Types of Curves

For the comfort and ease of drivers, there are several types of curves are provided in the road which plays an important role in the geometric design of road and railway alignment.

Therefore, it must be properly studied and designed, so that safety, comfort and convenience can be provided or accidents can be reduced while driving vehicles.

Curves are regular bends provided in the lines of communication like roads, railways, and canals to bring about a gradual change of direction.

They enable the vehicle to pass from one path to another when the two paths meet at an angle, curves provided within the vertical plane at all changes of grade to avoid the abrupt change of grade on the apex.

Necessity of different curves:

  • Excessive cutting or filling can be prevented by providing the change in alignment by the curve.
  • The obstruction like natural or artificial which comes in the way of straight alignment can be made easier in providing the by-pass with the help of curves.
  • Within the straight route, gradients are made extra comfortable and easy by offering diversions with the help of curves.
  • In a straight route, if costly land comes in the way, then it can be avoided by providing diversions with the help of curves.
  • Track or road is made the stable and safe, side of the hill by changing the alignment.

Different types of curves:

A) Horizontal Curves:

The horizontal curves achieve a gradual change in the directions provided at a bend or turn.

In railway tracks, the minimum radius of a horizontal curve for broad gauge should be 175 meters.

In the case of horizontal as well as vertical, road curves should ensure safety, comfort, and convenience for traffic, while they are further classified as follows:

1.Simple Curve:

A curve in which there is an arc of a circle with two straight tangents join and bring a deflection of the road through an angle is called a simple curve.

The simple curve is normally represented by the length of its radius or the degree of the curve.

These types of curves are provided at every change in the alignment of a road or railway track in a plain and hilly area.

2.Compound Curve:

A curve with a series of two more simple curves of different radii in the same direction is called a compound curve.

In the compound curve, the two adjoining curves may have a common tangent and the centers of the two adjoining curves might be positioned on the identical side of the curve.

In order to avoid erosion through hard rocks, heavy cutting or filling in the alignment of the road or track the mixed curves are provided.

3.Reverse curve:

The curve which consists of two simple curves, which are equal or different rad in the opposite direction, is called reverse curve.

The two centers of the curves are on opposite sides of a common tangent.

Reverse turning is required on mountainous routes, where frequent changes in the direction of travel and the alignment of railway tracks in station yards and hilly areas.

4.Transition curve:

A curve in which the radius gradually varies from infinity to a finite value that is equal to a circular curve and vice versa is called the transition curve.

These curves are commonly used in railway tracks between circular curves and tangents to provide an easy and gradual change in direction.

This provides a gradual change in the radius of curvature.

In addition, it provides smooth entry of the vehicle from the straight part to the curved part to allow the gradual application of overgrowth and widening on horizontal curves.

b) Vertical curves:

The curves provided in the alignment of the road or track at the time of gradient change are called vertical curves which provide adequate visibility and security to the traffic.

These curves gives a gradual change in grade or slope that provides a sufficient comfort to the passengers.

1.Summit Curve:

The curves which are having convex surface on upward side is termed as summit curve.

2.Valley Curve:

Curves with convex surface at the bottom are called valley curve.

Functions of various types of Curves in Roads:

  • A gradual change in gradient in alignment can be done by providing curves.
  • Also, gradual change in direction or orientation in the alignment can be made by providing curves.
  • Curves have been provided to provide comfort to the passengers.
  • The curves have been provided for easy diversion in terms of road and track.
Also read: Types of Roads, Types of pipes & Types of Bridges


The various types of curves are continuous and smooth flowing lines without any sharp turn while recognizing the curve that it bends makes changes its direction at least once.

Hello, I'm Rahul Patil founder of Constructionor.com, I had studied B.E. Civil. This blog provides authentic information regarding civil structures, equipment, materials, tests & much more.

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