Part 17

It would be an interesting study, were there space, to follow the possible and proper combinations of movements to pass trains over the various tracks. It will be seen that, by concentrating the levers which move switches and signals in one place and interlocking them, it is made mechanically impossible for a signalman to give a signal which would lead to a collision or a derailment within the region under his control. The only danger at such points is that an engineer may overrun the signals. This description of the objects and the capacity of the system of interlocking is no fancy sketch. The system has been in use for many years, doing just what has been here described, and more. A recent close estimate gave the number of interlocked levers now in use in the United States as about eight thousand, and the number is rapidly increasing. Recent official reports showed that in Great Britain and Ireland there were thirty-eight thousand cases in which a passenger line was connected with or crossed by another line, siding, or cross-over. In eighty-nine per cent. of these cases the levers operating the switches and protecting signals were interlocked.

The example of interlocking which has been given is one of the simplest; the principle is capable of almost indefinite expansion, and any one lever may be made to lock any one or more levers among hundreds in the same frame. The greatest number of levers assembled in any one signal-tower in this country is one hundred and sixteen, at the Grand Central Station in New York. In the London Bridge tower there are two hundred and eighty levers. This is probably the greatest number in any one tower in the world. All of these levers may be more or less interlocked. The same principle is applied to the locking of two levers at a single switch, and to the protection of drawbridges and highway crossings.

The mechanism by which the interlocking is done is strong and comparatively simple, but a detailed description of it seems out of place here. Two levers from a Saxby & Farmer machine are shown on page 204, with lever _A_ normal and _B_ reversed. The locking mechanism is in front of the levers, and is actuated not by the levers themselves, but by their catch-rods. It follows that it is not the actual movement of a signal which prevents the movement of other signals, or of switches, but it is the intention to move that signal. This principle of "preliminary locking" is one of great importance.

Switches and signals are often worked at such distances from the tower that it is impossible for the operator to know whether or not the movement contemplated has taken place. The British Board of Trade does not permit switches to be worked more than 750 feet away. In this country there is no limit, but probably 800 feet is very rarely exceeded. Signals are worked in England up to 3,000 or 3,500 feet very commonly, and they are even worked a mile away, but not satisfactorily. This is with direct mechanical connection, by rod or wire, from the levers. It is obvious that a break in the connections between the lever and the switch or signal might take place, and the lever be pulled over, without having produced the corresponding movement at the far end. The locking mechanism in the tower would not be affected by such an accident, and consequently conflicting signals might be given. Even this contingency is provided against with almost perfect safety. If a signal connection breaks, the signal is counter-weighted to go to danger. The worst that can happen is to delay traffic. If a switch connection breaks, the locking-bolt, in the latest form of facing-point lock, will not enter the hole in the switch-rod, and consequently warning is given in the tower that the switch has not moved. Electric annunciators are often placed in the signal-tower, to show on a board before the operator whether or not the movements of switches and signals have taken place.

Considerable work must be done in the movement of each lever. The ground connections must be put down with great care, as nearly straight and level as may be, well drained, and protected from ice and snow. All of these difficulties have been overcome in a beautiful pneumatic interlocking apparatus which has been introduced within the last two or three years. In this system the motive power is compressed air. Near each switch is a small cylinder, containing a piston which is attached directly to the switch movement. Compressed air admitted to one side or the other of this piston moves the switch one way or the other. But, as it would take some time for the necessary quantity of air to flow from the signal-tower to a distant switch, a small reservoir is placed near the switch, and the air from this reservoir is admitted to one end or the other of the switch cylinder according to the position of a valve. For transmitting the motion from the tower to the valve compressed air might be used, but, as air is elastic, a quicker movement is got by using in the pipes some liquid which does not readily freeze, and which, being practically non-compressible, transmits an impulse given at one end almost instantly to the other. The signals are worked in essentially the same manner as the switches, except that the pneumatic valves are moved by electricity. The tower apparatus of a pneumatic system in the yard of the Pennsylvania Railroad at Pittsburg is shown in the engraving opposite. In the front of the apparatus is seen a rank of small handles, which can be turned from side to side with as much ease as the keys of a piano can be depressed. Turning one of these handles admits compressed air to the end of a pipe containing liquid. Instantly the pressure is transmitted 500 or 1,000 feet to the valve at the switch to be moved. The small levers are interlocked perfectly, and in that particular perform the duties of the ordinary machine. A model of the tracks controlled is placed before the operator, showing the switches and signals, and when a movement is made on the ground it is at once repeated back by electricity and duplicated on the model. This beautiful system is due to the same genius that gave us the perfected air-brake and the triple valve, and is the greatest improvement that has been made in interlocking in the last dozen years.

