Crest vertical curves are curves that connect inclined sections of roadway, forming a crest, and they are relatively easy to design. The principal control in the design of crest vertical curves is to ensure that minimum stopping sight distance (SSD) is available throughout the verticl curve. An appropriate length for the curve is required that will accommodate the correct sight distance.
Crest Vertical Curve Design : calculated using the formula stated in reference [ 2], pp. 60.
For SSD < L US Customary Metric
For SSD > L US Customary Metric
SSD = stopping sight distance in ft (m),
= minimum length of vertical curve in ft (m), and
A = absolute value of the differences in grades () expressed as a percentage.
The general form of the parabolic equation, as applied to vertical curves, is
y = roadway elevation at distance x from the beginning of the vertical curve in ft (m)
x = distance from the beginning of the vertical curve in stations or ft (m)
c = elevation of the point of vertical curvature (PVC) in ft (m),
= initial roadway grade in percent, it is as referred as the initial tangent grade
= final roadway (tangent) grade in percent.