# Interlocking machine room

An Interlocking machine room (IMR) is a component of the London Underground signalling system. Interlocking is an arrangement of signal apparatus that prevents conflicting movements through an arrangement of tracks such as junctions or crossings. On the London Underground signals and points are operated and controlled by an array of electrical, pneumatic and mechanical components. IMRs are unmanned and generally located adjacent to points or at platform ends, and provide a secure and weatherproof enclosure for pneumatically controlled mechanically and electrically interlocked levers mounted horizontally in an upright lever-frame or with a converted manual lever frame.
The table below is an alphabetical listing of the extant Interlocking Machine Rooms on the London Underground network in August 2024.
London Underground operational Interlocking machine rooms :
| IMR Code | IMR name / location | LU Line | Location | Multiple codes controlled |
| BB | Queen's Park Depot | Bakerloo | | |
| BD | Paddington | Bakerloo | in middle of platform | |
| BM | Baker Street | Bakerloo | | |
| BP | Piccadilly Circus | Bakerloo | | |
| BR BS | Waterloo | Bakerloo | | |
| JB | Harrow-on-the-Hill North Subsidiary | Metropolitan | | |
| JB | Harrow-on-the-Hill South Subsidiary | Metropolitan | | |
| JF | Northwood | Metropolitan | | |
| JJ | Watford South Junction | Metropolitan | | |
| L | King's Cross | Piccadilly | | |
| MM | Neasden Depot | Metropolitan Jubilee | | |
| JB | Harrow-on-the-Hill | Metropolitan | within manned cabin | JB subsidiaries and JF |
| JP | Watford | Metropolitan | | |
| JP | Rickmansworth | Metropolitan | within manned cabin | JP, JJ |
| JT | Chalfont & Latimer | Metropolitan | | |
| JW | Amersham | Metropolitan | within manned cabin | JW, JT |
| MD | Finchley Road | Metropolitan | | was MD JB |
| MG JG | Wembley Park | Metropolitan | | |
| MP | Rayners Lane | Metropolitan Piccadilly | With manned Cabin | MU, MW |
| MU | Ruislip Siding | Metropolitan Piccadilly | | |
| MW | Uxbridge Sidings | Metropolitan Piccadilly | | |
| PB | Green Park | Piccadilly | at end of platform | |
| PD | Holborn | Piccadilly | | |
| PG | Wood Green | Piccadilly | at end of platform | |
| PJ | Arnos Grove | Piccadilly | | |
| PK | Oakwood | Piccadilly | inside former cabin | |
| PM | Cockfosters | Piccadilly | inside former cabin | |
| WD | Hammersmith | District Piccadilly | | |
| WF | Parsons Green East | District | | |
| WF | Parsons Green West | District | | |
| WG | Putney Bridge | District | | |
| WK | Waterloo | Waterloo and City | inside former cabin | |
| WK | Turnham Green | District Piccadilly | | |
| WL | Acton Town (East) | District | | |
| WL | Acton Town (West) | District | | |
| WM | Ealing Common | District | | |
| WM | Hanger Lane junction | District | | |
| WP | Ealing Broadway | District | inside former cabin | |
| WR | Northfields Depot | Piccadilly | | |
| WS | Boston Manor | Piccadilly | | |
| WT | Hounslow Central | Piccadilly | | |
| WV | South Harrow | Piccadilly | | |
| WW | Hatton Cross | Piccadilly | at end of platform | |
| WY | Heathrow Terminals 2 and 3 | Piccadilly | at end of platform | |
| WZ | Heathrow Terminal 5 | Piccadilly | | |
As London Underground train control is modernised and updated some Interlocking Machine Rooms are made redundant. The table below is an alphabetical listing of the IMRs on the London Underground network that were operational in 1994 but had been decommissioned by August 2024.
