Types of curves found in hill road
The following types of curves are mostly found on hill Roads:-
1. Hair-Pin Curves ;
2. Salient Curves ;
3. Re-entrant Curves.
1. Hair-pin curves: This type of curve modifies its direction via an angle of 180 degree down the hill on the similar side is defined as hair-pin curve.
A Hair-Pin Bend: This curve is known as a hair-pin bend since it adheres to the shape of a hair-pin. If a bend is developed at the hair-pin curve in a hill road, it is called as hair-pin bend.
This type of curve should have been situated on a hill side containing the lowest slope and highest strength. It is considered as very secure from view point of land slides and ground water. The ideal Hair-pin bends should contain long arms and farther spacing. They minimize construction issues and high-priced protective works.
Hair-pin curves or bends with snakelike form are difficult to arrange and as a result they should not be recommended at all.
2. Salient curves: The curves which contain their convexity on the exterior edges of a hill road are defined as salient curves.
The centre of curvature of a salient curve is located towards the hill side. This type of curve appears in the road length that is built up on the ridge of a hill. The bend that is developed at the salient curve in a hill road is called corner bend.
Salient curves are very harmful for the traffic moving speedily. At such a curve or at corner bend, the segment of projected hill side is normally curtailed to make the perceptibility better.
It is demonstrated in the following figure (re-entrant curve). In the exterior perimeter of the road, the curve is basically arranged with a parapet wall for safeguarding the vehicles from falling down the hill slope.
3. Re-entrant curves: The curves which contain their convexity on the inside edge of a hill road are known re-entrant curves.
The centre of curvature of re-entrant curves is located ahead of the hill side. This type of curve appears in the road length that is built up in the valley of a hill.
These curves are not harmful since they offer sufficient visibility to the traffic moving speedily. In such curves, the parapet wall is arranged only for protection for fast moving traffic.