DESIGN OF HORIZONTAL ALIGNMENT

HORIZONTAL ALIGNMENT: 

Horizontal alignment design involves the understanding on the design aspects such as design speed and the effect of horizontal curve on the vehicles. The horizontal curve design elements include design of super elevation, extra widening at horizontal curves, design of transition curve, and set back distance.

They are of 4 types :

1. Left aligned

2. Right aligned 

3. Centered

4. Justified 

HORIZONTAL CURVE DESIGN ELEMENTS: 

1. Design of super elevation

2. Extra widening at horizontal curve. 

3. Design of transition curve

4. Design of set back distances

1.Design of Super elevation : 

Superelevation is the banking of highway horizontal curves to assist the driver by counteracting the lateral acceleration produced by tracking the curve. Superelevation is expressed as a decimal, representing the ratio of the pavement slope to width, and ranging from 0.04 to 0.12.

2. Extra widening at horizontal curves:

When a vehicle takes a turn to negotiate a horizontal curve, the rear wheels do not follow the same path as that of the front wheels. ... To compensate this, the carriageway width increased on the entire curved portion of the road, which is called extra widening of pavement on curve.

3. Design of transition curve: 

A track transition curve, or spiral easement, is a mathematically-calculated curve on a section of highway, or railroad track, in which a straight section changes into a curve. It is designed to prevent sudden changes in lateral (or centripetal) acceleration.

4. Design of set back distances: 

Setback distance m or the clearance distance is the distance required from the centerline of a horizontal curve to an obstruction on the inner side of the curve to provide adequate sight distance at a horizontal curve. The setback distance depends on. 

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