What Is the Gradient of Road?

It is defined as the rate of rising or falls along the length of the road with respect to the horizontal is known as Gradient of Road. In another word, it is the longitudinal slope provided to the formation level of the road along its alignment. It is generally expressed in 1 in n ( where 1 is a vertical unit to n is a horizontal unit). It is also expressed in percentage.

Gradient = (Vertical distance / Horizontal distance) x 100

A road’s gradient rises or decreases with the road’s horizontal alignment. It’s the height difference between where you started and where you ended, expressed over the same length of time. A gradient is a rate at which a road goes up or down along its path. Slopes and other undulations on the land’s surface are the norms rather than the exception.

Errors may occur if a road is built there. The road’s gradient absorbs these fluctuations in altitude. To build highways, they must be included since they regulate the transitions between straight stretches. They answer problems like uneven terrain, flooding, high construction costs, and public discontent.

Purpose of Providing Gradient to the Roads

1. To connect the two stations or points with each other, which are located at different levels.
2. To provide effective drainage of rainwater, especially when the pavement is provided with the curbs.
3. To construct the side drains economically.
4. To make the earthwork required for the road construction economic by balancing cutting and filling.

Importance of Gradient in Roads

1. The gradient is the most important part of the construction of roads. It is essential to give properly required gradient to the road along the length of its alignment with respect to horizontal.
2. Gradient allows movement of the vehicle on the vertical curves smoothly.
3. The gradient also helps to drain off rainwater from the surface of the roads.
4. Gradients are very helpful on curved roads in flat terrain where drainage problem arises.
5. Before finalizing the gradient of the road, it is important that the construction cost, vehicular operation cost, and the practical problems that may arise on the site also have to be considered.

Effect of Gradient on Roads

1. The effect of gradient on the vehicular speed is considerable. This is particularly important in roads where the proportion of heavy vehicles is significant.
2. Due to less sight distance at uphill gradients, the speed of traffic is generally controlled by these heavy vehicles. Due to which the operating costs of the vehicles are increased, and the capacity of the roads will have to be reduced.
3. Due to high speed between heavy and light vehicles, and between uphill and downhill gradient accidents abound in the gradients.

Factors Affecting Gradient

1. Nature of the ground.
2. Drainage required.
3. Nature of the traffic.
4. The type of road surface.
5. The total height to be covered.
6. Road and railway interaction.
7. Safety Required.
8. Bridge Approaches.

Irc Recommendations for Gradient

IRC had specified desirable values for different types of terrains.

Types of Road Gradient

The types of road gradient are as follows

1. Ruling Gradient.
2. Limiting Gradient.
3. Exceptional Gradient.
4. Average Gradient.
5. Floating Gradient.
6. Minimum Gradient.

1. Ruling Gradient

The gradient, which is usually adopted while making the alignment of the road, is known as the ruling gradient. The ruling gradient is used for designing the road because it gives maximum safety at minimum cost.

2. Limiting Gradient

The gradient, which is steeper than the ruling gradient, is known as the limiting gradient. In some situations, we cannot adopt the ruling gradient, where we have to use a limiting gradient. It is usually used in hilly terrain and rolling terrain. The topographical condition of a place compels adopting the steeper gradient. It is also known as the maximum gradient.

3. Exceptional Gradient

The gradient, which is steeper than the limiting gradient, is known as the exceptional gradient. This type of gradient is generally used in an extraordinary situation where shorter lengths of the roads are available.

Exceptional gradients are a very steeper gradient that is used in the unavoidable situation like in the mountainous region and terrain. But the drawback of an exceptional gradient is that it required more fuel consumption and has more friction losses.

4. Average Gradient

The total rate of rising or fall between any two points along the alignment of the road divided by the horizontal distance between two points is known as an average gradient.

5. Floating Gradient

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

6. Minimum Gradient

The minimum desirable slope which is essential for the effective drainage of rainwater from the surface of the known as a minimum gradient. It is usually adapt where surface drainage is important.

FAQ: Road Gradients

What is the gradient of a road?

The gradient of a road is the rate of rise or fall along the length of the road with respect to the horizontal. It is expressed as a ratio (e.g., 1 in n) or as a percentage.

How is the gradient of a road calculated?

The gradient is calculated using the formula: Gradient = (Vertical distance / Horizontal distance) x 100.

Why is the gradient important in road construction?

The gradient is crucial for connecting points at different elevations, ensuring effective drainage, balancing cutting and filling in earthwork, and managing construction costs.

What are the main types of road gradients?

The main types include:

1. Ruling Gradient: Commonly used for designing roads, offering maximum safety at minimum cost.
2. Limiting Gradient: Steeper than the ruling gradient, used in challenging terrains.
3. Exceptional Gradient: Steeper than the limiting gradient, used in extraordinary situations.
4. Average Gradient: The overall rise or fall rate divided by the horizontal distance.
5. Floating Gradient: Allows a vehicle to maintain a constant speed without power or brakes.
6. Minimum Gradient: Necessary for effective drainage.

What factors affect the gradient of a road?

Factors include the nature of the ground, required drainage, type of traffic, road surface, total height to be covered, road-railway interactions, safety requirements, and bridge approaches.

What are the IRC recommendations for gradients in different terrains?

Plain or Rolling Area:

1. Ruling: 1 in 30 (3.3%)
2. Limiting: 1 in 20 (5.0%)
3. Exceptional: 1 in 15 (6.7%)

Mountainous Area:

1. Ruling: 1 in 20 (5.0%)
2. Limiting: 1 in 16.7 (6.0%)
3. Exceptional: 1 in 14 (7.0%)

Steep Area:

1. Ruling: 1 in 16 (6.0%)
2. Limiting: 1 in 14.3 (7.0%)
3. Exceptional: 1 in 12.5 (8.0%)

How does the gradient affect vehicular speed on roads?

Steeper gradients can reduce vehicular speed, particularly for heavy vehicles, affecting overall traffic speed and increasing vehicle operating costs.

What is the purpose of providing a gradient to roads?

The gradient connects points at different elevations, facilitates effective drainage, and balances earthwork, making road construction economical.

What is a floating gradient?

A floating gradient is one on which a vehicle can descend at a constant speed without the need for power or brakes.

Why is the minimum gradient important?

The minimum gradient ensures effective drainage of rainwater from the road surface, which is crucial for road safety and longevity.

1. What is the difference between ruling, limiting, and exceptional gradients?
2. Ruling Gradient: Standard gradient used for most road designs.
3. Limiting Gradient: Steeper than ruling, used when ruling gradients are not feasible.
4. Exceptional Gradient: Steeper than limiting, used in exceptional and unavoidable situations.