If the reader has grasped the full significance of interlocking, he understands that it makes it impossible to give a signal that would lead to a collision or to a derailment at a misplaced switch. The worst that a stupid, or drunken, or malicious signalman could do would be to delay traffic, if the signals were obeyed. Here comes in the failing case. The brake-power may be insufficient to stop a train after a danger signal is given. That is a rare occurrence, but may happen. The engineer may not see the danger signal because of fog, or he may carelessly run past it. Provision against a failure to see and to obey a signal may be made by placing on the track a torpedo, which will explode with a loud report when struck by a wheel. The use of hand-torpedoes in fogs, and for emergencies in places unprovided with fixed signals, is very common. These are little disks filled with a detonating powder, and provided with tin straps that are bent down to clasp over the top of the rail. A simple and very efficient torpedo machine, which has been used for some years on the Manhattan Elevated and elsewhere, is here shown. This machine has a magazine holding five torpedoes. It is connected to a signal-lever in such a way that, when the signal is put to danger, one torpedo is placed in a position to be exploded by the first passing wheel. When the signal returns to the clear position the torpedo, if unexploded, is withdrawn to the magazine. If the torpedo is exploded another one takes its place at the next movement of the signal-lever. One of these machines on the Elevated Road moves about five thousand times every day. In such a case a torpedo would soon be worn out if it was not exploded or frequently changed. When this apparatus is in operation, an unmistakable alarm is at once given to the engineer and to others if a danger signal is passed. On the Manhattan Elevated lines an engineman who overruns a danger signal and can show no good reason for it is suspended for the first offence, and discharged for the second. The torpedo makes it impossible for him to escape detection.

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The second great class of signals comprises those which are intended to keep fixed intervals of space between trains running on the same track. These are block signals. The block system is used on a few of the railroads of the United States which have the heaviest and fastest traffic. Much the most common practice in this country, however, is to run trains by time intervals, and under the constant control of the train despatcher. In England the block system is almost universal. About ninety per cent. of all the passenger lines of that country are worked under the absolute block system.

When the block system is not used, it is quite common to protect particularly dangerous points, such as curves and deep cuts, by stationing watchmen there with flags or with some form of fixed signal. The watchman can notify an approaching engine-runner that a preceding train has or has not passed beyond his own range of vision; or can notify him that it has been gone a certain time. Travellers by the Philadelphia & Reading must have noticed the queer structures, with revolving vanes on top, looking like a feeble sort of windmill, which appear in positions to command a view of cuts, curves, etc. These are examples of the devices for local protection. The non-automatic block signal develops naturally from the protection of scattered points. Instead of placing watchmen at points of especial danger, they are placed at regular intervals of one mile, two miles, or five miles. Instead of the watchman looking to see that a train has disappeared from his field of vision before he lets another train pass, he uses the eyes of the next watchman ahead, who telegraphs back that the train has passed his station. Suppose A, B, and C to be three block-signal stations placed at intervals of two miles. When a train passes A, the operator at that point at once puts a signal to danger behind it. This signal stands at danger until the train passes B, and the operator puts his signal to danger, and telegraphs back to A to announce that train No. 1 has passed out of the block A B, and is protected by the signal at B. Then, and not until then, the operator clears the signal at A and allows train No. 2 to enter the block. Meanwhile train No. 1 is proceeding through the block B C, its rear protected at B; and the same sequence of events happens when it arrives at C as happened at B. This is the simplest form of block signalling. In the more elaborate form there are at each block-station three signals--the distant, the home, and the starting. The signals are often electrically interlocked, from one station to another, in such a way that it is mechanically impossible for the operator at A to give a signal for a train to pass that station until the signal at B has been put to danger behind the preceding train.

