A Comprehensive Guide to Superelevation in Roads

What Is Superelevation in Road Construction?

The designer creates a transverse inclination in designing the cross-section of the pavement on a horizontally curved road, known as superelevation.

Superelevation plays an important role in road construction to prevent vehicles from overturning on a horizontal turn. Superelevation is essential for the safe driving of vehicles on curved sections of roads.

It helps fast-moving vehicles to move safely due to superelevation from the curved part of the stable roads. Superelevation is also commonly referred to as banking or Kent.

The superelevation of roads is given on the horizontally curved part of the road. In which inclination is kept keeping in view the outer edge of the road pavement from the inner edge.

How to Provide Superelevation in Road

1. When the vehicle goes from a straight road to a curved road, centrifugal force is applied to the vehicle. Superelevation is given on such curved roads to resist the impact of centrifugal force and drive the vehicle safely.
2. Preoperation prevents the vehicle from overturning off the road. As a result, the number of accidents is reduced.
3. Such supremacy helps divert rainwater to the side of roads. Therefore, there is no need to provide camber on curved roads with superelevation.
4. It helps keep the speed of your vehicle stable with safe driving on curved roads.
5. It also helps the vehicles to keep their position on the roads on their right side. And in this way, an accident can be prevented with vehicles going in opposite directions.
6. The main purpose of superelevation is to resist the influence of centrifugal force applied on a moving vehicle.

Maximum Superelevation

According to the IRC, it is recommended to keep the maximum ratio of superelevation in rolling and plain terrain at 1 in 15 or 4 degrees.

Up to a maximum of 10% provision has been made by the IRC on mountain roads not covered by snow.

What Is Maximum Superelevation in Road?

The limit of minimum superelevation is equal to the amount of camber placed on the road. It is an especially large radius for horizontal curvature that can be kept higher for 2-4% drainage purposes.

Superelevation Formula

The following formula is provided by calculating the superelevation on the road.

e + f = (V² / 127 R)

where,

R = 0.036 V²

e = rate of superelevation,

f = design coefficient of lateral friction

g = acceleration due to gravity

R = radius of the curve

Advantage of Superelevation

 

1. Superelevation is given on such curved roads to resist the impact of centrifugal force and drive the vehicle safely.
2. Such supremacy helps divert rainwater to the side of roads. Therefore, there is no need to provide camber on curved roads with superelevation.
3. Due to superelevation, the vehicle can be driven safely on the road.
4. On curved roads, superelevation is provided on curved roads to prevent the vehicle from overturning.
5. Superelevation provides more or less load friction on the wheels of the vehicle and therefore feels the same tensile force on the foundation. The result is an economy in the cost of maintaining the cost of wheel tires and roads.

Design of Superelevation

Calculate superelevation (E) for 75% design speed [0.75V] in road. and assume that the value of lateral friction is zero.

Step 1:

As a practical situation, it is suggested to take the developed side friction (F = 0) and calculate the superelevation to fully resist the centrifugal force at 75% of the design speed (V).

Speed design Calculate the required 75% design speed and assume zero value of friction,

super elevation formula,

e + f = (V² / 127 R)

where, f = 0, V = 0.75V

e + f = [V²]/127R

∴ e + 0 = [0.75V]²/127R

∴ e = V² / 225R.

Note: The value of E should not exceed 0.07.

Step – 2

Let us proceed to the next step as assume e = e_max = 0.07.

Let us now find the value of friction (f) for the known value of the e_max value.

Super Elevation = e_max + f = [V²]/127R

∴ 0.07 + f = [V²]/127R

∴ f_cal   = [V²/127R] – 0.07.

If f_cal  > f_max (0.15)

Then e = 0.07 is safe.

Step – 3

The next step is calculate the value of Restricted Speed (V_a)

where, V = V_a

Super Elevation = e + f = [V²]/127R

∴ 0.07 + 0.15 = (V_a)²/127R

∴ V = [127R(0.22)]^1/2.

Method of Providing Superelevation to the Roads

The introduction of superelevation over the horizontal curve of the road is an important part of road construction. The two methods mentioned below provide gate superelevation.

1. Elimination of the crown-cambered section
2. Rotation of pavement

1. Elimination of the crown-cambered section.

In this method, the outer part of the camber in the road is gradually reduced. This can be done in two ways.

1.1. In the First Method

In the first method, the outer part of the camber is rotated about the crown at the desired rate. Which falls on the same plane in the inner half of the surface of the road.

1.2. In the Second Method

In the second method, the crown is gradually shifted from the outside of the road to the outside of the camber. This method is not generally adopted.

2. Rotation of pavement

At this stage, a gradual overlap is provided over the width of the carriageway so that the required superelevation is achieved at the beginning of the circular curve. This method involves different methods to achieve superelevation.

2.1. Pavement Moving Around the Centerline

In this method, the inner surface is gradually lowered by turning the road surface above the midline of the carriage van. And thus the upper edge increases. But care is taken to keep the level of the centerline constant.

2.2. Revolving Pavement on the Inner Edge

In this method, the carriageway of the road surface is rotated around the inner edge of the way. Which extends to the middle surface and outer edge.

2.3. Revolving Pavement on the Outer Edge

In this method, the road surface carriage is rotated around the outer edge of the way which reduces the middle and inner edge.