When two vertical gradients meet, it is necessary to provide a vertical curve. Two types of vertical curves are used:
(a) Summit curve, where the point of intersection of the two gradients is above the road. (Figure 9)
(b) Valley curve, where the point of intersection of the two gradients is below the road. (Figure 10)
The length of the vertical curve is determined from considerations of
(a) Availability of sight distance
(b) Headlight sight distance, when the driver has to apply brake to stop the vehicle if the headlight of the opposing vehicle blinds him, and
(c) Rider comfort.
Figure: Summit Curve