Editing Northern line (section)

==={{anchor|The Northern Heights plan}} Northern Heights plan===
[[File:Northern Heights diagram.png|thumb|Line map of the abandoned Northern Heights plan]]
[[File:Northern Line Northern Heights Extension sign.jpg|thumb|Sign displaying the route of the Northern Heights extension]]
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{{redirect|Northern Heights|the neighbourhood in Sudbury, Ontario|Urban neighbourhoods of Sudbury#Donovan/Northern Heights|the condominium/mall in Yellowknife, Northwest Territories|Centre Square Mall}}
{{Broader|Edgware, Highgate and London Railway|topic=the detailed history}}
In June 1935 the LPTB announced the [[New Works Programme]], an ambitious plan to expand the Underground network which included the integration of a complex of existing [[London and North Eastern Railway]] (LNER) lines north of [[Highgate]] through the Northern Heights. These lines, built in the 1860s and 1870s by the [[Edgware, Highgate and London Railway]] (EH&LR) and its successors, ran from Finsbury Park to [[Edgware railway station|Edgware]] via Highgate, with branches to [[Alexandra Palace railway station (Muswell Hill branch)|Alexandra Palace]] and [[High Barnet tube station|High Barnet]]. The line taken over would be extended beyond Edgware to [[Brockley Hill tube station|Brockley Hill]], [[Elstree South tube station|Elstree South]] and [[Bushey Heath tube station|Bushey Heath]] with a new depot at [[Aldenham Works|Aldenham]]. The extension's route was that planned for the unbuilt [[Watford and Edgware Railway]] (W&ER), using rights obtained from the earlier purchase of the W&ER (which had long intended an extension of the EH&LR Edgware route towards [[Watford]]). This also provided the potential for further extension in the future; [[Bushey]]'s town planners reserved space in Bushey village for a future station and Bushey Heath station's design was revised several times to ensure this option would remain available in the future.

The project involved [[Railway electrification in Great Britain|electrification]] of the surface lines (operated by steam trains at the time), the doubling of the original single-line section between [[Finchley Central tube station|Finchley Central]] and the proposed junction with the Edgware branch of the Northern line, and the construction of three new linking sections of track: a connection between Northern City Line and Finsbury Park station on the surface; an extension from Archway to the LNER line near [[East Finchley tube station|East Finchley]] via new deep-level platforms below [[Highgate tube station|Highgate station]]; and a short diversion from just before the LNER's Edgware station to the Underground's station of the same name.

====Intended service levels====
The peak-hour service pattern was to be 21 trains an hour each way on the High Barnet branch north of Camden Town, 14 of them via the Charing Cross branch and seven via the Bank branch. 14 would have continued on beyond Finchley Central, seven each on the High Barnet and Edgware branches. An additional seven trains an hour would have served the High Barnet branch but continued via Highgate High-Level and Finsbury Park to Moorgate, a slightly shorter route to the city. It does not seem to have been intended to run through trains to the ex-Northern City branch from Edgware via Finchley Central. Seven trains an hour would have served the Alexandra Palace branch, to/from Moorgate via Highgate High-Level. In addition to the 14 through trains described the ex-Northern City branch would have had 14 four-car shuttle trains an hour.

====Progress of works====
Work began in the late 1930s and was in progress on all fronts by the outbreak of the [[World War II|Second World War]]. The tunnelling northwards from the original Highgate station (now [[Archway tube station|Archway]]) had been completed, and the service to the rebuilt surface station at [[East Finchley tube station|East Finchley]] started on 3 July 1939 but without the opening of the intermediate (new) Highgate Station at the site of the LNER's station of the same name. Further progress was disrupted by the start of the war; however enough development had been made to complete the electrification of the [[High Barnet tube station|High Barnet]] branch onwards from East Finchley (over which tube services started on 14 April 1940) and the new deep-level [[Highgate tube station|Highgate]] station opened on 19 January 1941. The single track LNER line to Edgware was electrified as far as [[Mill Hill East tube station|Mill Hill East]], including the [[Dollis Brook Viaduct]], opening as a tube service on 18 May 1941 to serve the barracks there thus forming the Northern line as it is today. The new depot at Aldenham had already been built and was used to build [[Handley Page Halifax|Halifax]] bombers. Work on the other elements of the plan was suspended late in 1939.

Work on the extension from Edgware to Bushey Heath including work on a viaduct and a tunnel started in June 1939, but was stopped after war broke out.{{sfn|Beard|2002|pp=90–92}} After the war, the area beyond Edgware was made part of the [[Metropolitan Green Belt]], largely preventing the anticipated residential development in the area, and the potential demand for services from Bushey Heath thus vanished. Passenger numbers also dropped on the then-[[British Rail|BR]]'s Mill Hill and Alexandra Palace branches, so it was useless to electrify them. Available funds were directed towards completing the eastern extension of the [[Central line (London Underground)|Central line]] instead, and the Northern Heights plan was dropped on 9 February 1954. Aldenham depot was converted into an overhaul facility for buses.

The implemented service from High Barnet branch gave good access both to the [[West End of London|West End]] and the [[City of London|City]]. This appears to have undermined traffic on the Alexandra Palace branch, still run with steam haulage to [[King's Cross St Pancras tube station|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.{{citation needed|date=May 2020}} This contrasts with the decision to electrify the Epping-Ongar branch of the Central line, another remnant of the New Works programme, run as a tube-train shuttle from 1957. A local pressure group, the Muswell Hill Metro Group, campaigns to reopen this route as a light-rail service.{{citation needed|date=May 2020}} So far there is no sign of movement on this issue: the route, now the [[Parkland Walk]], is highly valued by walkers and cyclists, and suggestions in the 1990s that it could, in part, become a road were met with fierce opposition.{{citation needed|date=May 2020}} Another pressure group has proposed using the track bed further north, as part of the [[North and West London Light Railway]].{{citation needed|date=May 2020}} The connection between [[Drayton Park railway station|Drayton Park]] and the surface platforms at Finsbury Park was opened in 1976, when the Northern City Line became part of [[British Rail]].