Curve :
Road curves are irregular bends in roads to bring a graduation change of direction, this are provided in highways or roads that the change of direction at the intersection of straight alignment either in horizontal or vertical plane, shall be gradual.
Due to the conditions like topography, preservation of existing properties, provide access to a particular locality etc., curve is provided.
Factors Affecting the Design of Curves :
- Design Speed
- Allowable Friction
- Permissible Centrifugal Ratio
- Maximum Permissible Super-elevation
Main type of Curves :
- Horizontal Curve
- Vertical Curve
Horizontal Curve :
Curves provided in the horizontal plane are known as horizontal curves or a curve in plane to provide change in direction of the center line of a road, and generally these curves are circular or parabolic.
Types of Horizontal Curves :
- Simple Circular Curve
- Compound Curve
- Reverse Curve
- Deviation Curve
Simple Circular Curve :
A simple curve has the same radius throughout and is a single arc of a circle, with two tangents meeting at the intersection.
Simple Circular Curve
Compound Curve :
A compound curve has two or more simple curves with different radii that bend the same way and are on the same side of a common tangent.
Compound Curve
Reverse Curve :
Also called a serpentine curve, it is the reverse of a compound curve, and two simple curves bent in opposite directions are on opposite sides of the common tangent.
Reverse Curve
Deviation Curve :
A deviation curve is simply a combination of two reverse curves. It is used when it is necessary to deviate from a given straight path to avoid intervening obstructions such as a building, a body of water, or other significant site.Vertical Curve :
Curves provided in the vertical plane are known as vertical curve or a curve in the longitudinal section of roadway to provide for easy change of gradient.
Type of Vertical Curve :
- Valley Curve
- Summit Curve
Valley Curve :
Also called a sag curve, this curve dips down and then rises back up. These are placed in the base of hills. The opposite of summit curve. A valley curve is vertical curve with concavity upward or convexity downward.
Valley Curve
Summit Curve :
Also called the crest curve, this cure rises and then dips down. At the peak of hills. The opposite of valley curve.
Summit Curve
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