Rate of Change of Grade Per Station

Highway engineers generally describe a vertical curve by stating its length and the rates of the adjacent tangent grades. Although this definitely establishes the curve it does not give a comprehensive idea of its sharpness. A curve in horizontal alinement is described by its angle of intersection, radius or degree of curve, length and tangent distances, and the bearings of the adjacent tangents. These data, especially the radius, convey a very definite picture of the sharpness of the circular curve. A vertical curve is part of a parabola, computed and laid out using horizontal and vertical measurements. Being a parabola, a vertical curve has no constant radius or degree of curve, which probably accounts for the lack of such a factor in its description.