Sag Vertical Curves
If a stopping sight distance of 400 ft. is to be maintained on a sag
vertical curve with tangent grades of -3% and 0%, what should the length of the curve be?
Assume a headlight beam upward divergence angle of 1°.
[Solution Shown Below]
Solution
Since we know everything that we need to know to solve this problem, we'll jump
straight into the equations.
If S > L then
If S < L then (invalid because L < S)
Where:
L = Curve length (ft)
S = Sight distance, 400 f.
B = Beam upward divergence, 1°
H = Height of the headlights, 2 ft (assumed as 2 ft)
A = Change in grade, 3% (|G2-G1| as a percent)
Solving the equations above results in a curve length of 201 feet. You can find
the elevation of any point along the curve once you have the curve length. See the
crest vertical curve example problem.
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