THE SIGNAL BOX

OVERSEAS

KINGSBRIDGE
Great Southern & Western Railway

by John Hinson

Kingsbridge signal cabin
Photograph by Dr. J W F Scrimgeour 5/71

Kingsbridge signal cabin controlled the Great Southern & Western Railway's Dublin terminus of that name. In 1966, the station was renamed Heuston and the nameplate affixed to the box reflects this.

The conventional-looking timber construction gives no clue that this is not a mechanical signal cabin but a power installation, opened n the 9th October, 1938. A multi-head, multiple aspect signal can be seen in this view, as can a multiple aspect ground signal. The roof of the box isn't quite flat, as might appear, but has a very shallow hipped arrangement.

This view, from the direction of the terminus, looks towards Inchicore and Cork. A through route passes behind the box and through Phoenix Park tunnel to connect with West Road on the Midland Great Western.

Power lever frame inside Kingsbridge box
Photograph by Dr. J W F Scrimgeour 5/71

Stepping inside the cabin, we find an interesting lever frame of 76 levers controlling the layout. Three power frames of this type were built locally by the Great Southern Railway at their Broadstone workshops (for here, West Road and Westland Row) and take the term "miniature lever frame" literally! Levers are 18" long and spaced at 4" intervals. All of the functions of the frame are electric, but the interlocking is mechanically by tappets like a conventional frame.

This type of frame was introduced in the 1930s, as an economy measure over the importation of "true" power frames.

Installation of this frame at Kingsbridge allowed the box to also control the areas of two other boxes - Islandbridge Junction (which was where the West Road line diverged on the approaches to the station) and Liffey Bridge Junction (lower left on the diagram, on the West Road line).

Seven years after the cabin and station were renamed Heuston, the diagram in the box still showed the old name of Kingsbridge but this has since been altered. In this view, some spare (white) levers are evident, but alterations have utilised all of these and there are now ten additional switches operating signals (mostly added 1972-3) for which there is no space in the frame.

Zerograph instrument at Kingsbridge
Photograph 19/12/63, collection of Dr J W F Scrimgeour

There are three running lines between Islandbridge Junction and Inchicore. The two main lines were, at the time of these pictures, worked by Harper's instruments whilst the Up Goods (or "Third Line") was signalled using this intriguing instrument known as a Zerograph.

The origins of the instruments is not known, but they were in use by 1880. The G&SW Rule Book describes their use:

In order to bring the Pointer on the dial of the instrument in Islandbridge Junction Cabin so as to notify the destination of trains going onto the Third Line, the signalman at Inchicore must give the required number of beats on the Right Hand Key corresponding with the number shown over the printed destination on the Dial-plate, which must be repeated by the Signalman in Islandbridge junction Cabin in order to show the signal is received and understood.

A signal given in error can be cancelled by seven beats with the Right Hand Key.

Immediately the signalman in Islandbridge Junction Cabin has acknowledged the Signal given on Dial, both cabins must bring the Pointers to Zero by pressing down the Left Hand Key, so that then instruments may be available for taking on another train without delay.

It is intriguing to note that the plate at the top of the instrument is marked "Kingsbridge" which is, of course, the name of the box it is installed in as opposed to the more normal labelling showing which box an instrument works to.

Every lever of the 76-lever frame in Heuston signal cabin was in use until relatively recently, but many became spare during 2002 when part of the layout under its control was resignalled. The box closed in late 2002.

The unusual miniature lever frame has been taken out and it is intended to put it on permanent display behind glass at Heuston Station.

Compiled from notes by Dr. J W F Scrimgeour, Tony Gray and Simon Lowe

About the photographs



Comments about this article should be addressed to John Hinson