Editing Metropolitan line (section)

== Four Lines Modernisation (4LM) ==
{{Main|Four Lines Modernisation}}

It was planned that a new signalling system would be used first on the line north of Baker Street from the end of 2016,<ref name="MR" /> but signalling contractor Bombardier was released from its contract by agreement in December 2013 amid heavy criticism of the procurement process<ref>{{Cite web|date=3 January 2014|title=London Underground and Bombardier abandon Tube signalling contract|url=https://www.railjournal.com/financial/london-underground-and-bombardier-abandon-tube-signalling-contract/|access-date=2 June 2020|website=International Railway Journal }}</ref> and London Underground subsequently awarded the contract for the project to [[Thales Group|Thales]] in August 2015.<ref>{{Cite web|date=13 October 2017|title=London Underground resignalling reaches milestone|url=https://www.railjournal.com/signalling/london-underground-resignalling-reaches-milestone/|access-date=2 June 2020|website=International Railway Journal }}</ref>

With the introduction of S8 Stock, the track, electrical supply, and signalling systems are being upgraded in a programme planned to increase peak-hour capacity on the line by 27 per cent by the end of 2023.<ref name="MR">{{cite news |work=Modern Railways |date=January 2013 |pages=38–41 |title=Sub-surface renewal |last=Abbott |first=James}}</ref><ref name="TfL-upgrade">{{cite web|url=http://www.tfl.gov.uk/assets/downloads/corporate/our-upgrade-plan-london-underground-february-2011.pdf |title=Our Upgrade Plan |publisher=Transport for London |date=February 2011 |access-date=7 December 2012 |url-status=dead |archive-url=https://web.archive.org/web/20120817225410/http://www.tfl.gov.uk/assets/downloads/corporate/our-upgrade-plan-london-underground-february-2011.pdf |archive-date=17 August 2012 }}</ref><ref>{{Cite web |title=Four Lines Modernisation|url=https://www.tfl.gov.uk/travel-information/improvements-and-projects/four-lines-modernisation|access-date=2 June 2020|website=Transport for London }}</ref> A single control room for the sub-surface railway opened at Hammersmith on 6 May 2018, and [[communications-based train control]] (CBTC) provided by Thales will progressively replace 'fixed block' signalling equipment dating back the 1940s.<ref name="MR" /><ref name="MR2">{{cite news |work=Modern Railways |date=January 2013 |pages=42–43 |title=Cityflo 650 to control the SSR |last=Stewart |first=Rob}}</ref> Trackside signals with [[automatic train protection]] (ATP) will remain on the line north of Harrow-on-the-Hill, shared with Chiltern Railways DMUs.<ref name="MR" />

The rollout of CBTC has been split into sections, each known as a signal migration area (SMA).<ref>{{Cite journal|date=October 2020|title=Underground News|journal=London Underground Railway Society|volume=706|pages=572}}</ref>

{| class="wikitable sortable"
|+ Metropolitan line signal migration areas
!data-sort-type="number"|{{Abbr|SMA|Signal migration area}}{{efn-lr|SMAs 0.5, 1, 4–7 and 10–12 concern parts of the District, Circle, and Hammersmith & City lines.}}
!from
!class="unsortable"|to
!status
!data-sort-type="isoDate"|date
|-
|2
|Finchley Road
|Euston Square
|completed
|data-sort-value="2019-09" | September 2019
|-
|3
|Euston Square
|Aldgate
|completed
|data-sort-value="2020-07" | July 2020
|-
|8
|Finchley Road
|Preston Road
|planned
|data-sort-value="2024-12" | mid 2025
|-
|9
|Preston Road
|{{plainlist|
* West Harrow
* Moor Park
}}
|planned
|data-sort-value="2025-01" | under review
|-
|13
|Moor Park
|{{plainlist|
* Watford
* Amersham
* Chesham
}}
|planned
|data-sort-value="2025-02" | under review
|-
|14
|West Harrow
|Uxbridge
|deferred
|data-sort-value="2025-03" | 
|}

{{notelist-lr}}

Work on the SMAs north of Finchley Road were delayed in November 2023 because of the complexity of Neasden Depot (shared with the Jubilee Line) and challenges relating to the inter-operability with [[Chiltern Railways]] which shares tracks with the Metropolitan line in this area.<ref name="FOI-4LM">{{cite web |date=November 2023 |title=FOI Request Detail - 4LM |url=https://tfl.gov.uk/corporate/transparency/freedom-of-information/foi-request-detail?referenceId=FOI-2726-2324 |access-date=20 January 2024 |publisher=Transport for London}}</ref>