of the failed train at a maximum speed of {{Convert|3|mph|abbr=on}}.<ref name="NCL DC Lines"/> To ensure that the rear of the failed train is always visible, all trains working over the NCL are required to display three red lights at their rear: two tail lamps plus the red portion of the destination roller blind.<ref name="NCL DC Lines"/>

On reaching the failed train, the assisting driver will stop short then clip their tunnel telephone onto the tunnel wires so that they can discuss with the driver of the failed train how to carry out the assistance in order to get the trains moving again. Then the two trains are coupled together and the drivers can talk to each other over the usual cab-to-cab handsets before proceeding.

==Rolling stock==
[[File:Welwyn Garden City Train, Moorgate 8 May 2013.jpg|thumb|Class 313 unit at Moorgate]]
As part of its contract to supply electrical equipment during the construction of the line, in 1901 [[British Thomson-Houston]] provided 35 sets of traction control equipment to [[Brush Electrical Engineering Company]] and [[Dick, Kerr & Company]]. The original plan was for 11 seven-car trains (33 motors and 44 trailers) and one [[shunting locomotive]]. Initially 26 motorcars and 32 trailer cars were built. They were known as the 'wooden' cars because they were fabricated of teak and mahogany on steel underframes. In 1906 Brush delivered another five motors and 13 trailers. There were of all-steel construction and naturally-enough referred to as 'steel cars'. The GN&CR converted one trailer to a motor car, bringing the fleet to 32 motors and 44 trailers. (The remaining sets of traction control equipment were used as maintenance spares.) Normal operation was six-car formations at peak times, reduced to two-car sets at other times. Cars were {{convert|56|ft|6|in|abbr=on}} long over buffers, {{convert|9|ft|4|in|abbr=on}} wide, and {{convert|12|ft|2|in|abbr=on}} in height. Seats were provided for 58 passengers in the wooden trailers and 64 in the steel ones. Motor cars seated 54 because of a {{convert|2|ft|10|in|cm|abbr=on}} equipment compartment behind the driver's cab. Uniquely in England, coupling between cars was by means of [[link and pin]] on the centre-line.<ref name="The Big Tube">{{cite book |last=Bruce |first=J. Graeme |date=1976 |title=The Big Tube: A short illustrated history of London's Great Northern & City Railway |location=London |publisher=London Transport |pages=27–32 |isbn=0853290717 }}</ref>

The original fleet of 76 carriages was withdrawn and replaced by [[London Underground Standard Stock]] on 15 May 1939.<ref name="The Big Tube" /> These became the last pre-1938 trains running on the Underground, being phased out during the last weeks of October 1966 through 3 November. [[London Underground 1938 Stock|1938 tube stock]] serviced the line, in variously three-, four- and six-car formations, until its temporary closure on 4 October 1975.<ref>{{cite book |last=Connor |first=Piers |date=1989 |title=The 1938 Tube Stock |location=Harrow Weald, Middlesex, England |publisher=Capital Transport |pages=85–86 |isbn=1854141155 }}</ref>

Services are currently operated by dual-voltage [[British Rail Class 717|Class 717]] [[electric multiple unit]]s (EMUs), which replaced [[British Rail Class 313|Class 313]] units as part of a franchise commitment when [[Govia Thameslink Railway]] took over management of the line and its services.<ref name="guardian">{{cite news |last=Topham |first=Gwyn |title=FirstGroup loses Thameslink franchise to Go-Ahead joint venture |url=https://www.theguardian.com/business/2014/may/23/firstgroup-loses-thameslink-franchise-go-ahead-joint-venture |access-date=24 May 2014 |newspaper=The Guardian |location=London |date=23 May 2014 |archive-date=23 May 2014 |archive-url=https://web.archive.org/web/20140523214358/http://www.theguardian.com/business/2014/may/23/firstgroup-loses-thameslink-franchise-go-ahead-joint-venture |url-status=live }}</ref> The Class 717s began to enter service in March 2019.<ref name=fullserviceentry>{{cite web |url=https://www.railmagazine.com/news/network/great-northern-class-717s-finally-enter-passenger-service |title=Great Northern Class 717s finally enter passenger service |access-date=27 March 2019 |archive-date=27 March 2019 |archive-url=https://web.archive.org/web/20190327091508/https://www.railmagazine.com/news/network/great-northern-class-717s-finally-enter-passenger-service |url-status=live }}</ref> To comply with regulations for trains operating in single-bore tunnels where there is not enough clearance space for side evacuation, they have emergency doors at both ends of a unit. When operating on {{nowrap|750 V DC}}, the two motor coaches of a Class 313 collected traction current from their own shoe gear only; there was no traction bus linking them together as found on most electric multiple units. All of the Class 313 units when operating on the NCL had their Driving Motor B vehicle at the London end, and whilst on {{nowrap|750 V DC}} were electronically limited to {{convert|30|mph|abbr=on}},<ref>First Capital Connect: Class 313 Conversion Training Guide p.9 General Information "75 mph maximum speed AC Mode– Automatically regulated to 30mph when in DC Mode" 2009.</ref> which is the maximum line speed.<ref name="Sectional Appendix"/> All stations are long enough to accept six-car trains.<ref>[[Network Rail]], Rules Of The Plan, 2009, London North Eastern Region</ref>

==Accidents and incidents==

===Moorgate tube crash===

{{Main|Moorgate tube crash}}

The Moorgate tube crash, which killed 43 people, is the most serious peacetime accident on the London Underground. It occurred at [[Moorgate station]] on 28 February 1975, when a Highbury Branch train ran through the terminus at speed and crashed into the dead end of the tunnel beyond. The crash was found to have been caused by the driver, who was killed, but the specific cause was never determined; a report found that there was insufficient evidence to say whether it was a deliberate act of the driver or due to a medical condition.

