13 Key Advantage and Disadvantages of Superelevation | Definitions & Function Of Superelevation
What is Superelevation? | Advantage and Disadvantages of Superelevation | Function of Superelevation | Minimum and Maximum Superelevation
What is Superelevation?
Superelevation is a special design of a road that allows drivers to safely exit the road at high speeds. The design of the incline and curb radius on a superelevated road allows for drivers to adequately take a turn without skidding and crashing.
Safety is the number one priority when designing roads. Superelevation is a key factor in ensuring a safe driving experience.
The word superelevation is a word used to describe a feature of most modern roadways. It can also be called crowning or camber.
One aspect of the superelevation is to allow for a better flow of traffic. This occurs by reducing the difference between the elevation of the center of the lane and the elevation of the edge of the lane
Federal Highway Administration has given maximum and minimum superelevation that is used in the highways designed and built in the United States.
Maximum Superelevation is defined as “the maximum slope of a highway curve that can be safely traversed without inducing undue sway or instability in passenger cars” (FHWA).
The current standard set by engineers has been to use five degrees as this maximum superelevation, which was decided on because any steeper than that would cause drivers to lose control of their vehicles if they were traveling at high speeds.
The default values are 2% for the inside lane of a 2-lane highway, and 4% for the outside lane. Each lane is 8 feet wide, so the amount of superelevation is about an inch.
Function of Superelevation
The function of superelevation is to allow vehicles to maintain a safe and stable trajectory. Without it, the vehicle will either understeer or oversteer.
Different speeds and road characteristics call for different levels of superelevation.
Having the right amount of superelevation on your roadway is important for safety. Roads with excessive superelevation can create adverse effects such as severe tire wear, stress to suspension, and driver discomfort.
The Super-Elevation is a concept that is often used in highways and intersections to help drivers feel more confident and comfortable that they are driving on a flat surface
The superelevation formula is a mathematical equation that calculates the degree of curve in a roadway.
The results are used to determine how much it will cost to pave the road and how long it will take to complete.
The superelevation is provided on the road by the following formula
e + f = (V2 / 127 R), R = 0.036 V2
- 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
To calculate the rate of change in superelevation divide the difference between normal crown and full super by the transition length.
The rate of change is the same as for the transition at the curve’s beginning.
Factor Affecting the Design of Superelevation
1. Shape of the curve
The shape of the road curve can also be an important factor in determining the amount of superelevation that is needed.
Not every curve requires the same amount of superelevation, however, there are some basic principles that can be applied to know what superelevation will be needed for a particular curve.
2. The vehicle’s design speed on the road:
The speed at which traffic travels through a curve has an impact on the design of superelevation as well.
For instance, a road curve will need to be designed at a lower superelevation for driving at slower speeds, as the stopping distance would be longer.
3. Geology and Topography
The type of topography of the area where the turn is being designed for also has an impact on design of superelevation. A greater amount would be required in areas where there are heavy rocks and uneven ground or hills.
4. Road Friction & Material used in the construction of the road
The road design material will also have an effect on the amount of superelevation that is required.
Hard materials such as concrete will require a greater amount of superelevation as compared to soft materials such as asphalt.
5. Vehicle operation
The type of vehicle operating on the road which is carrying a load will have an impact on the amount of superelevation that is used in a turn.
A heavier load would require more superelevation than one carrying lighter loads.
6. Centrifugal ratio that is permissible
The centrifugal ratio is a concept that applies to the situation where a vehicle is traveling at high speeds on an area of the road with a smooth, level surface.
It refers to the maximum speed at which the vehicle can travel in one direction before it starts to rotate.
The centrifugal ratio is referred to as “C” and the superelevation that is required on a particular curve will be expressed as “c” in relation to this ratio.
Advantage and Disadvantages of Superelevation
Advantage of Superelevation
1. It reduces tire stress
Superelevations are usually employed to keep excessive wear on tires and suspension components away from the driver’s eyes. They also reduce aerodynamic drag that increases fuel consumption.
2. It increases vehicle speed in curves
The slower the speed of the vehicle, the greater the superelevation required. This is a key to increasing driving speed as you approach bends in the road.
The combination of sharper bends and the increasing superelevation forces drivers to increase their speed, creating a flow of traffic that is more levelled out than if cones and signs were used.
3. It allows for better drainage
Maintaining proper drainage in road designs is incredibly important. Superelevation can help with this task as well, as it assists in preventing water from pooling in the center of the road.
4. It allows for better visibility
Trees and other obstacles can make it more difficult for drivers to see oncoming traffic in rural areas.
Superelevations allow drivers to better see these obstacles when they are driving at high speeds, thereby reducing the chances of an accident occurring in these areas.
5. It reduces accidents
According to section 3B of Hun, et. al. the increased traffic and higher speeds caused by the increased superelevation makes for a safer driving experience.
