TRACK WORK 251 



may be dropped. The formulas for sin M and BE then become, 

 respectively, 



sin M- 



-V? 



and BE = 



The preceding formulas apply only to stub switches; to 

 apply them to point switches, proceed as follows: Having 

 located one frog point K of the point-switch turnout, measure 

 back from K the lead KB for a stub-switch turnout taken from 

 the table, and from the point R of the center line opposite B 

 run in the curve RmZ to the point of reversal. Then, measure 

 off the distance BE = 2'\lar\ and from the point B' opposite 

 to E lay off the stub-switch lead B'K' to locate the second point 

 of frog K'. Then run in the center-line curve R'Z. The two 

 frog points and the reversed curve mZm' are thus located. 

 Finally, measure back from K and K' the distances Kb = K'b' 

 equal to the lead for point switches, to locate the toes of the 

 point switches at b and b' ', and complete the location of these 

 switches as explained under Laying Out Turnouts. 



It is evident that the whole length of the cross-over when 

 point switches are employed is be = b'e' = BE 2XBb = 2^ar 

 -2XBb. Therefore. 



be = b'e' = 2\ar 2 X (lead of stub switch lead of 

 point switch) 



A stake is usually driven at Z, midway between the inner 

 rails and midway between the points N and N', and the turn- 

 out curves are continued to this point. This is more accurate 

 than to attempt to determine the point of reversal by the use 

 of the central angle M. 



Another Form of Cross-Over Between Two Parallel Straight 

 Tracks. A second form of cross-over is shown in Fig. 10. 

 In this form, the ends of the two equal turnouts are connected 

 by a straight track KTK'T'. The cross-over with a reversed 

 curve, Fig. 9, is much shorter than this straight-track cross- 

 over, and thus requires less length of track and occupies less 

 room. The straight-track form is, however, to be preferred; 

 it is less wearing on the rolling stock because it gives the wheel 

 trucks a better opportunity to adjust themselves to the reversion 

 of curvature. 



