The inward transverse inclination provided to cross section of carriage way at horizontal curved portion of the road is called as Super Elevation. It is also referred as to Cant or Banking.
- To counteract the effect of centrifugal force acting on moving vehicle.
- To help a fast moving vehicles to negotiate a curved path Without overturning and skidding.
- To ensure smooth and safe movements of passengers and goods on the road.
- To prevent damaging effect on the road surface due to improper distribution of load.
- The maintenance cost of road on curve is reduced.
How to Calculate Super Elevation ?
For Example : Calculate the super elevation required for road of 7 m wide on a curve of 250 m radius for permissible speed of 80 kmph. Let the coefficient of friction be 0.15.
The formula for calculating is given below :
e = Super elevation.
f =coefficient of friction.
v = speed in kmph.
R = Radius of the curve in metre.
Putting all the values in the formula we get,
∴ e = 0.201 – 0.15 = 0.051 per meter of carriage way.
∴ Super elevation = 0.051 * 7 = 0.357 m or 35.7 cm above the inner edge of the road.
Minimum and Maximum Super Elevation.
- If the elevation is less than the value of camber of a road, it should be kept equal to the camber of the road for drainage purpose.
- In case of flat curves with large radius, the super elevation will be negligible, as the centrifugal force which will be developed will be very small. Under such condition, the normal camber may be retained also on the curve.
- But, such a practice will result into negative elevation on the outer half of the road.
- The centrifugal force combined with negative elevation will be less than allowable friction coefficient.
- Below shows the recommended radius of horizontal curves beyond which normal cambered section may be maintained without the provision of super-elevation.
- For mixed traffic pattern where there is fast moving vehicles as well as slow moving vehicles like bullock cart.
- High value of super elevation is in convenience. Hence the maximum value of elevation in plain and ruling terrains and in snow bound areas has been fixed by IRC as 6.7 percent i.e. 1 in 15.
- However for hill roads not bound by snow, a maximum limit of super elevation is upto 10% i.e. 1 in 10 has been recommended by the IRC values.
- Thus the maximum allowable value of (e + f) works out to (0.067 + 0.15) = 0.217.
- From this the minimum value of radius R given to a curve when the speed is known can be obtained.
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