Page:The New International Encyclopædia 1st ed. v. 16.djvu/752

RAILWAYS. centre of a tie. Suspended joints are by far the most common in the United States. Rails are said to be laid with square joints when the joints of the two lines of rails are opposite each other, and they are said to be laid with broken joints when the joints in one line of rails come opposite the centre portion of the rails in the other line. Broken joints are the more common in the United States. On curves the gauge of the rails is usually slightly increased, with the idea of preventing the flanges of the car wheels from binding when rounding curves, and the outer rail of the curve is elevated above the level of the inner rail to counteract the tendency of the running cars through centrifugal force to continue in a straight line when passing a curve. The amount of this elevation is greater the sharper the curve is. This same centrifugal force of the car tends to push the outer rails of curves in an outward direction or away from the inner rail, and to prevent this the outside rails on flat curves have a double set of outside spikes,

and on sharp curves braces of stamped or cast steel or iron are spiked to the tie and brace against the side of the rail. These braces are called rail braces. In many places rails develop a tendency to creep or travel along the track, due to the various forces acting upon them. The direction of this creeping may be either up or down grade, with or against the traffic, and to prevent it check plates or creeper plates are sometimes employed, which are bolted to the rail and spiked to the tie. Special forms of track construction are required at switches.





The switch is a device by which a train is directed from one track to another. An essential part of a switch is a frog. (See .) On bridges and trestles the track construction also varies somewhat from that on embankments and in cuts. Sometimes the floors of bridges are made solid and carry ballast on which the ties and rails are supported in the usual manner, but more commonly the ties are laid on the bridge stringers and carry the rails without any ballast. An essential part of railway track on bridges is a wooden or metal rail laid parallel to each of the track rails and a little distance away from them. The object of the guard rails is to restrain the free movement of derailed cars and prevent them from running off the bridge. In thickly settled districts the railway right of way is usually fenced in with fences of timber or wire, or, where a nice appearance is particularly desired, with hedges and walls of stone bearing ornamental iron railings. At grade crossings of highways and in a few other places at which cattle are liable to stray onto the track cattle guards are employed. These are of two kinds, known as pit guards and surface guards. A pit guard, as its name implies, is a wide deep pit underneath the rails which cattle will shun for obvious reasons. A surface guard is made up of sharp edged or toothed slats of wood or metal which depend for their efficiency upon the fact that in treading upon them the animal hurts its feet and withdraws from the attempted crossing.



Sidings and yards are special developments of the track system for special purposes. Sidings are provided to enable trains to pass on single-track roads and to relieve traffic on double track.