LU signal box codes

Each signal on London Underground has a number. This number splits into two parts: the signal box or control code, and the actual number. The latter is usually a simple number or is a number suffixed with a letter. There is little consistency in numbering except that:

• sometimes a running signal and associated shunting signal will have the same number with A and B suffixes (in either order);
• on plain line suffixed numbers usually occur in a sequence, so that A10A, A10B, A10C will be in that order;
• a number ending 0 or 00 is usually a draw-up signal in rear of a signal with the related number (so that P120 might be in rear of P12).

Where a signal is controlled by a signal box or remote interlocking, the first part of the number is the code for that signal box. These codes are listed in the main part of this document.

For automatic signals the first part of the number is a control code. Usually this is A, but it is S on some parts of the Northern Line. If drivers are required to treat the signal as if it were controlled, the code will either be a signal box code followed by an X (these signals are in rear of a controlled area, preventing an approaching train from locking the controlled signals), or it is PNX if the signal is protecting temporary work (the code replaces the A for the duration of the work).

Finally, some signals have special control arrangements that are not associated with a signal box. Signals guarding floodgates have a three letter code such as FEX; the second letter indicates the line (in this case the East London), except that on the Victoria Line it is simply FX. Other signals that have special control arrangments but normally work automatically have a simple X (for example, some such signals can be set to danger by the Line Controller). Where a signal checks the position of a temporary crossover, the code is changed to TRX for the duration of the work.

Finally, repeater signals have an R prefixing the main number, while fog repeaters have FR. Where co-acting signals are used, they have a CA suffix.

The signal box codes are one or two letters. The first letter indicates a sequence covering the line or area, and the second letter the individual box in the sequence:

In general this page does not indicate which boxes are still open, but tries to record all codes used in the past. Italics indicate an unconfirmed code.

Tube lines

Bakerloo Line

Locations north of Queen's Park are controlled by Railtrack Willesden Surburban (WS) signal box.

Central Line

Until the 1940s boxes CA to CG were simply A to G.

Ealing Broadway is controlled by the District Line.

The Central Line now uses three letter codes identifying individual interlockings. These codes still need to be added to this page.

Jubilee Line

Baker Street is controlled by the Bakerloo Line. Locations north of there are classified as part of the subsurface lines.

Northern Line

Piccadilly Line

Locations from Baron's Court westwards are classified as part of the subsurface lines. Finsbury Park is controlled by the Victoria Line, and King's Cross St. Pancras by the Northern Line.

Box A was closed in 1932, and the remaining single letter boxes at various times. The P prefix was added to boxes between 1981 and 1984.

Victoria Line

Waterloo & City Line

Subsurface lines

The subsurface lines are not signalled according to the present lines, but rather as they were in the early 20th century.

* In 1985 Jubilee Line signalling was separated from the Metropolitan. ME and MK were renamed, JD, JF, and JG were added, and MH was closed.

Locations on the District line west of Putney Bridge and from Gunnersbury are controlled by Railtrack boxes.

Circle Line/Met codes 1904-1950's A - Praed Street (later Edgware Road) (autos were S) B - Baker Street C - King's Cross D - Farringdon E - Barbican F - Moorgate G - Liverpool Street H - Aldgate

B - Baker Street D - Finchley Road E - Willesden Green F - Neasden G - Wembley Park H - Harrow South J - Harrow Main N - Harrow North P - Rayners Lane T - Eastcote (other source says R) U - Ruislip V - Hillingdon W - Uxbridge

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