Two main forces act on a super elevated curve: the overbalance, a static or dynamic condition which the resultant force is less than equilibrium speed.
And the unbalance, on the opposite direction of the first, and occurs due to a dynamic condition which the resultant force exceeds equilibrium speed.
To determine the unbalance the following formula can be used:
Vmax = √ ((Ea + U)/.0007D)
where: Vmax = Velocity of train (maximum allowed speed in MPH)
Ea = Actual Elevation (inches)
U = Unbalance (inches)
D = Degree of Curvature (decimal degrees)