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Road gradient is the rate of rise and fall along the length of road with respect to the horizontal. In simple words, it is the slope provided longitudinally to the road formulation along its alignment, usually to connect two points situated at diﬀerent levels.

Rise with respect to horizontal distance is called Upward gradient or positive gradient or Ascending gradient and is denoted by (+n%). Whereas, fall with respect to horizontal distance is called Downward Gradient or negative gradient or descending gradient as and denoted by (-n %).

The gradient of the road is expressed as 1 in n (1 vertical unit to the n horizontal units). Sometimes it is expressed even in percentage also. If there is a rise or a fall of 1 m in a 100 m horizontal length, then the gradient will be expressed as 1 in 100.

• To link the places or locations which are located at diﬀerent levels.
• For smooth movement to vertical profile.
• To provide an eﬀective drainage of rainwater on roads, when the pavement of road is provided with Kerbs.

• Nature of the traffic – A gentle gradient should be provided where the traﬃc on the road is usually of slow-moving vehicles like bullock carts and bicycles.
• Drainage of water – The gradient of road provided should be steep in the areas where there is heavy rainfall.
• Appearance – It is necessary to provide a gradient to the road for its appearance and aesthetic beauty.
• Points like canals, bridges, railway crossings, etc.
• Topography of the area or the religion where the road is to be constructed.
• Safety of the traﬃc.

The vertical distance between two points divided by the horizontal distance between two points is known as the average gradient. The average gradient is generally used for the design of roads in hilly areas. The hilly areas have a relatively steeper slope.

Therefore,

Average gradient = The vertical distance between two points/The horizontal distance between two points.

The maximum gradient within which the designer attempts to design the vertical profile of the road is known as the ruling gradient. Ruling gradient is also referred to as design gradient.

It is generally used because it gives the utmost safety at the least possible cost. The ruling gradient depends upon the following factors:

• The type of terrain.
• The nature of traﬃc.
• Average speed of traﬃc.
• Types of vehicles, etc.

Due to the topography of a particular area, sometimes a gradient steeper than the ruling gradient is provided to the roads. This type of gradient is known as the limiting gradient.

There are a few circumstances in which it may be unavailable to provide still steeper gradients, at least for a short distance. In that case, the steeper gradients upon exception gradient may be provided.

The minimum required slope necessary for the eﬀective drainage of rainwater from the surface of the road is known as the minimum gradient. The minimum gradient is usually adapted where surface drainage is to be considered.

The descending gradient required to maintain the same speed of a vehicle, that was on the ascending gradient, without applying accelerators or brakes, is known as a floating gradient.

Diﬀerent gradients are provided to the roads in diﬀerent terrains. Some terrains require a steep gradient and some of them require a gentle gradient. So the gradients in diﬀerent terrains are provided accordingly. They are mentioned in the table below.