London & North Western & Great Western Joint


Opened: 1903

Closed: —

Location code: W62/07

Severn Bridge Junction signal box
Photograph by John Hinson, 1981

The largest operation mechanical signal box (in terms of levers) in Europe today is Severn bridge Junction - with 180 levers. Only one box in the world beats that size - Spencer Street No1 in Melbourne, Australia.

Severn Bridge Junction opened in 1904, and although on joint property of the London & North Western and Great Western Railways, was of pure LNW design. It was built to their standard design of 1876, and is basically a king-sized version of Edgeley Junction No1 although it features taller window sections to allow the signalmen a better view from such a great height. This feature was adopted in all boxes in the LNW's 1904 design, illustrated at Harrow No2.

Interior of Severn Bridge Junction
Photograph by John Hinson, 1981

This view shows part of the 180-lever LNW Tumbler frame, along with the cluttered instrument shelf. Unusually, the signal box diagram is mounted on the end wall of the box - this allows the signalman to clearly see the occupation of track circuits from any point whilst working the levers.

The instruments themselves are an interesting mix of GW and LNW equipment, installed over the years when the different halves of the partnership have had responsibility. Some of these are illustrated and described below.

Signal box diagram at Severn Bridge Junction
Enlargements: Left side · Right side
Photographs by John Hinson, 1981

The track layout diagram shows the layout at this junction. On the left are the through platforms of Shrewsbury Station, leading though to Crewe Junction box. Lower right is English Bridge Junction, one corner of a triangular junction that had a separate signal box until 1955. Between then and 1967, the next box was Coleham, but since then working has been with Sutton bridge Junction, the junction for the Cambrian Coast line and the now closed Severn Valley branch. The third corner of the triangle is controlled from Abbey Foregate box.

Signalling equipment at Severn Bridge Junction
Photograph by John Hinson, 1981

As previously mentioned, Severn Bridge Junction has a hybrid collection of signalling equipment. The Absolute Block instrument is of the GWR 1947 design, adopted as standard by the Western Region of BR, and its associated bell is on the right.

Between them is a Welwyn Release, a device adopted after a famous accident in 1935 at Welwyn Garden City. It prevents a signalman from giving a second Line Clear without winding the handle (on top) many times to reset it. This effectively gives the signalman time to think about the possibility of his accepting a second train into a section already occupied. Under normal operation, the occupation of track circuits at the exit of the section gives the release.

On the left is a LNW Train Describer, described below.

Fletecher Train Describers at Severn Bridge Junction
Photograph by John Hinson, 1981

The LNW train describers were designed in 1891 by J W Fletcher (Telegraph Superintendent, LNWR, 1879-1903) as that company's home-built replacement for the wooden-cased Tyer & Co devices. Although still working by rotating the pointer with electrical pulses, these instruments were all-electric in operation and did not need winding-up in the same way as the Tyer's clockwork devices.

The upper instrument receives indications from Crewe Junction box. The lower instrument transmits indications to Crewe Junction for trains in the opposite direction. The required indication is achieved by the insertion of the peg on the chain into the hole alongside the appropriate indication. This activates the needle to rotate as far as that position. Once the train has passed, the needle is restored to the normal (Maltese cross) position by withdrawing the peg. In this view, the peg has been pulled out slightly to achieve this, but left in the hole for convenience.

Lever collars - WR-style
Photograph by John Hinson, 1981
Lever badge at Severn Bridge Junction
Photograph by John Hinson, 1981

More evidence of GW and Western Region presence is illustrated here. The GW's preferred style of lever collar is shown on the left - an adaption of their standard type (in a larger diameter) obstructs access to the lever catch (stirrup) but doesn't prevent operation in the same way the the LNW's own type (see Edgeley junction No1) does.

On the right, a standard WR ivorine description and pull plate for lever 163 shows how exceptionally long lists of lever pulls are fitted onto the plate.

GWR centre-pivot signals
Photograph by John Hinson, 1981

Much of the outdoor equipment shows the WR's influence too. This bracket signal governs departure from the Up Main Platform towards Wellington (left) or Craven Arms (right) and is worked by levers 11 and 16. Centre-pivot arms have been used to improve visibility beneath the station awning, but unlike the usual type (see Walnut Tree Junction) the lamp and spectacles have been moved to the left side. The arms themselves would no doubt have been mounted lower on the dolls if there hadn't previously been calling-on arms mounted below them.

Signals at Severn Bridge Junction
Photograph by John Hinson, 1974

The LNW origins were maintained in this signal, which lead from the Up & Down Platform line. Like the signal in the previous illustration (seen in the background) the arms lead respectively to the Wellington (lever 26) or Craven Arms (lever 30) lines. The stout wooden post and supporting brackets are distinctive products of that company. The arms themselves (which are slightly shorter than standard) have been renewed by the WR.

The calling-on arms (27/21) are typical of WR practice, featuring a miniature arm with spectacle to the left of the post and coloured with a horizontal white stripe. When lowered, they would reveal an illuminated letter C (lit by the same lamp). Warning and Shunt Ahead arms would show the equivalent W or S.

Severn Bridge Junction is still in use, although some rationalisation of the signalling and layout has taken place. Although various schemes to modernise the signalling have raised their head from time to time, there are no immediate plans for replacement.

About the photographs

Comments about this article should be addressed to John Hinson

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