If the sight distance (S) is equal to the length of the vertical-curve (2l) joining two grades g1% and – g2%, the height of the apex will be

An alternative method to determining the minimum length of a sag vertical curve (L) is to multiply the rate of vertical curvature (K) for the design speed of the roadway by the algebraic difference in the tangent grades (A) in percent (L=K*A).