Civil Engineering PE

Answer: A - the rate of superelevation required for a horizontal curve on a 45 mile per hour (mph) two-lane rural highway with a minimum safe radius of 710.5 feet is 4%.

Solution: Use the Minimum Radius equation using e_max and f_max

R_min = V² / 15(0.01e_max + f_max)

Where V = 45 mph

R_min = 710.5 feet

f_max = 0.15

710.5 = (45)² / 15(0.01e_max + 0.15)

710.5 = 2025 / (0.15e_max + 2.25)

e_max = 4%