CURVES

CURVES

CURVES

Curves

The curves are provided on highway to change the direction either horizontal or vertical plane in gradual way.
The necessity of providing curve arises due to the following reasons:

1)Topography of the country
2)To provide access to a particular locality
3)Restriction imposed by some un avoidable reasons of land
4)Preservation of existing amenities
5)Making use of existing right of way

The various factors which affect the design of curve are as follows:

1)Design speed of vehicle
2)Allowable friction
3)Maximum super elevation

Classification of Road CurvesThe curves are divided into two classes

v  Horizontal Curve

Horizontal curves are simple, compound and reverse curves. A curve which consist of a single arc connecting two straights is called a simple curve, a curve which consist of a series of two or more than two simple curve that tern in the same direction is called as compound curve, a curve consist of two simple curve of opposite direction is known as compound curve.

v  Vertical Curve

Following are two types of vertical curves:

• Summit curve
• Valley curve

Summit curve	Valley curve
A vertical curve with convexity upward is called summit curve, the major factor in the design of summit curve is sight distance, summit curve are required to be introduced at the situation where:	A vertical curve with convexity downward is called a valley curves. These are required to introduced at the situation where:
i. A positive grade meets a negative grade	i.A negative grade meets a positive grade
ii.A positive grade meets another milder positive grade	A negative grade meets another milder negative grade
iii.A positive grade meets a level surface	ii.A negative grade meets a level surface
iv.A positive grade meets a steeper positive grade	iii.A negative grade meets a steeper negative grade