We have seen almost all highways being raised in the middle portion of the road surface with respect to the edges. This cross slope in the transverse direction is called as the Camber (or Cant). It is generally provided with the sole purpose of draining the rain water from the road surface towards the edges.
Protection of the road surface, especially for gravel and bituminous roads by draining the unwanted water as quickly as possible.
Protection of the subgrade by providing good drainage conditions.
For safety considerations, as wet pavement conditions are quite undesirable from safe driving point of view.
The cross-section shape of the transverse or cross slope can be curved, straight or a combination of both. The central part of the road which is raised is called the crown.
The cross slopes can be expressed in slope as 1 in n or in percentages as n% (for example, 1 in 50 or 2%). The design values of cambers mainly depend upon the type of the pavement and also on the average amount of the rainfall in the area. Steep cambers are effective in quick removal of surface water but are undesirable as they will erode the surface. Generally, cambers of slope 2 to 3% are provided. On straight sections of roads, shoulders are provided with higher cross fall than that of the carriageway by 0.5%.
Camber, % 1.5 to 2% 2 to 3 % 4% 5%
Excessive camber should not be provided unnecessarily because of the following reasons:
tan\theta= R/W
n=tan\theta=R/(W/2)
Also, tan\theta=Y/X
or, Y/X=R/(W/2)=n
Hence, Y=nX}
Y/X^2 =R/(W/2)^2
Y/X^2 =4R/W^2
∴Y=4R/W^2 X^2=\{(2\ast2R)/(W \ast W)\} X^2
Y=\{2R/(W\astW/2) \}X^2=(2n/W)X^2
∴Y=(2n/W) X^2
Parabolic cambers are designed for fast moving highways. A favourable condition for overtaking operation is provided due to the curved cross slope. As the slope increases outward to the road edge, the flow of surface water away from the pavement is enhanced. One disadvantage of parabolic cambers is that they are very difficult to construct.
Other objectives of providing camber are:
Protection of the road surface, especially for gravel and bituminous roads by draining the unwanted water as quickly as possible.
Protection of the subgrade by providing good drainage conditions.
For safety considerations, as wet pavement conditions are quite undesirable from safe driving point of view.
The cross-section shape of the transverse or cross slope can be curved, straight or a combination of both. The central part of the road which is raised is called the crown.
The cross slopes can be expressed in slope as 1 in n or in percentages as n% (for example, 1 in 50 or 2%). The design values of cambers mainly depend upon the type of the pavement and also on the average amount of the rainfall in the area. Steep cambers are effective in quick removal of surface water but are undesirable as they will erode the surface. Generally, cambers of slope 2 to 3% are provided. On straight sections of roads, shoulders are provided with higher cross fall than that of the carriageway by 0.5%.
Values of cambers depending upon the type of pavement
Pavement type Cement concrete Bituminous Gravelled EarthenCamber, % 1.5 to 2% 2 to 3 % 4% 5%
Excessive camber should not be provided unnecessarily because of the following reasons:
tan\theta= R/W
n=tan\theta=R/(W/2)
Also, tan\theta=Y/X
or, Y/X=R/(W/2)=n
Hence, Y=nX}
Parabolic Camber
In parabolic camber, the cross slope is in the shape of simple quadratic parabola. In this case, the ordinate Y varies as the square of abscissa X (simple parabola equation).parabolic camber
Y/X^2 =R/(W/2)^2
Y/X^2 =4R/W^2
∴Y=4R/W^2 X^2=\{(2\ast2R)/(W \ast W)\} X^2
Y=\{2R/(W\astW/2) \}X^2=(2n/W)X^2
∴Y=(2n/W) X^2
Parabolic cambers are designed for fast moving highways. A favourable condition for overtaking operation is provided due to the curved cross slope. As the slope increases outward to the road edge, the flow of surface water away from the pavement is enhanced. One disadvantage of parabolic cambers is that they are very difficult to construct.
