Railway signaling.

C. L. Hackett.

Railway signaling naturally divides itself into three general heads. Namely, interlocking, block signals and miscellaneous signals.

The primary reason for the use or signals on a railway is to convey information to the engine driver as to what action he is to take, and when to act. The difference between driving a locomotive and driving a horse and carriage is a question of momentum. In the case of the locomotive, a weight of several hundred or thousand tons is moving at high velocity, in the case of the carriage, a weight of a few hundred pounds is moving at low velocity, the control of the one is only approximate except through the lapse of a considerable interval of time, while the other Is practically under instant control. Signaling has developed two types of signals, which are known as, a home signal and a distant signal. A home signal is a signal located along side of the track marking a definite point beyond which the engine driver must not proceed, unless the signal indicates that he can do so. As noted above, it is physically impossible to stop a train moving at any considerable speed instantly. therefore if the train is to be stopped before it passes the home signal, some preliminary information must be conveyed to the driver, as to what indication will be presented to him by the home signal. The means employed is the distant signal, which is set in advance or the home, a distance depending on the braking distance of the highest speed trains, and is simply a repeater of the home. When the driver finds a distant signal indicating that the home signal is at the stop position, he can apply brakes and bring his train to a stop before he reaches the home signal. If the distant signal is Indicating clear the home signal must also be indicating clear.

In modern signaling the semaphore has come into general favor, as giving the best results with unfavorable weather conditions, and changing backgrounds. The Indications are given by the arm of the semaphore, the stop indication by the arm in the horizontal position, and the proceed indication by the arm inclined. Until recently the distant signal arm was distinguished from the home by having a V-shaped notch cut out of the end. The indications of the distant signal were the same as the home, that is the horizontal position of the distant arm indicated caution (that the home signal arm was at stop), the inclined position of the distant arm indicated that the home signal arm indicated clear. There is a confusion here quite apparent as with the home arm horizontal an indication is given that the engineer must not proceed beyond the signal, whereas the horizontal position of the distant blade indicated caution, "proceed but be prepared to stop at the home signal," and the only distinguishing mark for the distant arm is the V-shaped notch, which is not distinguishable at any distance nor in all weathers, consequently there are serious objections to this horizontal indication having two possible meanings. The latest practice is to have each arm capable of giving three unmistakable indications, i.e., horizontal, meaning stop. inclined at an angle of 45 degrees, caution, and vertical, meaning proceed. This is more consistent, and it is impossible to mistake the indication.

The fundamental principle underlying the construction of signals, is that a failure in any part should cause the arm of the semaphore to assume the horizontal position, Indicating stop. The common practice in America has been to give the indication by moving the arm from the horizontal to an inclined position below the point of support. This necessitates the use or a heavy counterweight to bring the arm back to the horizontal should any part of the signal break; naturally the accumulation of ice and snow on the arm itself would tend to offset this counterweight, and there are cases where such accumulation has been sufficient to hold the signal clear, when it should have returned to the horizontal. The German practice has always been to move the arm above the point of support, thus doing away with the heavy counter weight, and with this still further advantage that any accumulation of snow or ice on the blade tends to bring it back to the horizontal. This practice has found favor among the American signal engineers, and also is being used on the western lines of the C.P.R. and C.N.R. This is unquestionably a move in the right direction, and has everything to commend it.

While the day indications or a signal are given by position, the night indications are given by colors. Red has always [line of text missing from original]position, but for the other indications, practice has differed on different roads. The different colors are obtained by means of shutters of colored glass which are moved in front or an oil lamp attached to the signal mast. These colored glasses are fastened into the same casting to which the arm giving the day indications is attached, each indication or the arm has then a corresponding color indication. It is essential if the principle of signal construction above referred to, is to be carried out, that the day indications and the night indications should be given by the same mechanism; that is, it should not be possible to give an indication for "proceed" with the arm, without at the same time, and by the same means giving the proceed indication with the proper color. There are a good many signals in use in Canada to-day which do not conform to this requirement. The night indication in these, is given by rotating the lamp on its vertical axis, while by means or a pinion gear the arm is made to move. It is under these circumstances easy to conceive of a condition where the night indication would be one thing and the day indication the opposite. This becomes particularly dangerous when we realize that at night, when the engineer gets close up to the signal, the head light of his engine would illuminate the arm, and there are very few engineers who finding the arm indicating clear, would not accept this as sufficient authority to proceed, even though the light on the signal as he approached showed red.

With regard to the question of the proper colors to use for the night indications, as stated above, practice has differed in this respect. Some roads use white for the clear indication (white in this case meaning that the lamp flame is not covered by any colored glass), and green for the caution indication of the distant signal. On the other hand, some roads use green for the clear or proceed indication, and orange for the caution. It we bear in mind again the principle of construction, it is not difficult to arrive at the conclusion that all night indications should be given by some distinctive color, and in no case should the flame itself be used, except as a stop indication. For if the white indication is used, a broken colored glass would give this indication. Up to the present the only colors with sufficient range to be used as night indications are the red, green and orange. Another essential point to be remembered in connection with signalling is that it must be made impossible for any of the indications except the stop indication, to be displayed except by an authorized means. That is if the signal is operated by means of levers, then by means of the lever only can any indication be made. This necessitates the use of a rigid connection between lever and signal, or if wire is used there must be a back and front wire, if only a single wire is used to pull the signal clear, any unauthorized person could clear the signal which is manifestly an unsafe condition.

The Standard Code definition or interlocking is as follows:—An arrangement of switch, lock and signal appliances so interconnected that their movements must succeed each other in a predetermined order. Interlocking in Canada up to the present has been confined to a great extent to the protection of the crossing of two railways at grade. This is by no means its only possible application, and indeed is probably the least important of its uses. It finds its greatest economy in terminals, junctions, and at points where a great many switches are grouped together, at such points all the switches can be handled from a central point by one or two towermen, with absolute safety to the trains, and with the greatest amount of expedition.

Under the law in Canada, all trains approaching a grade crossing with another railway, are required to come to a stop before proceeding over the crossing, unless the crossing is protected by interlocking. Aside from the safety afforded by interlocking the crossing, it can be shown that there is an actual saving in operating expense when the trains reach a certain number. Henderson, in his Cost of Locomotive Operation, estimates that it costs in the neighborhood of 65¢ to stop a train and again accelerate it to its original speed.

(Continued in next issue.)

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