Question

If the stopping sight distance required to avoid colliding with a fallen boulder on a mountain pass is 800 feet, what is the likely grade of the mountainous segment of roadway. Assume a perception-reaction time of 2.5 seconds, a design speed of 65 miles per hour, and an a/g value equal to 0.35. [Use Practical Stopping Distance]

Answer 1

Answer:

Grade is 10.32%

Explanation:

Given data:

stopping side distance is 800ft

t = 2.5 sec

design speed v = 65 miles/hr

a/g value is 0.35

stopping side distance is SSD

$SSD = 1.47 vt + \frac{v^2}{30(a/g - G}$

plugging all value for G

$800 = 1.47 \times 65\times 2.4 + \frac{65^2}{30(0.35 -G)}$

$800 - 229.32 = \frac{65^2}{30(0.35 -G)}$

$570.68 = \frac{65^2}{30(0.35 -G)}$

G = 0.1032

Grade is 10.32%