What is Gradient in Highway - vertical Alignment of highway-Types of Camber and and Formula for Providing camber

Gradient, the rate of rise and fall of a highway surface along the length of the highway is termed as gradient. It is usually expressed as a ratio of 1vertical in n horizontal. For example if a highway surface falla in 4m in a horizontal distance of 200m measured along the length of the highway, the highway gradient is 1 in 50.sometimes is alost expressd as percentage. 

Gradient

Types of gradient:
1) Maximum gradient
2) Ruling gradient
3) Minimum gradient
4) Exceptional gradient

Maximum gradient in plain area is 1 in 20 and hilly area 1 in 15
Ruling gradient in plain 1 in 30 and in case hilly 1 in 20
In case Exceptional gradient, 1 in 15 in plain and 1 in 12 in hilly areas.


What is Vertical Alignment of Highways

The vertical alignment of highway generally defined as the presence of  depths and height in vertical axis with respect to horizontal axis of alignment. These depths and heights in roads may be in the form of gradients (straight lines in a vertical plane) or vertical curves.

What is Ruling Gradient

This is the Ruling gradient which is generally used to design the vertical profile of highway. So it is also called as designer gradient. Ruling gradient depends on the terrain, speed,lenght of grade pulling power of the vehicle and the presence of the horizontal curve. It is adopted by considering a particular speed as the design speed and for a design vehicle with standard dimensions of roads. In flat terrains roads it is possible to provide flat gradients and in hilly terrains it is very costly and sometimes it is difficult to provide ruling gradient in hilly terrains.

What is Limiting Gradient

This type of gradient is provided as shorter stretches in highways. Whenever ruling gradients costs high for the hilly terrains roads then the limiting gradient is provided which will reduce the cost of road project. This type gradient is adopted frequently in terrains road with limited stretches.

What is Exceptional Gradient

These are very steeper gradient given at unavoidable situations and they are adopted for stretches not exceeding 100meter in length

What is Minimum Gradient

Minimum gradient is needed to drain of rain water from the road. Generally for lateral drainage Camber is provided. But for the longitudinal drainage along with the side drains required some slope for smooth flow of water. For concrete drains minimum gradient of 1 in 500 and in case open soil drains gradient of 1 in 200 is suitable.

Vertical Curves

Generally there are two types of vertical curves are there to adopt for the vertical alignment. They are two types:-

• Summit curve
• Valley curve 

Summit Curve

when the gradient is upwards then summit curve is  adopted mainly. In case of summit curve simple parabola is considered as per curve shape. There are four different cases are involved in summit curve as follows.

Valley Curve

 when the gradient is downwards then vertical curve is provided. Generally  the vehicle meets downward gradient it discomfort arises and accelerates more . So, in the design of valley curve consider the comfert in vertical alignment d along with sight distance. Here also four cases are considered but case two and case three are same as summit curve