# 6 Types of Classification of Gradient – Ruling, Limiting, Exceptional, Minimum, Average and Floating Gradient

## 6 Types of Classification of Gradient

The gradient is divided into the following 6 categories

Following 6 types of the gradient are described below:

The gradient usually adopted while making the road alignment is called the ruling gradient. It is the maximum gradient within which the designer attempts to design the vertical profile of a road. It is also known as design gradient. As per IRC, the recommended value of ruling gradient for plain or rolling terrain is 1 in 30 or 3.3 %.

The gradient steeper than the limiting gradient which may be used in a short length of the road, only in an extraordinary situation is called exponential gradient. This type of gradient is adopted only in a very difficult situation and for a short length not exceeding 100 m at a stretch. As per IRC, the recommended value of Exceptional gradient for plain or rolling terrain is 1 in 15 or 6.7 %.

The minimum desirable slope essential for effective drainage of rainwater from the road surface is called minimum gradient. The desirable minimum gradient for this purpose is 0.5 % if the side drains are lined and 1 % if the side drains are unlined.

It is the ratio of total rise or fall to the horizontal distance between any two points along the alignment of the road.

The gradient on which a motor vehicle moving with a constant speed continues to descend with the same speed without any application of power brakes is called floating gradient.

### FAQs

#### What is meant by ‘1’ in ‘n’ gradient?

In simply, 1 refers to the vertical rise, and n refers to the horizontal distance(run). For ‘n’ units horizontal distance the verticle rise will be ‘1’ unit.

The gradient in the roads can be represented as a percentage or as 1 in n. First of all, you need to calculate the horizontal distance corresponding to the vertical rise. For example, if the measured horizontal distance(run) is ‘4’ units and the corresponding verticle rise is ‘1’ unit, then the gradient of the road will be 1 in 4. If you want to convert it into a percentage, then divide the rise by run, and multiply with 100. In the above case, it will be [(1/4)*100] = 25 %.

#### What is the value of limiting gradient for steep terrain?

The recommended value of limiting gradient for steep terrain is 1 in 14.3 or 7%.

#### What is the value of limiting gradient for Rolling terrain?

The recommended value of limiting gradient for rolling terrain is 1 in 20 or 5%.

#### What is the value of exceptional gradient for rolling terrain?

The recommended value of exceptional gradient for rolling terrain is 1 in 15 or 6.7%.

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