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Automatic Signalling
Keep the Trains Moving

(By W. H. H. Grapes , Grad. I.E.E., Automatic Signalling Inspector, N.Z. Railways)

I do not think it would be out of place at the present juncture to broadcast a little of what the Signalling Branch of the New Zealand Railways is doing. Now one of the most important factors in a railway system is the signalling, as without efficient signalling trains cannot move with any semblance of order, or regularity. The importance of other factors is fully recognised, but without the signal to guide and protect the movements of trains their efforts would be useless.

Whilst confining this article to automatic and power signalling, I would like in passing to refer to an old and staunch friend, “mechanical interlocking and signalling.” This system has stood the test of time and proved true right down through the periods of the railway world and, but for it, Great Britain could not, to-day, effectively control the immense traffic carried upon her bewildering network of railways. In quoting from a recent press announcement I think it is valuable testimony that during last year 1,700,000,000 passengers were carried without the loss of a single life through any cause due to the signalling and interlocking arrangements. Great Britain has always been the home of mechanical interlocking and signalling, and to-day stands paramount in that respect.

Automatic signalling has never been an experiment, as from the very first introduction the system was a success. It has progressed by leaps and bounds. This modern era dates back to 1903 and since that date the mechanical has steadily been giving way to the electrically worked systems. During the early stages of electric signalling, direct current was used, both by generation and battery power, and this to a certain extent retarded the progress and limited the scope of the systems as to distance of supply. At the same time the safety factor was reduced by the possible influences of foreign currents. This was soon changed by the application of alternating current which removed all these handicaps, and has been a success since its adoption, it being possible to design all appliances to operate on this form of supply, and not only to equip large yards and stations, but also to transmit energy to long distances enabling signal engineers to extend the protection and increased capacity which electric signalling provides. Upon the introduction of the three position automatic signalling it was soon found that the capacity of running lines was considerably increased and the “safety factor” was raised, thus satisfying the paramount requirement of any signalling scheme that “the signal indications must be reliable.”

The system which is in use on the New Zealand Railways is based on the A.P.B. or Absolute Permissive Block, meaning the absolute spacing of trains from crossing loop to crossing loop and permissive spacing for following movements, but with a number of modifications introduced by the signal and electrical branch of the New Zealand Railways which makes it an ideal system and, for a given expenditure, provides greater safety and more capacity than any other form of signalling.

The main basis of this system is the “Track Circuit.” By its means every part of the railway track between signals or in yards where electric power signalling is installed is electrically alive. Power is fed at one end to the rails, flows thereon to the next signal and is then taken to a relay, the end portions of track between signals being insulated by wooden fishplates and the rails from end to end being bonded together. This relay is called a “track relay,” and is really the heart of the system. Without its aid the continuity of the system fails as its functions are to denote when a train is occupying its track, cut off all feed, and place signals at “Danger.”

The main purpose of automatic block signals is the spacing of trains and the supplying of information to the enginedriver as to the presence of other trains which are about to interfere with his movements or speed, this information only being possible when the position of all switches, etc., is correct and the track clear.

The spacing of signals is a matter to be decided upon so as to obtain the utmost running value from the traffic offering, and for double line working it is quite possible to arrange one to three minute intervals between trains according to speed.

It is the moving trains that earn the revenue, therefore, the quicker a train completes its journey due to increased signalling facilities the quicker the rolling stock may be again utilised for revenue earning purposes.

Faster running, increased services, and safety factor 100 per cent. can easily be claimed for three position automatic signalling. Other advantages are, the saving of staff, which means page 73 reducing the human element. This reduces the possibility of error and provides simplicity of maintenance. This does not mean that it is a Tom, Dick or Harry job, but that once the installation is complete, renewals are nil for a considerable period; the principal duty of the maintainer being to tell by expert knowledge that all is functioning properly, all faults giving danger indications, and the system being at all times ready, with everything normal, to accept and protect emergency traffic without any special advice or preparation.

The first installation on the New Zealand Railways was the double line between Lambton Station (Wellington) and Lower Hutt, which has proved an unqualified success. This was the means of saving the services of eight signalmen as all the existing signal boxes were converted into switch-out boxes, (it being possible to switch in at a few moments notice and this operation being carried out by any member of the station or train staff) and giving a spacing movement of trains to 3/4-mile. This installation was immediately followed by equipping the single line from Lower Hutt to Upper Hutt, superseding the electric tablet system and releasing the services of another eight men.

The signals used for both these installations were the three position upper quadrant semaphore arm signals giving a “danger” indication in the horizontal position, caution indication in the 45° position, and clear indication in the 90° position. This system provides for complete head page 74 on protection from crossing loop to crossing loop and permits following movements with the minimum allowable spacing between trains. Hand in hand with this is the train control telephone system, which provides for a telephone in each positive departure signal giving instant communication with the train control officer in charge, thus any alteration of train running can be quickly made direct with the crew of the train.

The Race traffic working under this system between Trentham and Lambton has proved to be ideal, it being possible to despatch trains, if necessary, at intervals of one minute 25 seconds. The writer noticed on a recent date the flexibility which this system provides. This was as follows:—Owing to slips in the Manawatu Gorge it was necessary to run the Napier expresses via the Wairarapa instead of the Manawatu line, and a race train had just cleared the signal in advance of Trentham when the “down” Napier whistled; the racecourse loop points were placed normal, the main down departure signal cleared, and the Napier express ran through at slightly reduced speed, clearing the signal in advance in plenty of time to permit the next following race train to leave on time. Similar uninterrupted sequence of traffic would have been impossible under the Tablet system.

This system also gives an indication to an engineman of an opposing train to cross, as when two trains are approaching a crossing loop, from opposite directions, caution signals are displayed on the last automatic signals nearest the loop. These signals being for the time distant signals, enable the arrival signals to be approached with trains under complete control and thus safeguard the possibility of over-running signals.

Not only does this system apply to working between stations, but it also extends to those stations and goods yards which are termed electric power interlockings, giving the fullest elasticity and protection of movements into, out of, or within the yard; the whole operation being controlled from a small lever frame situated in the Stationmaster's or other convenient office, it not being necessary to build any special signal to house the frame.

Another advantage of the system is that all members of the staff who have to use velocipedes on portions of the line where there are tunnels and heavy cuttings, after becoming acquainted with the working, can, at a glance, find out whether there is a train opposing or following them.

For those readers who are not yet acquainted with this advantage I will detail a few points to be observed. If you are going along and both “up” and “down” signals are at clear (green) the section is clear of all traffic—except velocipedes or material trolleys which do not affect the signal indications and which, in the writer's opinion and backed up by one or two practical instances, call for constant vigilance. If the signals you are facing change to red a train is in the same section and opposing you. If on passing a signal location you look back and find a red indication on the signal you have just passed, a train is following you and in the same section. (To be continued.)