Camber or cant is the cross slope provided to raise middle of the road surface in the transverse direction to drain off rain water from road surface and keeps cars from sliding and causing damage to the pavement. It has a lot of benefits that make the road surface last longer. Generally, a camber is a crown-shaped part of the road surface that is made by raising the middle of the road compared to its edges. Most of the time, the rate of camber or cross slope of a road is written as “1 in n,” which means that the transverse slope is in the ratio of 1 vertical to n horizontal or it can be written as a percentage. For example, a road with 2.5% camber has a camber of 1 in 40. Too steep slope is undesirable because it will erode the surface. The common types of camber are parabolic, straight or combination of them. The objectives of providing camber are given below.
- Surface protection especially for gravel and bituminous roads
- Sub-grade protection by proper drainage
- Quick drying of pavement which in turn increases safety
Required camber depends on
- Type of pavement
- Amount of rainfall
The values suggested by IRC for various categories of pavement are given in Table 1.
Table 1 - IRC Recommended Values of Camber in Road for Different Types of Road Surfaces
|
Type of Road Surface |
Range of Camber in Areas of |
|
|
Low Rainfall |
Heavy Rainfall |
|
|
Cement concrete
and thick bituminous surface |
1 in 60 or 1.7% |
1 in 50 or 2.0% |
|
Water
bound macadam and gravel pavement |
1 in 40 or 2.5% |
1 in 33 or 3.0% |
|
Thin bituminous surface |
1 in 50 or 2.0% |
1 in 40 or 2.5% |
|
Earth Road |
1 in 33 or 3.0% |
1 in 25 or 4.0% |
Types of Camber in Road
1) Sloped or Straight Camber
Straight line camber comprises two slopes that come from the edges and meet in the middle of the carriageway. It is the simplest type of camber. It is easy to build and easy to keep in good shape.
2) Parabolic or Barrel Camber
It is a continuous elliptical or parabolic curve. It provides a level roadway in the centre and gradually rises to a steeper grade on the road’s periphery. Greater drainage efficiency results from the sharper edges of this camber type. Faster vehicles prefer this camber, so it is recommended for city streets. Maintaining and building a camber like this is challenging. Barrel camber is less user-friendly due to its sharper corners. Also, extra curbs are needed because the sharper the edge, the faster it will be damaged if it is not protected.
3) Composite Camber
Composite camber could be part parabola and part straight line or it could be made up of two straight lines with different slopes. Most of the time, the middle of the road is made to be parabolic and the edges are given straight slopes. It helps to lessen the force of the pressure by making the wheel’s contact area bigger.
