Definition, Types and Benefits of road cambers in highway

It is mostly found in the highways that the median part of the road surface is elevated with regards to the edges. This slope in the diagonal direction is known as the Camber (or Cant). The purpose of the camber is to drain out the rainwater from the road surface around the edges.

Camber is the slope provided to the road surface in the transverse direction to drain off the rainwater from the road surface. It is also known as cross slope of road.

The rate of camber is normally indicated by 1 in n (1 vertical to n horizontal) or in proportions as n% (for instance, 1 in 50 or 2%). The design values of cambers are primarily based on the type of the pavement and also on the average amount of the rainfall in the area. Steep cambers are useful for eliminating surface water. But they are not recommended since they will wear down the surface. Normally, cambers of slope 2 to 3% are arranged. On straight sections of roads, there are shoulders with higher cross fall relating to that of the carriageway by 0.5%.

The benefits of cambers :-

To take out the rain water from the pavement surface rapidly.
To resist entering of water into gravel and bituminous roads by exhausting the surplus water speedily.

To resist entering of surface water into sub-grade soil in the course of pavement.
As a safety measure, wet pavement conditions are not suitable from safe driving standpoint.
To make pavement surface good-looking.

The cross-section shape of the transverse or cross slope ranges from curved, straight or a composite of both. The median portion of the road that is elevated is known as the crown.

Categories of camber: The cambers along the road surface are categorized as follow :-

Straight line camber: These are arranged with two identical standardized straight line slopes at both sides of the crown and are also called as Plane cross slopes. They are suitable for very flat slopes like PCC or RCC Pavement.

Parabolic Camber: In parabolic camber, the cross slope remains in the form of simple quadratic parabola. Under this situation, the ordinate Y fluctuates as the square of abscissa X (simple parabola equation).

It offers a flat road surface at the center and steeper towards the edges. As a result of steeper edges, this type of camber comes with superior evacuation property.

Parabolic cambers are most effective for speedy moving highways. A beneficial situation for overtaking operation is allowed because of the curved cross slope. Since the slope expands externally to the road edge, the flow of surface water ahead of the pavement is improved. One drawback of parabolic cambers is that the construction process is very complicated.

Composite camber: Composite camber is made of partially parabola and partially straight line or two straight lines with different slopes. Usually, middle part of the road is created as parabolic and arranged with straight slopes near edges. It results in eliminating amount of pressure by raising the contact area of the wheel.