RAILROAD CURVES 



165 



curve at this point in the same manner as if this point were 

 the P. C. of the curve. 



Tangent and Chord Deflections. Let AB, Fig. 6, be a 

 tangent joining the curve BCEH at B. If the tangent AB 

 is prolonged to D, the perpendicular distance DC from the 

 tangent to the curve is called a tangent deflection. If the chord 

 BC is prolonged to the point G, so that CG = CE, the distance 



GE is called a chord deflection. If the radius R of the curve 

 and the length of the chord c are known, the tangent deflec- 

 tion / can be determined by the formula 



This formula can be used for any length of chord or radius. 



c 2 



If CE = BC, the chord deflection = 2 /= . For this condition, 



jR 



the table of radii and deflections gives the chord deflection 

 and tangent deflection for 100-ft. chords and for degrees of 

 curvature varying by intervals of 5' and 10' from 5' to 20. 



