where:
V = vehicle speed in miles per hour (mph)
R = radius of curve in feet
e = rate of roadway superelevaion in feet per foot
f = side friction factor with value depending on speed as follows:
| If the speed is: 35 mph or greater between 20 and 35 mph 20 mph or less |
Then the side friction factor is: 0.15 0.18 0.31 |