What is Superelevation? Purpose of providing Superelevation in roads…..
What is Superelevation?
When a vehicle crosses a curved path, it is subjected to an outward force known as Centrifugal Force. To oppose this force, the outer edge of the road is raised above the inner edge. This is known as Superelevation or Banking or Cant. It is the transverse slope provided to neutralize the effect of Centrifugal Force and reduce the tendency of vehicles to overturn or to skid.
Advantages of providing super-elevation →
- Decrease the intensity of stresses on the foundation.
- Increase the stability of the fast-moving vehicles, when they cross a horizontal curve.
- Achieve a higher speed of vehicles.
Superelevation shouldn’t be less than the camber. To avoid the risk of the overturning of a bullock cart on the curves, the Indian Road Congress (I.R.C.) has prescribed the maximum value of superelevation as 1 in 15.
V = Speed of the vehicle km/h
R = Radius of curvature in meters
e = Rate of superelevation
f = Lateral friction coefficient = 0.15
When the coefficient of friction is neglected (i.e. f=0), then the superelevation is
It is suggested that superelevation should be provided to fully oppose the centrifugal force due to 75% of the design speed (V) by neglecting lateral friction developed. Therefore, the maximum rate of superelevation is
Disadvantages of providing super-elevation →
- This method has a drawback in that the surface drainage will not be proper at the outer half, during a short stretch of the road with a cross slope less than camber.
- The majority of permanent way materials are specific ones, therefore their availability is limited or non-existing.
- Lack of standard for the design of dual tracks.
- Track construction machines are to be fit for non-standard structural solutions.
- Traffic turning right has to travel a little extra distance.