Determine the minimum length of a sag vertical curve if the grades are –4% and +2%. Design speed is 70 mi/h. State assumptions used. Consider the following criteria: stopping sight distance, comfort, and general appearance.
What will be an ideal response?
Assumptions used include: perception-reaction time is 2.5 seconds, deceleration
rate is 11.2 ft/sec2, and the case is sight distance is less than the length of the
curve.
For the sight distance criterion:
Determine required stopping sight distance using Equation 3.27:
Since S
For the comfort criterion, use Equation 15.10:
For the general appearance criterion, use Equation 15.11:
L = 100 A = (100)(6) = 600 ft
Therefore, for the given design conditions, the minimum length of the curve is
1,179 ft.
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