Superelevation | Factors Affecting Super elevation Design | A Method of Providing Road Superelevation
One of the most important features in road construction is super elevation on horizontal curves. It is essential to provide super elevation on roads for the safe movement of vehicles on curved sections of roads. It allows fast-moving vehicles to travel safely on the curved portions of the roads.
When a driver approaches a curve, the road is frequently tilted or banked at an angle, which makes it easier to navigate the curve at a safe speed without skidding or tipping. This is superelevation in action.
On curved roads, superelevation assists drivers in maintaining both safety and optimal speed. Without superelevation, many vehicles, especially those traveling at high speeds or in slick or icy conditions, would slide or skid through curves or even topple over. Additionally, it enables traffic to maintain some speed when negotiating curves, avoiding prolonged slowdowns at each bend in the road.
What is Superelavation?
Super elevation is the inward transverse inclination provided to the carriageway cross-section at a horizontally curved portion of a road. Super elevation is also known as “cant” or “banking,” as in a racing speedway’s banked track.
A super elevation is provided on the road to counteract the effect of centrifugal force and to reduce the tendency of the vehicle to overturn or skid by raising the outer edge of the pavement with respect to the inner edge, resulting in a transverse slope along the length of the horizontal curve.
A super elevated road’s design must be precise. Its construction requires the investment of heavy machinery, extensive materials, and a large labor force. However, if done correctly, most people will not even notice it is there.
Purpose of providing Superelevation
- The primary goal of providing superelevation is to counteract the effect of centrifugal force acting on a moving vehicle.
- To help support a fast-moving vehicle in navigating a curved path without overturning or skidding.
- To ensure the safety of fast-moving traffic
- To avoid damaging the road surface due to improper load distribution.
Advantages of Superelavation
- It allows vehicles to travel at high speeds on curved paths as if they were straight paths, resulting in increased traffic volume.
- It provides more or less even load distribution on wheels, resulting in uniform stress on the foundation and less wear on wheel tires and springs, as well as savings in road maintenance costs.
- It also helps to keep vehicles on the proper side of the pavement, preventing collisions between vehicles traveling in opposite directions on a curved portion of the roadway.
- It provides drainage along the entire length of the road, toward the inside. As a result, there is no need for a side drain on the road’s outer edge.
Disadvantage of Superelevation
Additional Construction Costs
- Extra construction costs due to additional engineering and geological work, as well as concrete construction, are required for superelevation.
More space is required
- This will require additional space and may require additional construction space.
It can be difficult
- If not done correctly, it can result in the vehicle losing control or becoming unstable.
- This is caused by increased tire wear. It raises the cost of maintenance.
Also Read : Pavement Markings | Road Signs
Factors Affecting Superelevation Design
1. The curve’s shape
The shape of the road can also have an impact on the amount of superelevation required.
Although not every curve requires the same amount of superelevation, there are some fundamental principles that can be used to determine how much superelevation is required for a specific curve.
2. The design speed of the vehicle on the road
Additionally, the design of superelevation is influenced by the speed at which traffic passes through a curve.
For instance, a road curve for driving at slower speeds needs to be designed at a lower superelevation because the stopping distance would be greater.
3. Geology and topography
Superelavation design is also impacted by the topography of the area where the turn is being planned. In areas with heavy rocks, uneven ground, or hills, a greater amount would be required.
4. Road Friction and Materials Used in Road Construction
The material used in road construction will also have an impact on the amount of superelevation required.
In comparison to soft materials like asphalt, hard materials like concrete will demand more superelevation.
5. Vehicle operation
The amount of superelevation used in a turn is affected by the type of vehicle operating on the road and carrying a load.
Superelavation would be needed more when carrying a heavier load than when carrying a lighter one.
6. The allowable centrifugal ratio
The centrifugal ratio is a concept that applies when a vehicle is traveling at high speeds on a smooth, level surface of the road.
It is the maximum speed at which a vehicle can travel in one direction before beginning to rotate.
The superelavation needed on a specific curve will be expressed as “c” in relation to the centrifugal ratio, which is referred to as “C.”
A Method of Providing Road Superelevation
There are typically two methods used for superelevation.
- Elimination of the Cambered Section’s Crown
- Rotation of the pavement cross-section for maximum superelevation
A. Elimination of the Cambered Section’s Crown
In this method, the camber’s outer halves are gradually reduced. There are two ways to do this.
- In the first process, the outer half of the camber rotates around the crown only when it is desirable, just to align the surface with the inner portion.
- The second process involves a gradual outward shift of the crown. It is uncommon to employ this strategy.
B. Rotation of the pavement cross-section for maximum superelevation
1. Rotation About the Center Line
- It is preferred by the vast majority of artists. In this process, the middle line of the straight road surface is gradually rotated, depressing the inner edge while increasing the outer edge by half of the total superelevation.
- As a result, the earthwork is balanced, indicating that the amount of cutting and filling required in this process is equal.
- The disadvantage of this method is flooding, which is caused by lowering the inner edge below the general floor.
2. Rotation about the Inner Edge
- This method entails gradually turning the straight roadway around the inner edge while increasing the middle line and outer portion in accordance with the required slope.
- In this instance, the maximum amount of superelevation is applied to the outermost layers.
- This approach is preferred on very flat ground in heavy rainfall zones to immediately protect drainage issues. Because the path’s vertical orientation is altered, the increase in the centerline is regarded as a disadvantage in this process.
3. Rotation about the Outer Edge
- Using this method, the straight road surface is gradually rotated around the outer edge, depressing the middle line and the outer edge in accordance with the desired slope.
- The entire amount of superelevation relative to the outer edge depresses the inner edge. This technique is the same as the rotation around the inner side.