Curve:

Curves are provided in highways in order that the change of direction at the intersection of straight alignments either in horizontal or vertical plane, shall be gradual.

Note: This topic is part of the second chapter of Highway Engineering. I suggest reading this topic in the context of the complete chapter: Geometric Design of Highway. If you want to read the entire Highway Engineering, click here: Highway Engineering.

The necessity of curves arises due to the following reasons:

1. Topography of the country
2. To provide access to a particular locality
3. Restrictions imposed by property
4. Preservation of existing amenities
5. Avoidance of existing religious, monumental and other costly structures
6. Making use of existing right of way

Advantages of Curves

The advantages of providing curves are:

1. They provide comfort to the passengers. If there is an abrupt change in the direction nor grade of a highway it will upset the passengers.
2. They help to avoid mental strain induced by the monotony of continuous journey along straight path.
3. In the case of sharp turns, brakes have to be applied more frequently which reduces the life of tyres. Thus life of the vehicles in increased by providing curves.
4. The drivers became alert due to the change in the direction of road.
5. They help to keep the speed of the vehicle within limits. On a straight road, a driver is tempted to go at a much faster speed.

Factor Affecting the Design of Curves

The various factors which affect the design of curves are:

1. Design speed of the vehicle
2. Maximum permissible superelevation
3. Allowable friction
4. Permissible centrifugal ratio

Type of Curves

Curves have been divided into two classes:

(1) Horizontal Curve: A curve in plan to provide change in direction of the central line of a road.

(ii) Vertical Curve: A curve in the longitudinal section of a roadway to provide for easy change of gradient.

The different types of curves used in highways are:

(i) Simple Circular Curve: A simple cùrve consists of a single are connecting two straights.

(ii) Compound Curve: A compound cùrve consists of a series of two or more simple curves that turn in the same direction and join at common tangent points.

(iii) Reverse Curve: A reverse cúrve consists of two simple curves of opposite direction that join at the common tangent point called the point of reverse curve.

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