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INTERCHANGE

Interchange
This system whereby facilities are provided for movement of traffic between two or more roadways at different levels in the grade separation.
A structure without interchange is an over-bridge or underpass flyover, whereby the traffic at different levels moves separately without a provision for an interchange between them
  
The interchanges can be classified as three-leg, four-leg and multi-leg, and these can be subdivided into various types as below:

A.    Three –leg interchange
1.     T-interchange
2.     Y-interchange
3.     Rotary interchange

B.   Four-leg interchange
1.     Diamond interchange
2.     Half clover leaf interchange
3.     Clover leaf interchange
4.     Rotary interchange
5.     Directional interchange

C.   Multi-Leg Interchange
1.     Rotary interchange

Types of rotary interchange (Round about) based on shape

i.                     Circular Rotary
ii.                   Rectangular With Round Edges
iii.                  Square with Rounded Edges
iv.                 Irregular
v.                   Elliptical


The advantages of intersection

i.                     An orderly and regimented traffic flow is provided by one way movement
ii.                   All traffic proceeds simultaneously and continuously at fairly uniform, though slow speed. Frequent stopping and starting are avoided
iii.                  All turns can be made with ease, although little extra distance is required for all movements except left turns.
iv.                 For moderate traffic, rotaries are self-governing and need no control by police or traffic signals

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