A B C -----------------------------

It is seen that no two trains can be in the same block and on the same track at the same time. If all run at a uniform speed, they will be kept just the length of a block apart. If No. 2 is faster than No. 1, it will arrive at B before No. 1 gets to C, but will have to wait there. The block system, therefore, while it gives security, does not always facilitate traffic. The longer the blocks the greater will be the delay to trains; but the shorter the blocks, the greater the cost of establishment, maintenance, and operation.

Various systems have been contrived to have block signals displayed automatically by the passage of trains. This, if it can be done reliably, will do away with the wages of part of the operators, and will also eliminate the dangers arising from human carelessness. But there are very great objections to relying solely upon the automatic action of signals, and automatic block signals are little used except as auxiliary to a system employing operators also. So used, they are of decided advantage, as they make sure that a danger signal is set behind every train in spite of the operator, and that it cannot be again set to the all-clear position till the train has passed out of the block. All this is accomplished by electricity.

Brakes, interlocking, and the apparatus of signalling have been considered at length because they are very much the most important of all the appliances which go to increase the safety of operating railroads. They act chiefly to prevent collisions, but often prevent or mitigate accidents from derailments and other causes. Of all train-accidents happening in the last sixteen years, over one-third have been from collisions, and more than one-half from derailments.

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After brakes and signals, the devices next in importance as means of saving life are those for the protection of highway crossings at the grade of railroads. In years to come, as wealth increases and as traffic becomes more crowded, we may suppose there will be few such crossings; but their abolition must be slow, and meantime the loss of life at them is great. The most accurate and complete statistics bearing on this matter are those collected by the Railroad Commissioners of Massachusetts. In 1888, of all those killed in the operation of the railroads of the State, seven per cent. were passengers, thirty-three per cent. were employees, and sixty per cent. were others. The others include trespassers, forty-seven per cent.; and killed at grade crossings, eleven per cent. More trespassers were killed than any other class; but the deaths at highway crossings considerably exceeded those among passengers. The difficulty of preventing this class of accidents is strikingly shown by the fact that, of all crossing accidents, forty-two per cent. were due to the victims' disregard of warnings given by closed gates or flags. It is evident that the efforts of the railroad companies to save people's lives at crossings are largely nullified by the carelessness of the public, and the lack of proper laws to punish those who venture upon railroad tracks when they should keep off them. Still, it remains the duty and the policy of the railroads to protect street crossings by all practicable means. The best protection is afforded by gates with watchmen, and of all forms of gate the most common, because it is the simplest and most convenient to operate, is the familiar arm-gate. This is usually worked by a man turning a crank, but it is also worked by compressed air. On this page is shown a group of gates worked from an elevated cabin by a mechanical connection. A bell fixed at a crossing, to be rung by an approaching train, is a very useful auxiliary to gates and to watchmen with flags, and is considerably used where the traffic does not warrant the expense of maintaining a watchman. There are several good devices of this sort, either electric or magneto-electric. One of the latter class has a lever alongside the rail, which is depressed by each wheel that passes over it. This lever is geared to a fly-wheel, which is set rapidly revolving and causes an armature to revolve in the field of a magnet, and thus generates a current and rings a gong, precisely as is done with the familiar magnetic bell used with the telephone.

