What is Superelevation? It’s importance, Design & Analysis.

Superelevation:- its design and analysis

Superelevation is used in highway engineering to make highways safe so that vehicles can maintain their optimal speed.

They are basically used on the curve or bends on the highways to counteract the centrifugal force generated by the vehicle at the time of turning.

They are very important for others to prevent overturning, skid, rollover of the vehicle in slippery, wet, and icy conditions.

Icy Roads

It also prevents slowing down of vehicles on the bends and curves, which eventually causes traffic jams due to slowing down the speed of the vehicle.

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What do you mean by Superelevation?

It is a part of highway construction used on the curves in which the outer part of the curve is raised than the inner part of the curve as per the design of the highway.

To provide proper stability to the vehicles and prevent accidents due to sudden forces like centrifugal and centripetal forces.

As these forces suddenly act on the vehicle, especially on the curves to counteract these forces, superelevations are provided.

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Why We Need Superelevation?

  • By providing superelevation on roads, we ensure the safety and placidity of the moving traffic.
  • As it reduced the wear and tear of pavements on the curves of the roads, which results in low maintenance cost.
  • It also prevents the accidents due to overturning, rollover and skids.
  • As it is provided mainly to counteract the complex forces coming on the road due to vehicle movement.

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How This Works?

There are several complex forces acting on the vehicle which become the cause of skidding, rollover, or any type of mishappening on the curve due to the high speed of the vehicle.

Superelevation working depends on following factors, these are as follows:-

  • Velocity of the vehicle.
  • Weight.
  • Inertia.
  • Centripetal Force.
  • Centrifugal force.
  • Friction.

It is designed by keeping these factors in mind as these all factors are interacting with the fast coming vehicle.

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Maximum and Minimum Superelevation

The maximum and minimum value of superelevation is depended on various factors, these factors include camber.

Camber is provided more than the superelevation for the proper drainage as the improper drainage leads to the water clogging which later affects the roads.

The rate of superelevation must be lower in the case of heavy vehicles, as the heavy vehicle has more density and a high center of gravity.

So, for safety purposes of heavy vehicles, rates of superelevation just are lower in the curves.

For the express highways or flat roads where the radius of curves is very large then the value of superelevation must be negligible.

There should be a maximum limit for the superelevation as per the environmental exposures of the roads as well as vehicle movements.

Indian Road Congress (IRC) has set some rules and regulations for the superelevation to prevent future errors while designing the highways.

Which can later lead to fatal accidents and can compromise the road safety of the people.

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IRC Recommendations

There are certain recommendations regarding designing of the highway. Which includes radius in a meter of camber, the recommendation for cambers.

IRC Recommendation for the radius in a meter of camber
Recommendations for the type of pavement as per exposure

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Designing of Superelevation

There are four steps regarding the designing of the superelevaton of the highway:-

Step-1:- The designing of the superelevation is done according to 75% of the final design speed of the vehicle.

e= Rate of Superelevation in Percentage.
f= Factor of lateral friction.
R= Radius of Curve.
V= Velocity of Vehicle.
g= Acceleration Due to Gravity.

Step-2:-The value of ecal > emax is provided e = emax = 0.07 in the equation then you move to further steps.

Step-3:- In the above step, we’ve calculated the value of e. Therefore now, we check for the side friction factor in the above formula for the known value of e.

We’ve calculated the value of fcal therefore, fcal < fmax (0.15). If fcal > 0.15 Then restrict the values to f = 0.15, e = 0.07, and we directly go to the last step.

Step-4:- In this final step, we’ll find out the final or restricted speed of the vehicle.

 After getting the value of Va in this formula. If Va > V, then e = 0.07, f= 0.15 If Va < V, then also e = 0.07, f = 0.15.
Therefore, This restricted speed is shown in the signage by the NHAI on the highways or expressways.

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After reading this article, whenever you are traveling on the highway or calculating the restricted speed of the roads/superelevation by using the above formulas.

You will be amazed by the results as each step and formula are elaborated in its own means.

If you have a query regarding this article, please comment below.

By Shivansh Sharma

Shivansh Sharma is a Civil Engineer who is a Structural Engineering enthusiast, Blogger, and learner. Pursuing M. Tech (Structural Engineering). His project portfolios include 3 Residential projects and 1 commercial project. His knowledge of Rehabilitation of structures, Concrete, Steels and construction techniques allows him to help clients to meet their needs. Being a nature lover If he isn't working you will probably find him in the garden with his plants.


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