This also increases the amount of traffic that is on the road, which lowers congestion and allows for better flow of traffic, which ultimately makes for a safer road design.
6. The S curve type curve is adequately handled by superelevating
S curve may be one of the most technically demanding designs in the road industry. As a result, it requires the greatest care and attention in its design and construction
7. Superelevation Allow for Smooth Cornering
It helps to reduce both the maximum rear-enforce and the surface friction of a car on the tightest curve.
The reduction of friction is an indication of improved cornering performance, as well as a reduction in resistance during braking. It provides better control of the vehicle during wet conditions
Disadvantages of Superelevation:
1. Extra construction cost
Extra construction cost due to extra engineering and geological work and concrete construction is needed for superelevation
2. Can be Complex
If it is not done properly then it can cause loss of control of the vehicle or cause instability in the vehicle.
3. High Maintenance
This is caused due to additional wear on tires. It leads to increased costs of maintenance.
4. Requires more space
This will need extra spaces and can take more space for construction
5. Increases weight of vehicles
Increases weight of vehicles, which also increases traction forces on the road base by up to 20%
6. It can cause danger
This is caused due to extra wear on tires
Superelevation on Highway Engineering FAQs
1. What is the purpose of providing superelevation on roads?
Superelevation is also called crowning, camber, or banking. As the vehicle moves through a curve, it tends to follow the path of least resistance. The superelevation provides for a smoother transition from a straight road to a curved road.
The reduced amount of friction between the tires and the roadway allows for the vehicle to have greater traction without skidding in corners and curves.
2. What is the “crown” of a road?
The height differential between the center of a parking lane and the outside lane is called crowning. When drivers are going around corners, they naturally want to travel in the center of their lane.
This makes it important for roads to have adequate crowning. Without a proper amount of crowning, drivers may feel uncomfortable when driving through curves and corners.
3. What is the difference between superelevation and banking?
While most roads on the market have sufficient crowning, other roads do not. For example, small roads may not have enough crowning for vehicles to travel with less friction as they make turns.
Banks are used on these roads to increase the amount of friction that drivers experience as they go around a curve.
A good example of this is seen in intersections. While the banks may not be used for vehicle flow, they are put into place to slow down traffic.
4. Do cyclists benefit from superelevation?
Cyclists do benefit from superelevation, particularly in urban environments. A lot of urban roads have steep grades that increase the risk of crashes due to over-steering or under-steering.
One way to avoid this is to provide bicyclists with more superelevation.
5. What is the purpose of providing superelevation on roads?
The primary purpose of superelevation is to provide drivers with safer driving experiences.
It is important that there be enough friction between the tire and the roadway to provide drivers with a smooth transition from straight driving to curvy driving.
Without enough superelevation, drivers may feel nervous as they approach a curve in the road.
6. What is superelevation used for?
Superelevation is the banking of the roadway such that the outside edge of pavement is higher than the inside edge.
The use of superelevation allows a vehicle to move more safely and at a higher speed through a curve than would otherwise be possible.
7. What is maximum superelevation?
Max Superelevation The maximum allowable superelevation is the maximum change in grade or slope that a roadway can have.
This is also known as the maximum slope. Max superelevation is determined by state highway design policies, and the values vary depending on the types and conditions of travel lanes.
The maximum allowable superelevation is equal to 7% for plain and rolling terrain while that of hilly terrain is 10% and the urban road is 4%.
Superelevation can be used to reduce the effects of wheel slippage on curves and prevent fishtailing.
8. What is minimum superelevation?
Minimum Superelevation Minimum superelevation is the minimum amount of crown (superelevation) that is required on a curve.
This is typically determined by the smoothness of each curve, as well as the speed of traffic that travels through the curve.
Minimum superelevation is the lower limit of superelevation equal to the amount of camber. For drainage purposes, it is (2-4) percent, especially for large radius horizontal curves.
9. What causes a vehicle to skid when it takes a curve?
When there is too much or too little superelevation, it can cause vehicles to skid. Vehicles have more traction on flat surfaces.
When drivers take curves at high speeds, they want to be in their lane as much as possible to avoid accidents.
10. What is Superelevation in Highway Engineering?
The rotation of the pavement on the approach to and through a horizontal curve is known as superelevation.
Superelevation is intended to help the driver by compensating for the lateral acceleration caused by negotiating the curve.
The transverse slope created to counteract the effects of centrifugal force and lessen the likelihood of the vehicle to overturn and skid laterally outwards by increasing the pavement outside edge with respect to the inner edge is known as superelevation. The symbol for superelevation is ” e “.
11. What are the benefits of using the Super-Elevation?
The Super-Elevation is primarily used to help drivers feel more comfortable with their surroundings when they are driving.
They are also a good idea in areas that have a lot of curves. The Super-Elevation helps make corners and surface changes feel more gradual.