Camber value and disadvantages of heavy camber

Camber (cross fall) is the transverse slope given to the carriageway on a straight road, with the centre (crown) higher than the edges, so that rainwater drains quickly to the side drains. It is expressed as a percentage or ratio (e.g. 2.5% or 1 in 40).

How the camber value is decided

1. Type of road surface: impervious, smooth surfaces (cement concrete, good bituminous) need less camber; rough or pervious surfaces (WBM, gravel, earth) need more.
2. Amount of rainfall: heavier rain needs a steeper camber.
3. Longitudinal gradient: a steep longitudinal gradient also drains water, so a smaller camber is enough on steep roads.
4. Traffic speed and volume: high-speed roads have flatter camber for stability.
5. Cost and construction convenience: the camber is a compromise between drainage and comfort.

(NRS 2070 gives its own values by surface type; about 2.5% is common for paved roads in Nepal.)

Disadvantages of heavy camber

1. Uncomfortable and unsafe driving: vehicles tend to slide sideways, especially in wet weather and at speed; steering is difficult.
2. Vehicles crowd the centre of the road to avoid the slope, causing wear at the centre and risk of head-on crashes.
3. Overturning risk for high vehicles when passing or overtaking on the slope.
4. Uneven pavement wear: the load of the wheels is concentrated at the centre and the pavement deforms.
5. Erosion: water runs fast, scouring the surface and shoulders.
6. Higher cost: more earthwork and pavement material, and the crown is hard to make at the junctions.
7. Difficult to cross the road or turn at intersections.