Irish Railway Record Society

Irish Rail Signalling - Part One
Oliver Doyle

Early signalling in Ireland was limited and records of it are scarce. By 1870 the Irish railway companies were installing ‘modern’ signalling throughout the country – but not enough had been done to prevent the accident at Hamiltonsbawn, between Armagh and Markethill, on 12 June 1889, when 80 people were killed after a train which had stalled was divided and the rear portion ran back, colliding with a following train. This disaster speeded up legislation to ensure adequate signalling and control was provided for the safe passage of trains. On 30 August the Regulation of Railways Act 1889 (which, of course, applied to both Ireland and Great Britain) was enacted with Section One ordering the railways to:

The Irish railway companies complied with the Act by having mechanical interlockings installed or supplied by the major signalling suppliers of the day, McKenzie & Holland, and Saxby & Farmer, both of Worcester, and the Railway Signal Co., Fazakerley, Liverpool. In the first year of the last century, the signalling would have all been relatively new mechanical interlockings. Block instruments controlled the sections on the double lines, generally referred to as ‘Absolute Block’, while electric train staffs (ETS) or tablets (ETT), ‘staff and ticket’ or ‘one engine in steam’ arrangements controlled the single line sections. Only ETS and ‘one train in section’ remains in use on IE’s single lines on the mechanically signalled lines.

During the Civil War many signal cabins were destroyed – some never to be restored – while others were reconstructed. During the late 1920s and early 1930s power-signalling systems were introduced combining the area of control of a few mechanical cabins, but the first major reduction in mechanical signal cabins came in the early 1960s when many sections were lengthened by the closure of signal cabins. This was achievable by the reduction in the number of trains and the increase in speed, with trains, now using diesel traction, taking a shorter time to pass through a section and fewer trains. In 1973, the first Central Traffic Control (CTC) system took over part of the Cork line. At peak there was an estimated 600 signal cabins in Ireland. Today there are 64 on IE, excluding the two CTC boxes. 

 In the CTC area and in areas where there are electric/computerised signal cabins the method of working between interlockings is by Track Circuit Block (TCB). Electric Train Staffs (ETS) control the single line sections between mechanical interlockings. There are only 12 miles of Double Line Absolute Block control remaining, covering four sections:

Glounthaune is normally switched out making a long section Little Island–Cobh. All the sections are worked by Harper’s Patent Double Line Instruments.

 There is a small mileage of ‘one train in section’ working and a number of special arrangements using tokens mainly on freight spurs. There are only four intermediate block posts, which are not located at passenger stations, Waterford West, Killonan, Killucan, and Knockcroghery.

MECHANICAL SIGNAL CABINS

The mechanical signal cabins, most dating from 1889 to the 1950s, have served the railways well in the 100-plus years of their existence, but changing circumstances have made most of the complex station layouts under their control obsolete. There is also the question of maintaining these ageing structures with a high level of wood used in their construction. They range in size from 66 to 1 lever frames and it has been necessary in recent years to substantially overhaul these frames, particularly the locking. The structures have been modernised in many cases using modern materials such as galvanised steel staircases and PVC windows.  To reduce the risk of fire most of the cast iron stoves – the traditional method of heating these structures – have been converted to oil burning. The signal cabin at Rosslare Harbour, a virtually all-wooden structure dating from 1931, was gutted by fire in minutes in December 1997.

The great layouts at three of the largest remaining mechanical cabins Claremorris (66 levers) Mullingar (65) and Athenry (64) are all planned to be drastically reduced within three years as the layouts are renewed and simplified to match current business requirements and reduce maintenance costs.

Throughout the IE system there are many interesting features designed to meet local safe operating requirements. Also there are a number of historic items still in use such as hand-operated electric generators for working electrically operated semaphore signals and points.

