User:Goldenarrw/Four Lines Modernisation

Four Lines Modernisation (shortened to 4LM) is a wholesale re-signalling programme encompassing London Underground’s Circle, District, Hammersmith & City and Metropolitan lines. Combined, these lines make up over 40% of the network and cover the oldest sections of urban rapid transit in the world dating back to 1863.

Origins
The Circle, District, Hammersmith & City and Metropolitan lines, known as the sub-surface lines, have a complex intertwined history stretching from the heart of the City of London to rural backwaters with many historical oddities ranging from timetables to rolling stock and infrastructure. The introduction of the S7 and S8 stock constructed by Bombardier between 2009 and 2017 was the first successful attempt since the 1950’s to introduce a standardized design of rolling stock for these closely interlinked lines all of which share significant portions of their route with one another with numerous flat junctions posing a significant obstacle to increasing service frequency even with new trains.

Following on from this, in 2011, London Underground awarded Bombardier Transportation the contract for a signalling upgrade programme initially called Sub-Surface Upgrade Programme (SSUP) with the aim of providing the sub-surface lines with Automatic Train Control (ATC) to increase capacity making the best use of the 192 fleet of new trains, at the time the largest single rolling stock order for a train operator in the United Kingdom.

However, by December 2013, it was becoming apparent that Bombardier’s inexperience in this field was making delivery of the project increasingly fraught and London Underground subsequently terminated the contract through an £85 million break off settlement. The collapse of this programme prompted an uproar at the time leading to a highly critical report published by London Assembly citing inherent weaknesses in the procurement process. The culmination of this saga led to Thales being selected as the replacement for the now renamed Four Lines Modernisation in the Summer of 2015 with a revised final completion date of 2023, five years later than originally planned.

Scope
Whilst centralised control centres first pioneered by London Transport in the 1960’s on the Victoria line had attempted to concentrate signal control into larger areas, large portions of these lines are still controlled by signal cabins covering small geographic areas through push button or mechanical lever frames requiring manual input from signallers as well as regular maintenance for equipment that is now obsolete and increasingly expensive to maintain and repair. As an example of this, Edgware Road signal cabin of 1926 vintage, required over 3600 manual lever movements a day to move trains through an area encompassing just two stations.

Prior to the commencement of 4LM, the sub-surface lines had existing control centres at Baker Street and Earl’s Court as well as signal cabins at Amersham, Barking, Edgware Road, Hammersmith, Harrow-on-the-Hill, Rayners Lane, Rickmansworth, Whitechapel and Upminster. All existing London Underground operated control centres and signal cabins will be progressively closed and transfer to Hammersmith Service Control Centre.

The sub-surface lines have been split into Signal Migration Areas (SMA’s) numbered 0.5 to 14 by which a variant of Automatic Train Control (ATC) referred to by Thales as Communications Based Train Control (CBTC) will replace fixed block signalling dispensing with most lineside signals in the process.

Conventional colour light signalling will be retained over the following sections where non-compatible rolling stock shares track with the sub-surface lines:

Harrow-on-the-Hill – Moor Park (Main Lines only): Metropolitan line shared with Chiltern Railways on London Underground infrastructure but using Network Rail-style fixed block signalling

Gunnersbury – Richmond: District line shared with London Overground operating over Network Rail infrastructure

Acton Town – Ealing Common: District line shared with the Piccadilly line using legacy fixed block signalling

East Putney – Wimbledon: District line shared with South Western Railway using Network Rail controlled signalling infrastructure

Progression
On 17 March 2019, SMA 0.5 was pressed into revenue earning service closing Hammersmith OZ signal cabin which at the time of closure was over 60 years old. This marked the beginning of the rolling programme of signal migration across the sub-surface lines aimed at reducing risk and disruption through weekend closures by compartmentalising parts of the railway to be worked on.

On 1 September 2019, both SMA 1 and SMA 2 were brought into use closing the then 93-year-old Edgware Road OP signal cabin reputed to be the oldest signal cabin still in use on a rapid transit system anywhere in the world. This was also the first time that CBTC was being used by all four sub-surface lines.

The rollout of SMA 2 in particular over the Metropolitan line between Finchley Road and Euston Square was the subject of intense scrutiny over the high rate of cancellations caused by the repeated pushing back of the roll out date requiring a significant pool of drivers to undertake refresher courses for working with CBTC operated trains.

In the wake of the Coronavirus pandemic and subsequent lockdown ordered by the UK Government, in March 2020 all work on Transport for London construction sites and upgrade projects including 4LM were brought to a safe stop. It was announced at the end of June 2020 that works would resume as restrictions eased.

Following a review of Transport for London's finciacies triggered by an emergency bailout package from the UK Government, several projects including those affecting London Underground where placed into review. In August 2020, the scope of Four Lines Modernisation was reduced when SMA's 10, 11 and 12 were removed from the programme. The affected areas on the District line west of Baron's Court and south of Fulham Broadway will retain existing fixed block signalling equipment.

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