The following excerpt about the combination of horizontal and vertical alignments in roadway design was taken from page 297 of the 1990 edition of AASHTO's A Policy on Geometric Design of Highways and Streets.

Coordination of horizontal alignment and profile should not be left to chance but should begin with preliminary design, during which stage adjustments can readily be made. Although a specific order of study for all highways cannot be stated, a general procedure applicable to most facilities can be outlined.

The designer should use working drawings of a size, scale and arrangement so that he can study long, continuous stretches of highway in both plan and profile and visualize the whole in three dimensions. Working drawings should be of sufficiently small scale, generally 1 inch = 100 feet or 1 inch = 200 feet with the profile plotted jointly with the plan. A continuous roll of plan-profile paper usually is suitable for this purpose.

After study of the horizontal alignment and profile in preliminary form, adjustments in each, or both, can be made jointly to obtain the desired coordination. At this stage the designer should not be concerned with line calculations other than known major controls. The study should be made largely on the basis of a graphical analysis...