Safety The greatest care must be exercised in the instalment of safety devices, as far as practicable automatic, without dis couraging watchfulness on the part of engineers and others. The plan of sealing the stopping mechanism and imposing a severe penalty for breaking the seal is an excellent one. The most carefully planned automatic devices should be provided, and no railroad train, traveling at terrific speed, and representing enormous energy, should be allowed to run without any safeguard between itself and disaster beyond the watchfulness of one man, who may be taken ill, or suffer from a temporary mental aberra tion, or may even die suddenly and unnoticed.
Curving Before any rail is spiked to its place in a curve it must be evenly bent from end to end, so that it will assure the proper curvature when lying free. This curv ing may be done by hammers, but that method is slow and the rail-curving machine is gener ally employed. This machine is made with either screw or hydraulic power, and is used for bending rails rather than for curving them. For many curves no rail-curving is necessary, the friction between the rail and the ties being sufficient to hold the rail in position. The ex tent of this flexibility depends on the weight and length of the rail, and can be found by trial. Three degrees and sharper curves usually re quire a curving of rails. Knowing the radius of the curve and the length of the rail, the middle ordinate of the rail can be taken from prepared tables. Each half of the rail, from the middle point to the ends, should also be tested for its middle ordinate to ensure uni form curvature. The middle ordinate of these half sections is one-fourth of the middle ordi nate of the entire rail.
Grade The crossing of one railroad with another at grade is a common condition. This offers a dangerous condition which may be fully protected by a system of signals, derails, etc., which enables trains to proceed over the crossing at speed and with safety. The installation requires for a single line crossing eight signals, four of which are erected about 500 feet each way from the cross ing. These four signals are called home sig nals. Beyond these, a distance of 1,500 feet or more, are located the distant signals. If we were certain that signals would be obeyed at all times we would need no further protection; but we have not yet arrived at a degree of efficiency in discipline which ensures that trains will never run by a danger signal. It is the general practice in the United States to pro vide a derail at the home signal which is opened after all signals on the route are placed at stop. This derail is an ordinary switch point and if a train attempts to proceed to the cross ing against a stop signal it is derailed. This
seems a brutal method of compelling the ob servance of a signal. Experience has demon strated, however, that the derail is a moral agent and is effective in its presence and is sel dom called upon to perform its office. A clear signal cannot be given for the crossing until the derails on the opposite route are open, and the signals on that route are in the stop posi tion and the signals cannot be pulled to the safe position on opposing routes.
The opening of a switch under a train is guarded against by the detector bar. A thin bar 55 or 60 feet long is hung in a vertical position on the outside of the rail at the switch point fixed on links clamped to the rail, and so arranged in the general scheme as to make it necessary for the operator to move this bar vertically above the rail before the switch can be unlocked or moved. If a car or train is standing on or passing over the points the bar cannot be moved because the wheels of the car prevent its rising above the rail, consequently the switch cannot be opened under the train. These bars are also provided on each side of the crossing so as to ensure against changing signals where a short or light locomotive may have passed the home signal toward the cross ing but has not passed the crossing. This con dition may be better protected by employing a track circuit between derails controlling an electric lock which ensures against change of signals until the train has passed entirely out of the limits of the derails. Where signals and switches are operated by lines of inch pipe carried on rollers and are compensated for change in temperature by what is known as a ((lazy jack)) these carriers, compensators and cranks are now usually fixed on concrete foun dations.
Draw The protection of draw bridges is perhaps more important than grade crossings and for this work the interlocking machine is employed with the home and distant signals, and where practicable derails are used. The signal cabin may be located either over the pivot pier or on the shore. To ensure safety we must ensure that before a clear signal is given the rails at each end of the draw are down in place and locked, the draw itself locked to the abutment and the turning mechanism locked and that none of these conditions can be changed so long as the signal shows clear, and in reversing the order of movement the draw cannot be opened until the signals are at danger and the signals cannot be cleared until the draw is again closed, etc. The important device in this combination is the bridge coupler for pipe lines which must be uncoupled by the operator from the cabin before the draw is opened.