The transverse slope added to lessen the influence of centrifugal force is known as superelevation.
It reduces the tendency of vehicles to turn sideways and slide sideways by extending the outer edge of the pavement with respect to the inner edge,
Superelevation and side friction are two aspects that contribute to the stabilization of a turning vehicle, the symbol for overgrowth is “e”.
The edge of the highway so that the outer edge of the pavement is higher than the inner edge is called superelevation.
In this article you’ll learn:
- What is superelevation?
- Purpose of superelevation.
- Methods of superelevation.
- Merits and Demerits of superelevation.
- Lots more.
So, if you’re ready to go with superelevation this article is for you.
Let’s get started!
What is Superelevation?
Superelevation is a method of constructing infrastructure in roadway curves in which the outer border of the pavement is increased above the inner margin.
It is a constituent of the vertical alignment or “profile” of a road viewed in cross-section; it is an essential protective aspect in the design requirements of any road with bends.
A superelevated road must be purposefully designed. Its construction necessitates the purchase of heavy machinery, substantial supplies, and a large labor force.
Superelevation is sometimes called “cant” or “banking,” as in a racing speedway’s banked track.
Purpose of Superelevation:
- The use of superelevation allows the vehicle to move more safely and faster than turns, rather than being allowed.
- Side friction between the tires and the road surface also works to neutralize the external pull of the vehicle.
- Side friction is reduced when there is water, snow, or ice on the road or when the tires are badly damaged.
- The maximum height for a piece of highway is determined by the weather conditions, the type of terrain, and the type of development.
Methods of Superelevation:
1. Elimination of The Crown of The Cambered Section:
The outside portion of the camber is slowly reduced using this procedure. There are two ways to accomplish this.
The outer side of the camber is rotated about the crest at the needed rate until the surface will be in the same plane as the inner corner in the first attempt.
The crown is gradually moved outwards in the second procedure. This approach is not commonly used.
2. Pavement Rotation for full Superelevation:
At this step, superelevation is gradually delivered throughout the whole width of the carriageway, such that the requisite superelevation is accessible at the start of the circular bend. The many methods used to achieve superelevation are as follows:
A. Circular Pavement Around the Centre Line:
In this manner, the road surface is rotated about the inner side, expanding the center and outside corner.
The center line’s level is kept constant.
This technique is extensively utilized.
B. Circular Pavement Around the Inner Edge:
In this manner, the road surface is twisted about the inner edge, expanding the center and outside edge.
C. Circular Pavement Around the Outside Edge:
The road surface is spun around the outside edge, lowering the center and inner edge.
Analysis of Superelevation:
Let, W = Weight of the vehicle,
v = Speed of the vehicle in m/sec,
g = Acceleration due to gravity in m/sec²,
f = Coefficient of friction,
e = rate of superelevation (tanθ),
F = Frictional force resistance due to centrifugal force,
P = Centrifugal force.
Now, P = Wv²/gR
For equilibrium, resolving the forces parallel to the inclined plane, are
P Cosθ = W Sinθ + F
Or, P Cosθ = W Sinθ + f(W Cosθ + P Sinθ)
After putting the value of P(P = Wv²/gR) we get,
Wv² Cosθ / gR = W Sinθ + f(W Cosθ + Wv² Sinθ / gR)
Or, v² Cosθ / gR = Sinθ + f(Cosθ + v² Sinθ / gR)
Now, both sides are divided by Cosθ, after that, we get the following equation:
v² / gR = tanθ + f(1 + v² tanθ / gR)
Or, v² / gR = tanθ + f + fv² tanθ / gR
The word fv2 tan / gR is too tiny and may be ignored.
v² / gR = tanθ + f
Or, v² / gR = e + f ………… (1)
If the vehicle’s speed is reported as V km/h, then
v = V1000 / 6060 m/sec Alternatively, v = 0.278V
The equation (1) therefore becomes (0.278V)2 / 9.81 R = e + f.
Or, e + f = V² / 127R.
Superelevation Equilibrium Formula:
If we use e = V2 / 127R, the value of ‘f’ will be 0, and the lateral friction will be ignored. This is referred to as equilibrium superelevation.
V2 / 127R = equilibrium superelevation (e).
IRC Design Calculation for Superelevation
According to the I.R.C., superelevation is computed at three-fourths of the design speed.
e = (0.75V) ² / 127R. Or, e = V² / 225R.