London Underground decommissioned Interlocking machine rooms :
| IMR Code | IMR name / location | LU Line | Location | Multiple codes controlled | Decommissioned |
| AC | Colindale | Northern | at end of platform | | 2008-19 |
| AE | Edgware | Northern | inside former cabin | | 2008-19 |
| B | Kennington | Northern | | | 2008-19 |
| B | Shoreditch | East London | | | 2002-08 |
| C | Charing Cross | Northern | inside former cabin | | 2008-19 |
| CG | White City | Central | within manned cabin | EAB, NOA | 1994-2002 |
| E | Camden Town (Platform 1) | Northern | | | 2008-19 |
| E | Camden Town (Platform 4) | Northern | | | 2008-19 |
| EAB | Ealing Broadway | Central | | | 1994-2002 |
| ET | Canal Junction (south of Surrey Quays) | East London | within manned cabin | | 1994-2002 |
| ET | New Cross Gate | East London | | | 1994-2002 |
| F | Hampstead | Northern | inside former cabin | | 2008-19 |
| FB | Bromley-by-Bow | District | | | |
| FC | Plaistow | District | | | |
| FE | East Ham | District | | | |
| FF | Barking | District | within manned cabin | FB – FG | |
| FF | Barking Sidings West | District | | | |
| FF | Barking Sidings East | District | | | |
| FG | Dagenham East | District | | | |
| FJ | Hornchurch | District | | | |
| FM | Upminster | District | within manned cabin | FJ – FM | |
| FM | Upminster West | District | | | |
| G | Golders Green South | Northern | | | 2008-19 |
| G | Golders Green North | Northern | | | 2008-19 |
| HON | Holborn | Central | | | 1994-2002 |
| JE | Willesden Green | Metropolitan Jubilee | | | |
| JL | Stanmore Sidings | Jubilee | | | 2008-19 |
| JP | Rickmansworth | Metropolitan | within manned cabin | JP, JJ | |
| LB | Liverpool Street | Central | in manned cabin in middle of platform | | 1994-2002 |
| LC | Bethnal Green | Central | in manned cabin in middle of platform | | 1994-2002 |
| LF | Leytonstone | Central | in manned cabin | | 1994-2002 |
| LJ | Woodford | Central | in manned cabin | | 1994-2002 |
| LL | Hainault | Central | in manned cabin | Also controlled LL Grange Hill subsidiary area | 1994-2002 |
| LP | Newbury Park | Central | in manned cabin | | 1994-2002 |
| LT | Loughton | Central | in manned cabin | | 1994-2002 |
| LU | Debden | Central | in manned cabin | | 1994-2002 |
| LW | Epping | Central | in manned cabin | LW, LX | 1994-2002 |
| LX | North Weald | Central | in former manned cabin | | 1994-2002 |
| M | Moorgate | Northern | inside former cabin | | 2008-19 |
| MAA | Marble Arch | Central | | | 1994-2002 |
| NN | Archway | Northern | inside former cabin | | 2008-19 |
| NOA | North Acton | Central | | | 1994-2002 |
| NOR | Northolt | Central | at end of platform | | 1994-2002 |
| NP | East Finchley | Northern | inside former cabin | | 2008-19 |
| NQ | Finchley Central | Northern | inside former cabin | | 2008-19 |
| NU | High Barnet | Northern | inside former cabin | | 2008-19 |
| OP | Edgware Road | Metropolitan | within manned cabin | | 2008-19 |
| OZ | Hammersmith | Metropolitan | within manned cabin | | 2008-19 |
| QUE | Queensway | Central | at end of platform | | 1994-2002 |
| RUG | Ruislip Gardens | Central | | | 1994-2002 |
| TF | Green Park | Jubilee | | | 2008-19 |
| TG | Charing Cross | Jubilee | at end of platform | | 2008-19 |
| U | Stockwell | Northern | | | 2008-19 |
| VE | Brixton | Victoria | at end of platform | | 2008-19 |
| VF | Victoria | Victoria | at end of platform | | 2008-19 |
| VG | Warren Street | Victoria | at end of platform | | 2008-19 |
| VH | King's Cross St Pancras | Victoria | at end of platform | | 2008-19 |
| VJ | Highbury & Islington | Victoria | | | 2008-19 |
| VK | Finsbury Park | Victoria | | | |
| VL | Seven Sisters | Victoria | | | 2008-19 |
| VN | Northumberland Park Depot | Victoria | | | 2008-19 |
| VP | Walthamstow Central | Victoria | at end of platform | | 2008-19 |
| W | Tooting Broadway | Northern | at end of platform | | 2008-19 |
| WER | West Ruislip | Central | within manned cabin | WER, RUG, NOR | 1994-2002 |
| WB | West Kensington East | District Piccadilly | inside former cabin | | |
| WC | West Kensington West | District Piccadilly | | | |
| X | Angel | Northern | in former manned cabin at end of platform | | 1994-2002 |
| Y | Morden | Northern | | | 2008-19 |
| EN | Whitechapel | District | within manned cabin | | 2021 |
| EC | Earl's Court | District | at end of platform | | 2022 |
| ED | High Street Kensington | District | | | 2022 |
| ED | Triangle Sidings (Kensington) | District | | | 2022 |
| EE | Gloucester Road | District | | | 2022 |
| EF | South Kensington | District | | | 2022 |
| EG | Mansion House | District | | | 2021 |
| EH | Embankment | District | at street level | | 2021 |
| EJ | Tower Hill | District | in middle of platform | | 2021 |
| MB | Baker Street | Metropolitan | under platforms 1 & 2 | | 2019 |
| ML | Swiss Cottage | Metropolitan | | | 2019 |
| OB | Aldgate | District Metropolitan | | | 2021 |
| OD | Liverpool Street | Metropolitan | inside former cabin | | 2021 |
| OE | Moogate | Metropolitan | | | 2021 |
| OH | Farringdon | Metropolitan | | | 2021 |
| OJ | King's Cross St Pancras | Metropolitan | at end of platform | | 2021 |
| L | King's Cross | Northern | inside former cabin | | |
| J | Euston | Northern | | | |