Ealing Broadway interlocking machine room

Ealing Broadway IMR
WP
Overview
Opened	30 November 1952
Operator	London Underground

Ealing Broadway (prefix WP) is an Interlocking Machine Room (IMR) and former signal cabin close to the station of the same name on London Undergrounds District and Central lines. It is destined to become one of the last operational examples of a miniature lever frame in the UK outlasting the Four Lines Modernisation (4LM) re-signalling programme which completes in 2023.  

District Railway

The first of the three railways through Ealing Broadway opened on 6 April 1838 as part of Isambard Kingdom Brunel’s Great Western Railway (GWR) between Taplow and London Paddington. Ealing station did not open until December of that year being renamed to Ealing Broadway in 1875.

District Railway (DR) services commenced from a separate station at Ealing Broadway on 1 July 1879 as an extension of the Richmond branch diverging at Turnham Green. The DR signal cabin (prefix WP) that opened with the line was fitted with a full-size McKenzie & Holland interlocked lever frame of 37 levers. Whilst the DR and GWR stations where distinctly separate, a track connection between the two facilitated a short-lived DR service to operate between Mansion House, Ealing Broadway, and Windsor (now Windsor & Eton Central) between 1883 and 1885. The Windsor service was a commercial failure with the compact rigid wheeled rolling stock of the DR being grossly inadequate for such extended journey times when compared with the GWR. As a result, further DR plans to run to Uxbridge Vine Street where never developed. Electrification of the DR had been ongoing since 1903 with the first electric trains reaching Ealing Broadway in 1905. The original DR station building was rebuilt into the surviving structure that can be seen at street level today.

Central London Railway

Central London Railway (CLR) services commenced from Ealing Broadway on 3 August 1920 as part of a joint venture (known as the Ealing & Shepard’s Bush Railway) with the GWR to link the Great Western Mainline to the Shepard’s Bush goods complex and West London Railway. In return, CLR services could be extended from Wood Lane to Ealing Broadway. As a result, the two-track terminus at Ealing Broadway for the CLR was built to GWR designs features of which can still be seen today. The CLR platforms were controlled from a dedicated lever frame (prefix L) which was co-located in the existing DR signal cabin such where the space constraints on this site.

Despite the DR and CLR having both been merged into Underground Electric Railways of London (UERL) by 1920, the DR continued to retain a separate station and ticket hall from the CLR which in turn was accessed from the GWR station.

London Transport

UERL along with the Metropolitan Railway was merged into the unified entity of London Underground as part of London Passenger Transport Board under the brand of London Transport (LT) in 1933. For the Underground, this resulted in the mass standardisation of operating practises ranging from station signage and publicity to rolling stock and signalling. Whilst many of these ambitions where heavily delayed by the outbreak of WW2, the presentation of a unified transportation network remains one of the enduring legacies of the London Transport era.

On 30 November 1952, the final signal cabin opened at Ealing Broadway replacing the 1879 DR signal cabin and the CLR lever frame. Being a comparatively late LT signal cabin, it was equipped with a Westinghouse push button desk dispensing with earlier hand worked power frames which had dominated many of the post-war signal cabins equipped by Westinghouse on London Underground. Signallers would set up routes via push buttons which would then be enacted by a series of electrically interlocked relays and carried out by the lever frame of the interlocking machine room (IMR) powered by compressed air. In the event of a failure, the air supply to the IMR lever frame could be isolated and worked manually in the case of Ealing Broadway resembling the operation of an N-style power frame.

The implementation of push button working would come to represent one of the final evolutionary phases of signal cabins on London Underground. Push button desks along with the development of automated programme machines in the 1960’s would enable control of entire lines to be concentrated into a single facility doing away with de-centralised signal cabins. Ealing Broadway was subsequently demoted to IMR status after 11 May 1974 with Earl’s Court Control Room assuming control of the District line and remote supervision of the Central line passing to White City signal cabin (prefix CG).

Automatic Train Operation

Central line

Re-signalling of the Central line with Automatic Train Operation (ATO) meant that Ealing Broadway (Central) gained a Signalling Equipment Room (SER) in the early 1990’s located next to the IMR and former signal cabin. The link between the District and Central lines had been severed some time before in advance of re-signalling from 17 May 1993 with control initially passing to a panel located in White City signal cabin. Wood Lane control room would not assume control until 6 July 1999 such were the complexities of integrated this line with its numerous signal cabins into a single facility.

District line

For the District line, it was the introduction of the S7 stocks between 2013 and 2015 that was to prove the catalyst for wholesale re-signalling of the Sub-Surface Railway. Bombardier, manufacturers of the S stock train, were also contracted to replace legacy fixed-block signalling with Distance To Go Radio (DTGR), a form of Automatic Train Operation (ATO). The re-signalling was to be known as the Sub-Surface Upgrade Programme (SSUG). However, Bombardier’s inexperience in delivering signalling systems soon started to drag the SSUG behind schedule and faced with mounting costs and delays, London Underground terminated the contract in 2013 at an estimated cost of £900m and a completion date delay of five years.

Thales won the re-tendered contract for SSR re-signalling in 2015 which had been renamed as Four Lines Modernisation (4LM). Thales would introduce Communications Base Train Control (CBTC), a variant of SelTrac ATO. Migration to ATO on the SSR is split into 14 Signal Migration Areas (SMA) of which Ealing Broadway IMR lies in SMA 11 concerning the railway between Chiswick Park and Ealing Broadway. In advance of 4LM re-signalling, control of the District line between Barons Court and Ealing Broadway was transferred to South Kensington control room as part of the Piccadilly Interim Control Upgrade (PICU) which migrated areas of control away from Earl’s Court control room as well as dispensing use of the pioneering programme machines which were considered unreliable, technologically obsolete and life expired.

However, owing to financial pressures within Transport for London (TFL) exacerbated by the Covid-19 pandemic, SMA 11 was de-scoped from 4LM. Future plans including the Piccadilly line taking over the Ealing Broadway branch and eventual re-signalling to ATO remain ambitions but as of 2021 remain unfunded. As a result, Ealing Broadway IMR is destined to become one of the last authentic working examples of a miniature lever frame in the world after completion of the remainder of 4LM by 2023 with the sole other example being Maidstone East signal box operated by Network Rail in Kent.