About thirteen per cent. of the train-accidents in the United States, in the last sixteen years, were derailments due to defects of road. These include not only defective rails, switches, and frogs, but bridge wrecks. There are, however, few devices used in the track, other than those already mentioned, that can be called safety appliances. This class of accidents is to be provided against only by good material, good workmanship, and unceasing care. Many so-called safety switches and safety frogs are offered to railroad officers, but those actually in wide use are confined to a very few standard forms. The split-switch, which is shown in the engravings on pages 206 and 207, has gradually replaced the old stub-switch, as well as most of the "safety" switches that have been from time to time introduced; although the stub-switch is still in considerable use in yards where movements are slow, and in the main tracks of the less progressive roads. It consists of a pair of moving rails the ends of which are brought opposite to the ends of the main-line rails, or to those of the turnout, as the case may be. It follows that but one of these tracks is continuous at any one time, and a train reaching the switch by the other track must be derailed. The distressing accident which happened at Rio, Wis., in 1886, where seventeen people lost their lives, was a derailment of this sort. Since that time the railroad on which the accident happened has taken out all stub-switches on thousands of miles of main-line track. The split-switch provides against such derailments, for if the switch is set for the turnout, and a train approaches it from the main line in the "trailing" direction, the flanges of the wheels move the switch-rails to make the track continuous. The terms "facing" and "trailing," as applied to switches, are almost self-explanatory. If a train approaches toward the points of the moving rails, the switch is said to be facing. If it runs through the switch from the rear of the moving rails, the switch is said to be trailing. This will be made clear by reference to the illustration on page 206. If a train were coming from the bridge, the first switch reached by it would be a trailing and the second a facing switch. In the newspaper reports an accident will very often be assigned to one of two causes, failure of the air-brakes or spreading of the rails. The chances are that it will be found on investigation to be due to neither of these causes. Those interested to maintain the credit of the air-brake or of the track department are not often on the ground when the reporter gets his information, and the temptation is always great to shift the responsibility to the shoulders of the absent. Probably the displacement of the rail will have taken place after the derailment; but rails do sometimes spread. Loose spikes and rotten ties allow the outer edge of the rail-flange to sink into the wood, and the rail to roll outward enough to let the wheels drop. Sound ties are the first safeguard against such accidents. Metal plates under the rails are useful also; but one of the most efficient means of preventing displacement of the rails is the interlocking bolt shown above. These bolts cross in the timber, and slots cut in the two bolts engage with each other in such a way that when the nuts are screwed down on the rail-flange it is impossible to pull the bolts out. They can only be moved by tearing through the wood contained in the angle between them. This bolt is much used on bridges and trestles, where it is of vital importance that the rails should be held in place and no part of the floor broken.

In 1853 an express train went through an open draw at South Norwalk, Conn., and forty-six lives were lost. This, one of the most serious railroad accidents that ever happened, is still remembered as an historical calamity. The bridge which stands on the same site is shown opposite. In May, 1888, a west-bound express train, consisting of an engine and seven cars, was derailed just as it was entering the draw-span. The train ran three hundred feet on the sleepers before it was stopped. Then it was found that all of the driving-wheels of the engine had regained the rails, but all the other wheels were off, except those of two sleeping-cars in the rear. This was a remarkable escape from a bad accident, and much of the credit of it has been given to the interlocking bolts with which the rails were fastened. They are supposed to have prevented the rails being crowded aside, and thus to have made possible the rerailing of the engine. Besides, they helped the oak guard-timbers to hold the ties in place. The destruction of a bridge in an accident frequently begins by the ties bunching in front of the wheels and allowing the wheels to drop through and strike the floor-beams below. For this reason guard-timbers, notched down over the ties, should always be used.

The traveller will have noticed, on all bridges of various roads, two rails placed inside the track-rails, and curved to meet in a point at either end of the bridge. These are known as inside guard-rails, and their function is to keep derailed trucks in line till the train can be stopped. Besides the bunching of the ties, there is danger in a bridge derailment that a truck may swing around and strike one of the trusses. Then the bridge is very likely to be wrecked. A further provision for the protection of bridges is the rerailing frog invented by the late Charles Latimer, whose name is dear to railroad men all over America. This consists of a pair of castings combined with inside guard-rails, designed to raise the derailed wheels and guide them on to the rails. There is no doubt that it has prevented several wrecks, although it has never been widely used. The subject of bridges should not be left without a word of explanation of the stout timber-posts often seen at either end placed in line with the trusses. These are designed to stop any derailed vehicle which might otherwise strike against and destroy a truss.

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There is one track-fixture that has no duty or value except as it promotes safety. It helps only one humble class of railroad employees. That device is the foot-guard. At all places where two rails cross or approach each other, as at frogs and guard-rails, dangerous boot-jacks are formed by the rail-heads. The overhang of the heads of the rail makes it easy for one to so fasten his foot in one of those boot-jacks that it is hard to get it out. If a man finds himself in this position in front of an approaching train, he sometimes has the alternative of standing up to be struck by the engine or lying down and having his foot cut off. Fortunately this class of accidents is comparatively rare; probably not more than two or three per cent. of all deaths and injuries to passengers and employees is caused in this way. Nevertheless, the means of guarding against accidents of this class is so cheap that it should be more generally adopted than it is. It consists simply in partly filling the space between the rail-heads by putting in wooden blocks or strips of metal, or even packing with cinders, gravel, or any sort of ballast. Various wooden and metal foot-guards have been patented. They are all too simple to require description.

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