How to Design Road Camber ? Geometric Design of Highways

Camber or Cross-Fall is a convexity that is provided to the cross-section of a road. It is the level difference between the highest point of the road, the crown and the edge. Generally, crown forms the centre of the carriageway.

The cross-section of a road can either be curved or straight. Camber is expressed in terms of slope of the chord that joins the crown of the road with curved profile. It is expressed as slope of the actual surface of a road with straight profile.

It is expressed in 1 vertical to n horizontal that is expressed in percentage.

Read More: What is Camber and Its Importance?

Types of Road Camber and Their Design

Road camber can be classified into 4 types:

1. Straight line Camber or Sloped Camber

A straight line camber is made by the combination of two straight surfaces as shown in figure-1 (b) below. The central top portion of the profile is called as crown.

If R = rise of the crown, W = base of the cross-section, the slope is 1 : n, then

1/n = R/(W/2)

Hence, rise R = W/2n

Fig.1. Camber Types

2. Parabolic Camber Method

In this method, the cross-section of the road takes a parabolic shape. This type of camber is designed for roads that possess fast-moving vehicles. The value of parabolic camber is given by figure-1 (a)

y = 2x²/nw

Also Read:  Cross-Section of a Road – Geometric Design of Highways

3. Partially Straight and Parabolic Curve - Composite Camber

Here central part of the road is made parabolic and straight slopes near the edges. This to decrease the intensity of pressure by increasing the contacting area of the wheel.

Partially Straight and Parabolic Curve -  Composite Camber

As shown in the above figure, the profile is straight along the distance W-Xa and is parabolic along distance Xa.

Then for parabolic portion:

Y = nx²/2X_a ; Here, camber = 1/n;

For the straight Portion;

Y = nX – Flattening of the Crown = nX – 0.5nX_a

4. Two-Straight Line Camber

Two-Straight Line Camber

In the above figure, Y is an ordinate at a distance X from the crown. As shown, two similar straight lines are formed along W- X_a and two same straight lines along X_a distance on either sides.

Then Y = nX –Flattening of the Crown

Here the flattening of the crown is taken different of two straight lines, then Y is determined separately.

This method is found suitable for Indian roads, as this will ensure the contact area of the tyres with the road surface to be more compared to other camber design methods. This would facilitate less damage to the road surface.

Also Read: What is Geometric Design of Highways? Objectives and Design Elements