. Railroad construction. Theory and practice . Fig. iSO. 294 RAILKOAD CONSTRUCTION. §277. scribed above. ST may be measured on the ground, or it maybe computed from Eq, 88, giving the value of feet forstraight track. Since it is shghtly more for a turnout to theoutside of a curve, it may be called Then x=db = = 0. 322 foot, and aa and cc = 0. 24 foot. Wl CROSSINGS. 277. Two straight tracks. When two straight tracks crosseach other, four frogs are necessary, the angles of two of them. being supplementary to the angles of the other. Since suchcrossings are sometimes operated
. Railroad construction. Theory and practice . Fig. iSO. 294 RAILKOAD CONSTRUCTION. §277. scribed above. ST may be measured on the ground, or it maybe computed from Eq, 88, giving the value of feet forstraight track. Since it is shghtly more for a turnout to theoutside of a curve, it may be called Then x=db = = 0. 322 foot, and aa and cc = 0. 24 foot. Wl CROSSINGS. 277. Two straight tracks. When two straight tracks crosseach other, four frogs are necessary, the angles of two of them. being supplementary to the angles of the other. Since suchcrossings are sometimes operated at high speeds, they should be §278. SWITCHES AND CROSSINGS. 295 Structurally the very strongly constructed, and the angles should preferably be90° or as near that as possible. The frogs will not in generalbe stock frogs of an even number, especially if the angles arelarge, but must be made to order with the required angles asmeasured. In Fig. 157 are shown the details of such a the fillers, bolts, and guard-rails. 278. One straight and one curved track,crossing is about the same as above,but the frog angles are all Fig. 158, R is kno^\Ti, and theangle M, made by the center linesof the tracks at their point of inter-section, is also knoAvn. M = NCM. NC=Rcos M. {R - hg) cos i^i = NC + ^g; R cos Al + ig cosF^ = Similarly R-hg cos 1^ , _R cos M + ^g ~ R + ig ^ cos Fo = RcosM — hg cos F^ = R + lg R cos M — hg R-hg (129)
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