166 



RAILROAD CURVES 



When the two chords preceding the station considered are 



of unequal lengths, the chord deflection = , where c\ 



2 R 



is the length of the first chord and a the length of the second 

 chord preceding the station considered. When the tangent 

 deflection / is known, the chord deflection 



Special Values of Chord and Tangent Deflection. For a 



chord of 100 ft. preceded by one of the same length the chord 

 deflection for a 1 curve is 1.745; for a 2 curve, it is twice that 

 amount, or 3.49; and so on. The tangent deflection, being 

 half the chord deflection, will be .873 ft. for a 1 curve, 1.745 

 for a 2 curve, etc. The tangent deflection for a chord of any 

 length equals the tangent deflection for a chord of 100 ft. 

 multiplied by the square of the given chord expressed as the 

 decimal part of a chord of 100 ft. 



Application of Chord and Tangent Deflection. Let it be 

 required to restore center stakes on the 4 curve, Fig. 7, at 

 each full station. The points A and B determine the direc- 



ir *> 



FIG. 7 



tion of the tangent, the point B being the P. C., which is at 

 Station 8+25. For a 4 curve the regular chord deflection 

 for 100 ft. is 4X1.745 = 6.98 ft., and the tangent deflection is 

 3.49 ft. The distance from P. C. to the next full station is 

 75 ft.; hence, the tangent deflection CF=.75 2 X 3.49 = 1.96 ft. 

 The point F is found by first measuring 75 ft. from JB, thus 

 locating the point C in the line AB prolonged, then from C 

 measuring CF=1.96 ft., at right angles to BC\ the point F 



