Cableways.— In some places an overhead cableway can be used to great advantage in erecting or building a bridge or in transporting supplies across a stream that vehicles cannot cross. There are two classes, the ordinary cableway and the balanced cable crane. The first form can be quickly rigged.if large trees are close to the bank and is very convenient when the load does not have to come in to the very foot of the supports. If towers must be used to support the cable they are difficult to erect and the material is too heavy to carry in a field equipment. A considerably longer span is always necessary than the actual width of the stream and the load must be pulled up hill over one-half of its journey and is only stable at the lowest point in the catenary. The balanced cable crane, on the other hand, can carry loads farther inshore than its points of support; the stress in the cable is constant whatever the position of the load and only sufficient force to overcome friction is required to move the load along the cable. The key to the construction of this cableway is that the length of the cable must be such that both counterweights cannot rest on the ground at the same time. The automatic rising and fall ing of the counterweights as the position of the load on the cableway changes keeps the angles of the cable at the load symmetrical with the action line of gravity and hence the load at any point on the cable.
Turnouts and turnout is a curved track by means of which cars are moved from one track to another. The special parts of a turnout are the frog and the switch and the guard rails. The term %witch° is frequently applied to the part of a turnout from the point of switch to include the frog. The switch proper may be either a stub or a split switch. The latter is the form now generally used. Stub switches are only used on unimportant lines or in yards. A double turnout is one where two tracks diverge from the main line, either on the same side or on opposite sides. In a turnout from a curve, the curvature of the turnout for a given frog is different from the curve of turnout from a tangent, and is equal to the curve of the main line plus the curve of the turnout from a tangent for a cor responding frog. The lengths of rail would not be exactly the same on the turnout from a curve as they would be on a turnout from a tangent. On account of this and because of the desirability of having a number of turn outs ready for use at any time, it is best to lo sate all turnouts on tangents, where practicable. These ready-made turnouts should include all material for the turnout, as shown in bill of material, so that by leaving out an exact number of 30-foot rails the track-laying can be con tinued; and when the turnout is put in place the opening left will be exactly filled. Frogs and switches can either be bought outright from equipment companies or can be made in. the shops.
The curves used in laying out turnouts and crossovers are ordinarily arcs of circles and are usually simple curves. It may happen that no frog is at hand, in laying out a double turnout, that will permits a simple curve to be run from the heel of the switch to beyond the farthest frog. In this case, use the frog that will require the sharpest curve as the crotch frog, allowing the flatter curve to he between the two frogs.
Facing and Trailing These terms apply particularly to the switches of crossovers on a double-track line. A trailing point is one which the trains move over from the point of frog to the point of switch; and a facing point is one which the trains move over from the point of switch to the point of frog. A con
sideration of the drawing will show the advan tage of trailing points, in that if the switch is set wrong the train will run through it, forcing the switch points aside. This will break the switch, but the train will not be damaged. On some roads the policy is to have all main line switches trailing points and although this requires n little more time in switching cars or going into a siding, it is safer.
Switch switch stand is a mech anism by means of which the switch points are moved. The largest kind is more readily seen than the smallest ane and would be used in cases where the engineman must be able to note a mis setting of the switch. The smallest kind is the kind used in the interlocking plant, where it is next to impossible for a switch to be set wrong and the engineman not be notified of it long be fore he reaches the switch. The middle type is one that is commonly used in yards. Economy of space and weight might dictate the use of the smaller switch in all cases on a supply road. For stub switches these stands should be on the engineman's side approaching in a facing di rection. For split switches they should be on the side of the turnout.
Storage The number and length of these tracks depend upon the importance of the station, the number of depot storehouses that may be located at that point, etc. A star0 of these items shows that each must be dealt with as it arises and as it is impossible to tell how important a station may become at any future time, available track room will be left for additional loading platforms and storage tracks. In locating the storage tracks, room should be left between the various tracks so that at least one and preferably two lines of wagons can drive in and receive freight from cars on the storage tracks.
Tunnels.— Few serious difficulties are met in tunneling operations except in subaqueous work, where the nature of the soil is largely unknown, and the work may have to encounter faults in rocks or springs or quicksands in the earth; or the roof formed by a river bed may give way and tons of water may be precipitated into the workings below. Under these condi tions work beneath the water has become a new science which has its own special class of work men, tools and devices adapted practically for its own purposes as described elsewhere in this work under TUNNELS AND TUNNELING (q.v.). See related articles Ant BRAKE; BLOCK SIGNAL SYSTEM; BRIDGE CONSTRUCTION, AMERICAN; BRIDGE CONSTRUCTION, MODERN METHODS OF; BRIDGE DESIGNS, RAILWAY; CAR BUILDING IN DUSTRY; LOCOMOTIVE; LOCOMOTIVE INDUSTRY; RAILWAYS, ELEVATED; TUNNELS AND TUN NELING.
Bibliography.—Acworth, W. M., of Railway Economics (London 1905) ; Adams, C. F., : Their Origin and Problems> (New York 1878) ; Byers, M. L. of Railway Operation) (New 'York 1908) ; Crandall and Barnes, (Railroad Construction> (New York 1913) ; Hadley, A. T., (Railroad Transportation : Its History and Its Laws> (New York 1899) ; Haines, H. S., (Railway Comorations as Public Servants> (New York 1907) ; Morris R., (Railroad Administration) (New York 1911) ; Paine, C., (The Elements of Railroading> (New York 1885) ; Welling ton, (The Economic Theory of Railway Loca tion> (5th ed., New York 1896) ; Wright, R. V., and London, A. C. (Car Builders' Dictionary) (9th ed, New York 1919).