Civil Engineering PE

Answer: C - The stopping sight distance (SSD) for a roadway with a speed of 35 mph on a downgrade of 9% is 287 feet.

Solution: Use the SSD on grade equation (US Customary units)

d = 1.47Vt + V²/30((a/32.2) - G)

Where, t = 2.5 seconds

a = 11.2 feet/second²

V = 35 mph

G = - 0.09

d = 1.47 (35) (2.5) + (35)²/30((11.2/32)-0.09)

= 128.6 + 158.4

= 287 feet