Maximum height limit:
According to IRC, the maximum elevation is 7% in snow-covered areas. Snow not restricted – 10%
Minimum high height limit:
Camber or Cross Slope = Minimum Elevation Camber: A slope that allows rainwater to flow rapidly in a horizontal direction is called camber or cross slope. It also prevents the car from slipping and falling.
What is the process of superelevation?
Superelevation interacts with many physical factors to assist vehicles to maintain speed and ride on the road safely through a curve.
The need for superelevation on a highway is governed by a complex combination of centrifugal and centripetal force, friction, inertia, weight, and velocity or speed.
Forces acting on Superelevation:
That sensation of approaching a curve and being pushed to one side? That is the centripetal force, the lateral force that enables a body to move in a circular motion.
You can generate centripetal force by tying the end of a line to a tennis ball and whirling it around you.
As a vehicle moves through a curve, the centripetal force pulls it toward the inside edge of the pavement.
It may appear that you are falling, tilting, or both.
It is the inverse of centrifugal force, which pulls you away from the centre of your automobile and toward the outside edge as it turns (and also pushes you into your seat).
A superelevated bend in a road balance these two forces, as well as many others that act in opposite directions.
Newton’s Law of Inertia states that anybody traveling in a straight path will continue to move in the same direction until it is impacted by an unbalanced force or anything that alters the direction of its motion.
In this case, the “subject” is a curve — or, more accurately, a driver’s decision to turn the steering wheel and change the vehicle’s course.
However, traction, or friction, is required to adjust inertia and safely change direction. Friction is the resistance created between your car’s rubber tires and the road surface.
Its function is to slow down the vehicle by keeping it in constant contact with the road (which also helps prevent it from sliding or skidding).
The weight of a vehicle can have an impact on its speed.
Heavier cars often apply more pressure to the road surface, resulting in stronger traction than lighter ones.
Speed or velocity is another component that, when combined with wetness, can help to reduce road friction.
This action in response is notably noticeable on raised highway bridges, as it is on most bridges, where cold air may condense moisture and transform it into ice.
Factors Affecting the Need for Superelevation:
- The curved form is an important aspect to determine how much elevation is required.
- The rate at which a vehicle moves across space.
- A vehicle design curve also affects the design of the superelevation.
- The geology and topography of the area where the curve is being constructed.
- The same type of pavement should also be considered.
- Rougher roads, where automobiles are more inclined to travel slowly, would need less superelevation.
- The size of the concerned vehicle ex. trucks, RVs, big construction trucks, and other vehicles with high centres of gravity are more prone to overturn or roll over on bends with insufficient superelevation.
What happens if superelevation is not used?
Superelevation is an important consideration in route design and the curves should be taken more carefully for safety.
Skidding can occur when friction fails to adjust for the curve’s forward velocity and centrifugal force.
That is why there are railings on highway ramps and high mountain paths and warning signs of impending turns, most of the time maximum speed is advised.
There is also a warning sign depicting a vehicle falling off two wheels due to high speed.
Larger vehicles, as mentioned earlier, are more likely to collide and overturn due to their high center of gravity.
If they try to navigate too early on a curved path without a bank, they are responsible for turning to their side.
Another consequence of inadequate overcrowding is road damage due to inadequately distributed loads, resulting in increased costs for repairing curved sections of highways.
Advantages of Superelevation:
- The super elevation is supplied to boost the vehicle’s speed.
- When speeding vehicles cross a horizontal curve, their stability increases, and foot tension decreases.
- Pits are likely to form on the outer boundary of the road when there is no additional height on the road around the turn.
- The Indian Road Congress (IRC) has set the maximum value of Super Elevation as one out of fifteen.
Disadvantages of Superelevation:
- Extra building costs due to high engineering, geological and concrete work.
- It can be complex, resulting in loss of vehicle control or instability.
- Excessive maintenance is due to increased maintenance of the tire. This increases the cost.
- More space is required for the construction project.
- Increases the weight of the vehicle, which increases the traction force on the base course by up to 20%
Also read: Types of Pavement | Sight Distance | Types of Bridges | Curb and Gutter
The superelevation allows drivers to safely and comfortably navigate the curve at normal speeds.
By elevating the outer edge of the pavement compared to the inner edge and forming a transverse slope over the whole length of the horizontal curve, it minimises the tendency of the vehicle to overturn or skid.