The majority of the mechanical signal cabins in use have Railway Signal Company lever frames, though not all identical. Navan, for example, has a RSCo./GNR(I) type. Levers are coloured according to the device they operate:

A small number of frames have a three-position lever for signals or discs. In the centre position the signals/discs are at Danger. When the lever is pushed it clears a disc or signal for a movement over one route while, when it is pulled, it clears an alternative route. An interesting use of this facility exists at Limerick Check cabin where No. 39 points and No. 42 lever work together to provide four routes. When No. 39 points is normal lever No. 42 pushes to give the route in one direction while it is pulled to clear the opposite direction. When points No. 39 are reversed No. 42 levers clears the routes over it in both directions depending on the lever being pushed or pulled.

SEMAPHORE SIGNALS

There are two basic signal types of semaphore signals in use on passenger lines, distant and stop signals while shunt signals control shunting and some freight movements. All three types have both mechanical and colour light versions.

Distant signals are placed a minimum of 880 yards from the next stop signal but this distance can be considerably greater if the approaching speed limit is high or there is a falling gradient involved.

Mechanical stop signals have red and green aspects and the signal arm is red with a white vertical band and a red reflective red band at the outer end. Where two or more stop signals are located together to control a main and diverging routes the signals for the latter have their  arms at  a  lower level than the  signal  for the main route. The up home signal at Claremorris from the Limerick line has three arms. The main arm in the centre reads to the down loop (No. 2 Platform), while at a lower level, either side, are two arms, the right hand one reading to the up loop (No. 1 Platform) and the left hand arm to No. 3 Platform. The up home signal approaching Limerick Junction North from Limerick has three arms, Nos. 11, 12 & 13. No. 11, the tallest reads to the back line which runs from the Limerick line, through the level crossing to the South cabin with which it is slotted and this arrangement controls the direction of down movements between the two cabins. The centre and lowest arm, No.12,  reads to the ‘Limerick Bay’ behind the main platform while the third signal, No. 13, reads to the main north platform. 

Mechanical shunting discs have enamelled metal faces about 320mm x 320mm formed of a white background over-printed  with a red band. A small number of yellow discs exist. The operating difference between the two types is that train cannot pass a red disc until it displays a proceed aspect whereas a driver may pass a yellow disc at either position. This facility is useful where shunting can be done into a head-shunt using the caution aspect, while a movement to the mainline would be indicated to the driver by a clear aspect. Some discs have just one face and it rotates 45^o in the vertical plane to give a clear aspect, while others have two faces rotating 90^o in the horizontal plane. Until the 1950s many disc faces were cast iron with a variety of shapes, but then standard square Perspex faces were introduced. These were subject to breakage and enamelled faces were soon introduced.

An oil lamp usually illuminates mechanical signal aspects, though there are a number electrically lit. Early tests with electric illumination of semaphore signals found the vibration of the lamp case when a signal was restored to danger caused the filament in the lamp to break. When more robust lamps were developed for motor cars, it was found these were suitable for semaphore signals. One of the first places to have electrically lit semaphore signals was Rosslare Harbour where the exposure of many of the signals to high winds in winter extinguished the paraffin lamps.

A small number of electrically operated semaphore signals remain worked by motors. The motor drives a crank arm through approximately 30° to raise or lower the signal arm. These motors were manufactured by either McKenzie Holland & Westinghouse Power Signal Co. Ltd. or the Westinghouse Brake & Saxby Signal Co. Ltd, patented in 1910 but the actual motors in use on IE are believed to date from the late 1920s. Only one of these signals is operated by a hand-generator – the Roscrea up outer home from from Ballybrophy, which is worked by a Westinghouse Brake & Saxby Signal Co. hand-generator at 110 VDC. There are a small number electrically operated semaphore signals protecting level crossings and these are battery powered using EverReady Flag Cells. These are a 1.5V dry cell wired in series to give the required 10 volts. These cells are also used in powering track-circuit indicators and ETS instruments. There are also a small number of motorised semaphore signals worked by 110V motors using main supply transformed to 110VDC.

  The remainder of this article appears in IRRS Journal number 150, published February 2003.

Copyright © 2003 by Irish Railway Record Society Limited
Revised: January 07, 2004 .