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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.
Crossing Gates worked by Mechanical Connection from the Cabin.
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.
