Fit a horizontal curve to a required external distance
An obstruction near the PI forces the curve to stay at least 65.00 ft out from the intersection point. The minimum radius is solved from the external distance, rounded to a design value, and stationed.
Apply· about 18 minutes by hand· 5 steps
Given
Two tangents intersect at a PI with a deflection angle Δ = 36°20′00″. Station of the PI = 96+14.50.
A masonry headwall stands on the bisector of the interior angle at the PI. Its face is 65.00 ft from the PI, measured along the bisector toward the outside of the curve.
The alignment must pass outside the headwall, so the midpoint of the curve must be at least 65.00 ft from the PI.
Design policy is to adopt a radius that is a multiple of 25 ft.
All distances are US survey feet.
Required
The minimum radius that satisfies the external-distance constraint.
The design radius adopted, and the external distance it actually gives.
The complete curve elements and the stations of the PC and PT for the adopted radius.
Work it through yourself before reading on - the solution below shows every step, so there is no way to skim it without giving the answer away.
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