===Tunnel penetration incident===
On 8 March 2013, [[Pile driver|pile boring]] operations on a building site in East Road, Hackney, {{Convert|13|m|abbr=on}} above the tunnel, penetrated and obstructed the line between Old Street and Essex Road stations. A serious accident was averted by the actions of an observant train driver, and the line was restricted for several days for repairs. A subsequent investigation by the [[Rail Accident Investigation Branch]] was highly critical of carelessness on the construction companies involved and the planning approval process.<ref>{{Cite web |title=Report 03/2014: Penetration of a tunnel at Old Street |url=https://www.gov.uk/raib-reports/penetration-and-obstruction-of-a-tunnel-between-old-street-and-essex-road-stations-london |access-date=20 May 2025 |website=GOV.UK |language=en}}</ref>

==Passenger volume==
This is the number of passengers using stations on the line from the year beginning April 2002 to the year beginning April 2019. These numbers include all passengers using the station, not just Northern City Line users.{{GBsta-u|
{{GBsta-u A|stn=Finsbury Park|u1=3,006,865|u2=5,021,634|u3=5,041,828|u4=5,875,109|u5=5,545,881|u6=5,492,164|u7=6,566,019|u8=7,337,297|u9=6,448,792|u10=6,430,270|u11=6,429,584|u12=6,263,994|u13=5,656,786|u14=7,032,726|u15=6,781,272|u16=7,614,996|u17=7,669,706|u18=2,013,500|u19=4,600,424|u20=8,559,032}}
{{GBsta-u A|stn=Drayton Park|u1=164,459|u2=129,849|u3=118,426|u4=288,324|u5=279,243|u6=261,164|u7=338,246|u8=478,144|u9=505,230|u10=552,840|u11=572,418|u12=625,436|u13=690,750|u14=791,700|u15=859,130|u16=860,124|u17=784,628|u18=174,134|u19=358,386|u20=516,734}}
{{GBsta-u A|stn=Highbury and Islington|u1={{n/a|No data}}|u2={{n/a|No data}}|u3={{n/a|No data}}|u4=4,809,098|u5=4,751,391|u6=4,173,338|u7=5,668,133|u8=7,625,235|u9=11,800,800|u10=14,695,098|u11=15,840,018|u12=19,975,522|u13=28,166,440|u14=29,852,702|u15=29,507,772|u16=30,439,574|u17=29,398,624|u18=8,660,736|u19=17,186,284|u20=20,601,096}}
{{GBsta-u A|stn=Essex Road|u1=356,425|u2=118,145|u3=115,680|u4=274,645|u5=384,504|u6=336,338|u7=401,718|u8=474,340|u9=482,764|u10=521,464|u11=572,332|u12=627,430|u13=715,984|u14=810,518|u15=861,234|u16=856,598|u17=768,438|u18=197,416|u19=407,786|u20=556,966}}
{{GBsta-u A|stn=Old Street|u1={{n/a|No data}}|u2={{n/a|No data}}|u3={{n/a|No data}}|u4=733,612|u5=813,166|u6=827,762|u7=1,326,797|u8=1,434,785|u9=1,336,722|u10=1,396,260|u11=1,455,920|u12=1,682,134|u13=3,611,484|u14=5,323,546|u15=5,756,246|u16=7,119,730|u17=6,768,052|u18=2,230,872|u19=3,672,524|u20=5,437,172}}
{{GBsta-u A|stn=London Moorgate|u1=832|u2=7,135,238|u3=7,263,068|u4=9,235,925|u5=10,108,616|u6=9,373,435|u7=6,736,698|u8=7,187,012|u9=7,860,382|u10=7,997,460|u11=9,051,956|u12=9,397,890|u13=8,849,564|u14=10,833,978|u15=10,433,502|u16=11,508,936|u17=9,993,570|u18=1,934,826|u19=3,346,156|u20=5,587,716}}
}}

== Future ==
On 13 October 2025, [[Transport for London]] submitted a business case to the [[Department for Transport]] for full ownership of the Northern City Line.<ref>{{Cite web |last=Stubbings |first=David |title=TfL submits business case to take over Northern City Line to Moorgate |url=https://www.railmagazine.com/news/tfl-submits-business-case-to-take-over-northern-city-line-to-moorgate |access-date=23 October 2025 |publisher=Rail Magazine|url-access=registration |language=en}}</ref><ref>{{Cite web |title=Tfl submits business case to dft for transfer of northern city line services - 15 Oct 2025 - Rail Magazine - Readly |url=https://gb.readly.com/magazines/rail/2025-10-15/68e8b61cd09f8f758e549781 |access-date=23 October 2025 |website=gb.readly.com |url-access=subscription|language=en}}</ref>

==See also==
* [[Northern Heights plan]]

== References ==
{{reflist|30em}}

===Bibliography===
{{refbegin}}
* {{cite book|last= Bruce|first= J. Graeme|title= The Big Tube: A short illustrated history of London's Great Northern & City Railway|location= London|publisher= [[London Transport Executive (GLC)|London Transport]]|date= 1976|isbn= 0-85329-071-7}}
{{refend}}

== External links ==
{{commons category}}

{{Great Northern Route}}
{{Railway lines in London}}
{{Northern line navbox}}
{{Metropolitan line navbox}}

[[Category:Transport in the City of London]]
[[Category:Transport in the London Borough of Islington]]
[[Category:Railway lines in London]]
[[Category:Railway lines opened in 1904]]
[[Category:Standard gauge railways in London]]
[[Category:Electric railways in the United Kingdom]]
[[Category:Underground commuter rail]]
[[Category:Northern City Line]]