Railway signaling.

C. L. Hackett.

(Continued from November issue.)

Mr. Peabody, Signal Engineer of the Chicago & North Western Ry., after having experimented with different trains, concluded that it averaged 45¢ per train. For the sake or illustration, if we take 45¢ as the cost, it is an easy matter to determine how many trains per day will justify the expenditure necessary to install interlocking at a crossing. Fig. 1, on page 1001, shows on diagram the signaling necessary to protect a single track crossing a single track. There would be 16 levers. This sized plant insta11ed would cost $4,800, and would require a day and night towerman to operate it. The yearly cost for the plant would stand about as follows:—

Cost of interlocking		$4,800 00
Interest on cost, 4%	192 00
Depreciation, 7%	336 00
Cost of maintenance per year	240 00
Cost of operation per year	1,200 00
Total coat per year	l,968 00

Savings to be effected:—

Trains per day	14	20	25
Cost per year on account of stopping	$1,971	$2,817	$3,521
Total yearly cost of interlocking	1,968	1,968	1,968
Net savings per year	3	849	1,553
Cost of interlocking	4,800	4,800	4,800
Time required to pay for installation from saving		5 1/2 years	3 years

It is apparent then that 14 trains a day over this plant would justify its Installation, aside altogether from the saving due to Increased safety.

Interlocking Is based on the following principles. First, that a failure in any part of the apparatus will present a clear signal being displayed. Second, that the normal position of all signals is stop. Third, that a signal cannot be cleared for a train to move across the interlocking until all the switches in the route are properly set, and locked. Fourth, that a signal cleared locks all the switches. and that no switch or lock can be moved while the signal is clear. Fifth, that the signal cleared guarantees to the engineman the route, with no possibility of a move being made by any other train that could in any way foul the route given. In Canada the first three of these have been always conformed to, but the fourth (fully as essential as the other three) has not. Fig. 2, on pg. 1001, is a sketch of a plant in operation which does not. A train moving from B to C having received a clear signal no. 1 is not protected from a possible movement by a train from Q which could cause a serious side swipe at the frog A. I have seen several other plans which also have this serious loop hole, and it has been my experience that if a loop hole is left in any signaling installation it is only a question of time when some train will run into it.

In order to prevent a train running by a signal at a crossing the law requires the use of a derailing switch operating in connection with the signals. The signal can only be cleared after the derailing switch has been closed and locked. The closing of the derailing switch on one side locks the derails on the crossing line open. the idea being that it signals alone were used, it would be possible to have a train on the crossing run into by a train on the other line, should the engineer disobey the signal. Each individual interlocking plant is a problem in itself, different conditions either in track lay out or operation in itself, different treatment in the location of the signals, and this is the province of the signal engineer. The signal engineer of a large road is one of the most important officials. His knowledge and experience must be large and varied. He should be a civil engineer, and also thoroughly understand how the trains are operated, his duties, once the plant is installed, are closer allied to the operating end of the railway than to the engineering. In order for him to be able to advise what arrangement of signals will give the greatest results he must be in close touch with the officers who are responsible for the movement of the trains, otherwise his usefulness to the railway is not fully utilized.

In Fig. 1 we have the layout of a simple crossing of one single track line with another. Each derail is handled by a lever situated in a convenient building. The locks for the derails are handled by levers, and the signals by levers, all of these levers are grouped together in a frame, the interlocking between the levers being obtained by the use of cross locking operated by the levers, and held in the lever frame itself. The levers are numbered consecutively from left to right, the derail, switch, lock or signal which they operate being numbered to correspond to the lever, the connection between the levers and the functions being made by means of pipe carried on rollers, the turns in the pipe lines being made with bell cranks. The lock lever also operates what is known as a detector bar, whose function is to prevent the switch or derail being unlocked if there is a train on the track. This detector bar consists of a long bar of steel supported on a number of links pivoted to a casting attached to the base of the rail, free to move in a plane parallel to the track and inclined slightly toward the centre. When the bar is moved the links raise it above the tread of the rail. If, however, a wheel is on the rail the bar cannot be moved, as it will be held down by the wheel tread which projects beyond the rail head. This prevents the lock plunger from being withdrawn while there Is a car on the track. In the figure the interlocking between the levers would be:—

Reverse lever no.	Requires and locks levers nos.
1	2R
2	5R	10R	13N
3	4R
4	7R	12R	15N
5	6R
6	8N	11N
7	8R
8	6N	9N
9	8N	11N
10	9R
11	9N	6N
12	11R
13	10R	5R	2N
14	13R
15	12R	7R	4N
16	15R

Thus the first lever to be moved would be the derails, then their locks, then the home signal and last the distant signal, in returning the track to its former position, the order of moving the levers is just the opposite.

