RAILROAD LOCATION 



231 



CV and VD. The projections RT and TS of the distances 

 VC and VD from the vertex to the points at which the ver- 

 tical curve begins and 

 ends are always chosen 

 equal. If K is the 

 middle point of the 

 straight line CD, the 

 vertical curve is always 

 so chosen that it will fb) 



bisect VK; that is, so p IG . 2 



that VM = MK. 



Let E be the elevation of C, Fig. 3, E r that of D, and H that 

 of V, so that E = RC, E' = SD, and H = FZ\ Then, 



The distance VM is called the correction in ^rade at the 

 point V. 



Vertical curves are always made parabolic. It is a prop- 

 erty of the parabola that the correction in grade am at any 

 point a is given by the equation, 



VMX ( 



The distance CV=VD is always made a whole number 

 of stations; and, to simplify the work, the grade stakes a, b, c. 



J>at>nn Plane 



FIG. 3 



etc., are so set that they divide the distance CV into a num- 

 ber of equal parts. The corrections in grade at points a', l/ t 



