### Superelevation Formula

Superelevation Formula

The superelevation is provided on the road by the following formula

e + f = (V2 / 127 R)

R = 0.036 V2

Where,

e = rate of super elevation

f = design coefficient of lateral friction= 0.15

g = acceleration due to gravity= 9.81 m/s2

R = radius of the curve

By using this formula the angle of superelevation is also determined.

Minimum and Maximum Superelevation in Roads

Superelevation which is provided on the road is less than the camber of a road then it should be equal to the camber of the road for proper drainage purposes.

In the case of heavily loaded vehicles having denser material, it is not possible to move this vehicle on the road with a high rate of superelevation.

The Center of gravity of the loaded vehicles is relatively high so it is not safe to move these vehicles from the curved portion of the road where high superelevation is provided.

In the case of flat curves with a larger radius, the superelevation will be negligible as the centrifugal force which will be developed is very less. In this condition, the normal camber may be retained also on the curve.

Hence, in order to avoid the danger of toppling of the loaded vehicles and ensure the safe movement of the vehicles on the curved portion of the road.

It is essential that there should be a limit of maximum allowable superelevation in the roads.

Indian Road Congress(IRC) has recommended the limit of maximum allowable superelevation in the roads for a plane and rolling terrains and snow bound areas is 7% taking mixed traffic into the consideration.

For Areas which are not bound by snow the maximum limit of the superelevation which is recommended by the Indian Road Congress is up to 10%.

IRC recommendation for radii beyond which Superelevation is not required.

 SRNO Design Speed in Kmph Radius in Meters of Camber 4% 3% 2.5% 2% 1.7% 1 20 50 60 70 90 100 2 25 70 90 110 140 150 3 30 100 130 160 200 240 4 35 140 180 220 270 320 5 40 180 240 280 350 420 6 50 280 370 450 550 650 7 65 470 620 750 950 1100 8 80 700 950 1100 1400 1700 9 100 1100 1500 1800 2200 2600
• Method of Providing Superelevation to the Roads

Superelevation plays an important role to counteract the centrifugal force which is acting on the vehicle moving from the horizontal curve of the road.

The attainment of superelevation in roads is done into two parts

• Elimination of the Crown and the cambered section

• Rotation of the pavement by attaining full superelevation

Elimination of the Crown and the Cambered Section

Method – 1.

In the first method, the outer half of the cross slope is rotated about the crown at the rate such that the surface of the road falls on the same plane and the elevation of the centerline is not varied.

The outer half of the cross slope is brought to the level rotating about the crown line at the start of the transition curve.

There is no point on the curve that will have a negative superelevation at the outer half of the pavement at the start of the transition curve.

Method – 2.

In the second method, the crown is gradually shifted by increasing the width of the inner half of the cross-section.

This method is not usually adopted as a portion of the outer half of the pavement which has increasing values of negative superelevation on to a portion of the outer half.

• Rotation of the pavement by attaining full Superelevation

In this method, the inner edge of the road is made the pivot point. The Crown, as well as the outer edge, are raised in such a way that the full amount of superelevation is achieved.

The disadvantage of this method is that the center of the pavement is raised and the entire pavement width and the outer shoulder are to be raised with respect to the inner edge by additional filling of the earth.