Road Gradient With Its Types For Highway Design : An Overview

A road gradient is very important in its own existence. Usually, the land topography is not straight. With a changing magnitude, it is quite common to have slopes. Constructing a road on such land can result in accidents. With the help of road gradients, these elevation-changes are smoothened to provide a “smooth vehicle movement.”

What Is A Road Gradient?

A road gradient is a longitudinal slope provided to the formation level of a road along its alignment. (w r eng. 2020). “Gradient of Road is defined as the rate of rising or falls along the length of the road with respect to the horizontal alignment”.It is the verticality experienced during travel, spread over the Corresponding horizontal distance. As shown in the diagram;

If “1.” represents the vertical unit and “b” represents the horizontal units, the road gradient would be the ratio of 1. The “α” represents the angle of deviation, that is, the angle between the diagonal and the horizontal plane “b.” It measures the road gradient in degrees of elevation, or depression, above or below, the horizontal plane.

Arguably, the road gradient is an essential aspect to consider when building a new road. And different conditions call for a specific type of gradients, which brings us to the next section: types of gradients.

Road gradient is also expressed in,

Gradient = (Vertical distance / Horizontal distance) x 100

Types of Gradients

There are six gradient types, as follows:

Ruling Gradient

The ruling Gradient is the most commonly adopted Gradient by engineers, among the six gradient types discussed here. The Gradient maximizes safety while minimizing the construction expense. It depends on the ground’s exact nature, the variety of vehicles, and the total height to be covered.

Limiting Gradient

When the ruling Gradient cannot be adopted due to the area’s prevailing topographical conditions, a steeper gradient is chosen. It is known as the limiting Gradient. It is frequently utilized in rolling and hilly terrain.

Exceptional Gradient

During unavoidable situations, such as those caused by mountainous terrain, too high slopes are used during constructing roads, which are called exceptional gradients.

Floating Gradient

This variable refers to a gradient where a car, during its descent, will continue to move at a constant speed without the application of power brakes. The traction required to maintain momentum will be equivalent to the vehicle’s resistance force with this Gradient.

Minimum Gradient

This Gradient is critical for longitudinal drainage, without which water would otherwise accumulate, instead of flowing into the side drains. It is the lower limit gradient for all roads. It depends on the amount of precipitation, the accompanying soil’s nature, and other topographical attributes.

Average Gradient

It is calculated by dividing the road gradient between 2 points, with the horizontal distance between the 2 points.

Each type has its intricacies, but the road gradient, in general, has a particular use and purpose that makes it an essential consideration during the road-construction process.

The Function of the Road Gradient

The road gradient is essential to allow vehicles to travel between different levels of elevation smoothly. Without it, heavier vehicles would find it practically impossible to transverse areas with excess changes in height. Additionally, for adequate drainage, road gradients are indispensable. Otherwise, water would steadily stagnate. It would cause problems for travelers but would also erode the road itself over time. It is a particular problem in flat areas that have curved roads.

The side drains’ construction is also dependent on road gradient, as the slope dictates the direction that the water would flow towards it. Moreover, the Gradient is just as essential to manage and control the road and the public’s construction cost in vehicular operation cost or any other practical problems during the road’s lifetime.

All of these aspects are wholly pertinent to and are addressed by the road gradient. It allows for the ascertainment of costs and precisely what variety of Gradient should one apply. A minimum gradient will take care of drainage problems, along with the cost-effective construction of the drains themselves.

The distinction is made between the ruling Gradient, the limiting Gradient, and the exceptional Gradient, based on various things, including the nature of the soil, traffic conditions, the type of road surface, the actual elevation of the land, the interaction between the road and the railways, and the general safety precautions. As all things have merits and drawbacks, the road gradient is no exception.

Factors Affecting Gradient

• The type of road surface
• Drainage required
• Nature of the ground
• Nature of the traffic
• Safety Required
• Road and railway interaction
• Bridge Approaches
• The total height to be covered

Advantages and Disadvantages Of Road Gradient

The road gradient allows a diverse range of vehicles to travel between different levels of elevation. An increase in heavier vehicles and speed can cause accidents on the slopes due to poor sight-lines. With a higher presence of heavier vehicles, the average speed

It is reduced, increasing the costs of operating vehicles. The efficiency of the engine also reduces. Additionally, the advantages are entirely dependent upon the correct implementation by the engineer. Meaning, a miscalculation can lead to significant repercussions in the future, and measures to save costs in materials could end up causes higher prices due to repairs. And it is not right to discount practical judgment and foresight.

The distinction between applying a ruling gradient or a limiting gradient can make, or break, the entire undertaking. It is because an inappropriate limiting gradient would lead to higher unneeded costs. Similarly, an inappropriate ruling gradient would lead to the public’s endangerment, as a steeper grade was required than what was provided. In particular, ruling gradients can reduce costs, however, only to the degree that the topography allows.

Exceptional gradients can significantly raise fuel consumption and friction losses. These losses lead to further increases in fuel consumption and emissions that increase motor vehicles’ environmental costs.

In summation, road gradient is an essential component of constructing roads, as they govern every aspect of the connection between the flat segments of roads. They are the solutions to changes in elevation, adequate drainage, controlling costs of construction, and managing any public issues. With all of its flaws, the Gradient remains the best and most practical solution to this matter of infrastructure.

Furthermore, each type of slope is made with immense consideration to the prevailing conditions and the people. Therefore, it has enabled humanity to remain unencumbered by changes in topography.

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References

1. (2017, August 20). What is Gradient and what types of Gradient in transportation engineering? Retrieved from Civil Engineering Hub: https://civilengghub.blogspot.com/2017/08/what-is-gradient-and-types-of- gradient.html.
2. Satya, M. (2019, November 23). Floating Gradient. Retrieved from Civil Engineering: https://civilnoteppt.com/floating-gradient/.