. Railroad construction. Theory and practice . Fig. 210. AN represents an actual uniform grade consisting of tangentsand curves, the ^Sdrtual grade on curves at BC and DE maybe represented by BC and DE. If BC and DE are very long,or if a stop becomes necessary on the curve, then the full dis-advantage of the curve becomes developed. If the whole grademay be operated without stoppage, then, as elaborated furtherin the next chapter, the w^hole grade may be operated as if equalto the average grade, AF, which is better than BC, althoughmuch worse than AN. The process of ^compensation con-sists in
. Railroad construction. Theory and practice . Fig. 210. AN represents an actual uniform grade consisting of tangentsand curves, the ^Sdrtual grade on curves at BC and DE maybe represented by BC and DE. If BC and DE are very long,or if a stop becomes necessary on the curve, then the full dis-advantage of the curve becomes developed. If the whole grademay be operated without stoppage, then, as elaborated furtherin the next chapter, the w^hole grade may be operated as if equalto the average grade, AF, which is better than BC, althoughmuch worse than AN. The process of ^compensation con-sists in reducing the grade on every curve by such an amountthat the actual resistance on each curve, due to both curvatureand grade, shall precisely equal the resistance on the practical effect of such reduction is that the Sirtual gradeis kept constant, while the nominal grade fluctuates. One effect of this is that (see Fig. 211) instead of accomplish-. FiG. 211. ing the vertical rise from A to G (, HG) in the horizontaldistance AH, it requires the horizontal distance AK. Such anaddition to the horizontal distance can usually be obtained byproper development, and it should always be done on a ruling § 428. CURVATURE. 457 grade. Of course it is possible that it will cost more to accom-plish this than it is worth, but the engineer should be sure ofthis before allowing this virtual increase of the grade. European engineers early realized the significance of unre-duced curvature and the folly of laying out a uniform ruUnggrade regardless of the curvature encountered. Curve compen-sation is now quite generally allowed for in this country, butthousands of miles have been laid out without any compensa-tion. A very common limitation of curvature and grade hasbeen the alliterative figures 6° curvature and 60 feet per mileof grade, either singly or in combination. Assuming that theresistance on a 6° curve is equiA^alent to a grade
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