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SUPERELEVATION AND ITS DESIGN FOR HIGHWAYS

What is Superelevation in Highway Engineering?

To counter-act the effect of centrifugal force and reduce the tendency of vehicle to overturn and to skid laterally outwards, pavement outer edge is raised with respect to inner edge. Thus, providing a transverse slope is known as Super elevation. It is represented by “ e ”.

Superelevation in Highway Engineering

Analysis of superelevation

Let us say Design speed = V m/s

Radius = R m

Various forces acting on the vehicle:

Where e = rate of super elevation in %

f = lateral friction factor = 0.15

V = velocity of vehicle in m/s

g = acceleration due to gravity = 9.81 m/s2

R = radius of circular curve in meters.

Limits for maximum super elevation:

According to IRC the Maximum Super elevation in Areas

Which Are Bound by Snow fall – 7%

Which are not bounded by Snow fall – 10%

Limits for minimum super elevation:

Minimum super elevation = camber or cross slope

Camber: Slope provide in the transverse direction to drain off rain water quickly is known as Camber or Cross slope. This will also prevents slipping and skidding of vehicles.

IRC Recommendations for Camber:

Type of pavement	Light rainfall intensity	Heavy rainfall intensity
C.C pavements & thick bituminous pavements	1 in 60	1 in 50
Thin Bituminous Pavements	1 in 50	1 in 40
W.B.M & Gravel Pavements	1 in 40	1 in 33
Earthen Pavements	1 in 33	1 in25

Design of super elevation:

There are four steps involved in the design of super elevation. And they are,

Step 1:

Calculate the super elevation necessary for 75% design speed and assume No lateral friction is developed

If e value is less than emax = 0.07, provide calculated e value. Otherwise proceed to next step

Step 2:

When ecal > emax

Provide e = emax = 0.07 in this step and go to next step.

Step 3:

From the above step we have the value of e. so, check for lateral friction factor is applied in this step for the known value of e.

If fcal < fmax (0.15)

Then e = 0.07 is safe.

But if fcal > 0.15

Then restrict the values to f = 0.15, e = 0.07

And go to last step.

Step 4:

In this step we will find out the value of restricted speed.

Let V = Va

If Va > V, then e = 0.07, f= 0.15

If Va < V , then also e = 0.07, f = 0.15 but, speed restriction board is provided which consists the value of Va As shown in figure below.