Civil Engineering PE

Answer: C - The minimum safe radius of a horizontal curve for a two-lane rural highway with a speed limit of 60 miles per hour (mph) and an 8% rate of superelevation is 1,200 feet.

Solution: Use AASHTO Equation

R_min = V²/15(0.01e_max + f_max)

Where V = 60 mph

f_max = 8%

R_min = 60²/15((0.01) (8) + 0.12))

= 1,200 feet