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 The topics discussed under vertical alignment can be divided into two categories: the design of highway sections that have ascending or descending grades, and the design of vertical curves that connect these segments of ascending and descending grades. Grade is a measure of the inclination, or slope, of the roadway. It is defined as the rise over the run. In other words, a 10% grade simply means that the elevation of the roadway increases by 10 feet for every 100 feet of horizontal distance. The issues that surround the design of inclined roadway sections revolve around safety and level of service. Vertical curves, however, are slightly more complicated. The best feature of the vertical curve, in its purest form, is that it doesn't require any changes in the roadway cross-section. In this respect, vertical curves are easier to design than horizontal curves. On the other hand, vertical curves have a parabolic shape instead of the simple circular shape of the pure horizontal curve. Because this makes certain calculations more involved, we will spend more time explaining issues that we would otherwise leave for surveying texts. The general discussion regarding vertical curves covers the geometry of simple vertical curves. The discussions pertaining to sag and crest vertical curves include more specific information related to the design of these curves.
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