Module 3: Geometric design of highways

Lecture 18 Vertical alignment II

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Valley curve

Valley curve or sag curves are vertical curves with convexity downwards. They are formed when two gradients meet as illustrated in figure  1 in any of the following four ways:

Figure 1: Types of valley curve

1. when a descending gradient meets another descending gradient [figure 1a].
2. when a descending gradient meets a flat gradient [figure 1b].
3. when a descending gradient meets an ascending gradient [figure 1c].
4. when an ascending gradient meets another ascending gradient [figure 1d].