Block signals differ from interlocking signals only in this respect. Interlocking signals Indicate a condition of the track and switches, block signals on the other hand indicate the presence or absence of a train in or from a section length of track. They may indicate the condition of the switches also, but their function is to show whether a train can be admitted to a block system, or whether it is already occupied. The block system is a means of moving trains by means or signals, as opposed to moving trains by time table and train orders. The principle on which it is based is that two trains must not occupy the same piece of track at the same time. The line is divided Into sections, the limits of which are marked by a signal, and trains are only admitted to one of these sections by means of the signal governing that block. The length of these sections will depend on the number of trains run, their speed, and maximum length.

There are several different methods of block signaling in use. In the telegraph block system the signals are operated manually, upon Information by telegraph. This is simply a make shift and is a combination of the block system and the Standard Code and dispatching system, a combination that cannot be made if the basic principle of block signal operation is maintained. In the controlled manual block system the signals are operated manually and so constructed as to require the co-operation or the signalman at both ends of the block to display a clear signal. That is in this system the signal at the entrance end of the block is so interlocked with the signal levers at the outgoing, and that it requires the men at each end to cooperate in order to admit a train. There are several types of this system, "the block and block", ordinarily used on a double track, where head on movements are not ordinarily made, and the staff system on single track, where head on movements must be protected. In the automatic block system the signals are operated by electric, pneumatic or other agency actuated by a train, or by a certain condition affecting the use of a block. This system does not supersede the train order system of dispatching, and is not absolute, that is from its nature it is necessary where automatics are used to insert the rule, that an engineer finding a block signal indicating stop, must bring his train to a stop at the signal and then proceed, under caution. If this rule is not used the train men would have to flag through the block; the introduction of this rule makes the automatic a permissive signal.

Miscellaneous signals comprise train order signals, used at stations to indicate to the runner whether he is to stop for orders or not. Station signals, used to protect trains standing at stations where no block system is in use. Outlying switch signals used to indicate to a runner, whether or not the main line switch is properly set for him to proceed. Highway crossing signals, used to warn the public at a highway or the approach of a train. In the case or station signals, it is futile to simply put up a home signal of 1,600 or 2,000 ft. from a station, and expect that this will protect the station. It will not. If a train Is running at 45 or 50 miles an hour, as pointed out above. It would be impossible for the driver to stop at the signal, and if the signal does not mark the point beyond which he must not go, what does mark this? In order for a station signal to be effective it must have a distant signal working in conjunction with it. I have in mind a condition which I saw some time ago at a station, where a freight train had stopped. The caboose was perhaps some 60 ft. inside of the station signal, which was indicating "stop". Approaching the signal at this point there Is a sharp curve, a following freight came round the curve and did not have time to stop before it ran into the caboose of the standing train. A distant signal would have given the proper preliminary information. The fundamental principle that must be kept ever in mind in signaling is that a failure in any or the parts must produce the stop indication. Thus when we put up a signal at a highway crossing to protect the public using that crossing, it is here just as necessary to keep this principle In view as it is at an interlocking plant. The crossing signal should be so constructed that if any thing falls, the signal should give a positive stop indication to the highway. Most of the highway crossing signals simply consist of a bell. When the bell rings the public understand that a train is approaching the crossing, when the bell is silent it is perfectly safe for them to cross the tracks. This is evidently wrong, a broken wire, a discharged battery or one of several things may happen to prevent the bell ringing, yet the non-ringing of the bell is an indication in the proceed position, nor does the addition of a light in connection with the bell improve matters. The light is run usually by the same source or power as the bell; anything that will cause the bell to fail will also cause the light to do likewise. A crossing signal to be dependable must be built on the same principle as a signal. It should have a visible stop indication that will show stop should any break occur. The bell is a good adjunct to such a signal, but the visible indication which will take up the stop position by gravity is essential.

The foregoing paper was read before the Central Railway and Engineering Club, recently.

Fig. 1

Fig. 2

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