What is the Gradient of the Road and Types of Gradient of Road
The gradient on the road is the rate at which the road goes up or down along the road’s length. The gradient on the road increases or decreases along with the horizontal alignment of the road. The gradient on the road is also referred to as the height differences between where the road has been started and where it has been ended, and this is expressed over the same length of time. Errors can occur in the case of constructing the road on the slopes or other undulations on the land’s surface.
The gradient on the road helps to absorb these fluctuations in the altitudes. In addition, the road gradient also helps regulate the transitions between straight stretches during highway construction.
Importance of road gradient
➢ The road gradient is the most important part of the road construction process. In this context, it is necessary to ensure that the road has the right slope.
➢ The road gradient helps to allow the vehicle to move smoothly around the corner of the road.
➢ The slopes on the load surface also help to allow the drain off the water from the road after it rains.
➢ The road gradient is very effective on the road, along with the sharp turns in the flat areas, as well as it also helps to deal with the water drainage problems.
➢ The cost estimation is crucial for the road construction before deciding the slopes of the road.
Factors influencing road gradient
Road types
The road types also help to influence the gradient on the road. In the case of the high-speed motorways, the maximum disable road gradient is about 3%, whereas, in the case of the all-purpose single-carriageway roads, the desirable road gradient is about 6%.
Drainage system
The water drainage system also helps to influence the proposed gradient on the road. In the case of the road, it has been designed in the place where the water drainage attenuation is crucial, it is recommended that the road needs to be designed on the embankment for accommodating the large size attenuation pond.
Ground topography
The ground topography also influences the proposed road gradient. The ground topography helps to represent the steep hilly terrain. In this regard, the road profile required to be within the maximum range of the road gradient.
Traffic conditions
General road gradient can be provided in the case of the traffic condition on the road, if there are slow-moving vehicles, including bicycles and bullocks.
Appearance
The road gradient has also been provided to the road due to its aesthetic beauty and appearance.
Effects of road gradient
➢ The gradient on roads has a significant impact on the rates at which the vehicles have travelled. In this conext, special attention is needed on the road along with the high concentration of vehicles.
➢ In the case of the reduction of the road’s visibility, the speed of the large vehicles has been reduced. In this regard, the running expenses of the vehicles have risen and the capacity of the road has decreased.
➢ The occurrence of accidents is common in the grades due to the high speeds between large and light vehicles and between the downhill and uphill gradients.
Different types of road gradient
There are different types of road gradients, which are as follows:
Average gradient
The average gradient refers to the ratio of total rise or fall to the horizontal distance among any two points along the road alignment. The average road gradient has been calculated by dividing the vertical differences among the two places along the road alignment by the horizontal separation.
Minimum gradient
The minimum road gradient has been used at those locations where the surface drainage is important. Slope is required for the smooth flow of the water in the case of the longitudinal drainage along with the side drains. The minimum gradient depends upon the soil types, the rainfall, and site conditions. In the case of the concrete drain, a minimum of 1 in 500 may be sufficient, whereas, in the case of the open soil drains, 1 in 200 is sufficient.
Limiting gradient
The limiting gradient has been adopted while the ruling gradient leads to the enormous increase in the construction cost. The adoption of the limiting gradient is necessary in the case of the hilly terrain and rolling terrain. The limiting gradient stretches strength should be limited. In addition, the limited gradient should be surrounded by the roads with less steep grades or straight roads.
Ruling gradient
This is the maximum gradient along with which the designer designs the vertical profile of the road. This type of road gradient has been adopted by the designers through considering the particular speed for a design vehicle along with standard dimensions. The ruling gradient depends upon the grade lengths, speed, terrain, vehicle’s pulling power and also the presence of the horizontal curve.
Exceptional gradient
These are the steeper gradients that have been given at unavoidable situations. The exceptional gradient has been limited for the short stretches and does not exceed about 100 metres at a stretch.
The exceptional gradient has been separated by a minimum 100 mitre length gradient in steep terrains and mountains.
To learn more, watch the following video tutorial.
Video Source: Gurukul of Civil Engineers
Floating gradient
The floating gradient refers to the road gradient on which a motor vehicle has been moved with a constant speed, which continues to descend with the same speed without any kind of power brake applications.
