All grade lines between adjacent points at which grade elevations are given in this article shall be straight, except that at points intermediate between street intersections, and at all other points which the rate of grade changes, vertical curves shall be inserted. Each vertical curve shall be a parabolic arc, tangent to the intersecting straight lines at points equidistant from the vertex.

Except where otherwise provided, the length of all vertical curves shall be fixed at the time the street is improved, and the length of each particular vertical curve shall be determined by the engineer, which in his judgment can be used to the best advantage. [Code 1975 § 8-1.0602.]