What is Gradient of road?
The slope of the road pavement in the longitudinal direction is called gradient or grade. It may be expressed either as a ratio of rise or fall in a specified horizontal distance. When a road ascends 1 meter in every 20 horizontal distance it is called 1 in 20 upgrade or 5% upgrade. Similarly, if road descends 1 meter in every 10 horizontal distance it is called 1 in 10 downgrade or 10% downgrade. The gradient of road depends on nature of traffic, nature of ground and rainfall of the locality.
Types of gradient in highway engineering :
1. Minimum Gradient : It is an essential gradient to be provided in the longitudinal direction of the road pavement to drain off rain water easily. A minimum gradient of 1 in 250 (0.4%) for flexible pavements and 1 in 300 (0.33%) for rigid pavements is desirable.
2. Limiting or maximum gradient : This is the steepest gradient which is to be permitted on the road.
3. Average Gradient : The total rise or fall between any two points chosen on the alignment divided by the horizontal distance between the two points is called average gradient.
4. Ruling Gradient : The suitable gradient which may be normally provided in the alignment of a road and in such a way that the vehicle may negotiate long stretches of the gradient without much fatigue.
5. Exceptional Gradient : The gradient less than minimum gradient and more than maximum gradient is called exceptional gradient. The maximum length of an exceptional gradient should not exceed 60 meters in 1 km road length. The exceptional gradient becomes necessary to avoid deep cuttings.