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.^[1] 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.^[2][3]

Liverpool Street Interlocking Machine Room

The table below is an alphabetical listing of the extant Interlocking Machine Rooms on the London Underground network in August 2024.^[4]

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^[5] 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^[6] but had been decommissioned by August 2024.^[7][8][9][4]

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

See also

Interlocking

Liverpool Street signal box