What Is Road Gradient?
The rate of rise and fall with respect to the length of the road is termed as gradient of the road. The road gradient is naturally expressed in the term of 1 in n term where 1 is the vertical unit and the ‘n’ represents the horizontal units.
So, in mathematically gradient + ( vertical / horizontal distances) X 100
Purpose of Providing Road Gradient
Here, the providing road gradient are as follows.
- The points or stations which are located, at different positions: to connect those points we need to use road gradient.
- For the drainage system of the road, we use gradient specially in the kerb portion.
- It neutralizes the process of cutting and filling in the construction of road.
- To create economic drain beside of any road.
Importance of Gradient in Road
Here, the importance road gradient are as follows.
- It is one of the most important parts of road construction. In every road gradient, we need to provide a proper gradient.
- Road gradient allows all the vehicles to go in vertical curves or steeper paths.
- To clean up the rainwater from the road: gradient carries an important role.
- A gradient is basically provided after finalizing the construction cost, practical problems, vehicle operation cost, etc are considered.
Effect of Gradients on Roads
Here, the effect of road gradient are as follows.
- By providing the road gradient we must consider the vehicle speed.
- The fuel consumption of the vehicles are higher in the gradient portion considering to the flat road.
- Due to high speed between heavy and light vehicles in the uphill and downhill portion, maximum accidents are happened.
Factors Affecting Gradient
Here, the factors of road gradient are as follows.
- Proper drainage required
- Type of road surface
- Nature of the ground surface
- Nature of the traffic
- Railway and road interaction
- Bridge approaches
- Safety required in the gradient
Road Gradient Recommendations as Per IRC
Nature of Ground
Plain or rolling terrain
|1 in 30||1 in 20||1 in 15|
|1 in 20||1 in 16.7||1 in 14|
|1 in 16||1in 14.3||1 in 12.5|
Also Read: What Is Bituminous Road? | Bituminous Road Construction | Bituminous Road Layers | Bituminous Macadam | Bituminous Road Construction Process | Advantages of Bitumen Road | Disadvantages of Bitumen Road | Application Road
Types of Road Gradient
Gradients are mainly categorized into six categories, those are-
1. Limiting Gradient: A limiting gradient is that type of gradient which is steeper than ruling gradient. This limiting gradient is mainly used in rolling terrain and hilly terrain. This gradient is also known as a maximum gradient. The limiting gradient is steeper than ruling gradient.
2. Ruling Gradient: A ruling gradient is that type of gradient which is used to make the alignment of the road. This is adopted widely because this gives maximum safety at minimum cost. It is only provided after a proper topographical study and traffic study. The ruling gradient is mainly obtained for the locality. The IRC recommendation for the ruling gradient is- In flat or rolling terrain- 1 in 30 Hilly terrain- 1 in 20
3. Exceptional Gradient: An exceptional Gradient is that type of gradient which is steeper than limiting gradient, this is used in only for a special situations. This gradient is adopted in unavoidable situations like mountainous terrain that’s why the gradient is steeper ad it causes more fuel requirement and frictional losses.
4. Average Gradient: The rate of fall or rise between two points along the road alignment is known as average gradient.
5. Floating Gradient: Floating gradient is a gradient where vehicles are moving smoothly with constant speed without using braking or other application. It also saves the energy of the machine.
6. Minimum Gradient: A minimum gradient is that type of gradient where we provide a minimum slope for the drainage purposes of rainwater. This gradient is mainly provided in the plain roads for drainage purposes of rainwater. The gradient value depends on the soil type, topographical condition, run-off, and other parameters. Generally, we provide 1 in 200 slope for the minimum gradient but in the cement concrete surface grade, it becomes 1 in 500.
7. Steeper Gradient: This type of gradient are very inconvenient for traffic movement because here all the traffic speeds are lesser in this gradient. In this type of gradient, we need a massive earthwork operation for construction. The IRC recommendation for this type of gradient is – In flat or rolling terrain- 1 in 20 In hilly terrain- 1 in 15
All Advantages and Disadvantages of the Road Gradient
Advantages of Rulling Gradient
- Ruling gradient is the desirable upper limit of the gradient in the road alignment.
- Ruling gradient is mainly done for the locality purpose usage.
- This type of gradient can reduce the accidents in the roads.
Disadvantages of Rulling Gradient
- This type of gradient needs a proper design by experienced engineers and it can only provide after a proper traffic and topographical study.
Advantages of Limiting Gradient
- The main advantage of the ruling gradient is to minimize the road construction cost
- Limiting gradient is steeper gradient provides a wonderful view.
Disadvantages of Limiting Gradient
- This is a steeper gradient so it is used for limited road length.
- Due to the steeper slope fuel consumption and maintenance is also increased.
Advantages of Exceptional Gradient
- Exceptional gradient is mainly done when a unavoidable situation arrived: this is the main advantage of the exceptional gradient.
- This type of gradient is limited; this should not exceed 100 meters in a stretch
Disadvantages of Exceptional Gradient
- Too many cutting filling operations are required to execute this type of gradient.
- It requires more labor cost than other ones.
Advantages of Minimum Gradient
- The main advantage of this gradient is proper drainage of rainwater from the roadway.
- For proper drainage system the longevity of the road is increased.
Disadvantages of Minimum Gradient
- Though is has some specific function but it requires some extra cost.
Advantages of Floating Gradient
- In this type of gradient a motor vehicle can move smoothly without using extra energy or applying brakes.
- This type of gradient reduces vehicular damage.
Disadvantages of Floating Gradient
- The number of accidents can increase due to more speedy transportation.