Contents

# ExtraWidening:

Extra width provide to Road at horizontal curve is called extrawidening.

It is provided for following purposes:

• To avoid off tracking due to rigidity of wheel base.

• To encounter psychological tendency of driver.

• To increase visibility at curve.

• To account lateral skidding.

## Off tracking:

Path travelled by front axle and path travelled by rear axle it is not same on horizontal curve this phenomena is called off tracking.

# Extrawidening is split up into two parts.

1. Mechanical widening

2. Psychological widening

WE= WM+WP

WE= Extra widening

W=Mechanical widening

WP= Psychological widening

## (i) Mechanical widening:

Mechanical widening is provided to account off tracking.

R₁ = Radius of path traversed by the outer rear wheel (in m) wheel (in m)

R2 = Radius of path traversed by the outer front wheel (in m)

l = Length of wheel base (in m)

WM = Mechanical widening (in m)

$$R_2^{2}=R_1^{2}+l^{2}$$.

$$R_2^{2}=(R_2-W_M)^{2}+l^{2}$$.

$$R_2^{2}=R_2^{2}-2R_2W_M+W_M^{2}+l^{2}$$.

$$2R_2W_M-W_M^{2}=l^{2}$$.

$$W_M=\frac{l^{2}}{2R_2-W_M}≅\frac{l^{2}}{2R}$$. where, R= mean radius of curve.

$$W_M=\frac{l^{2}}{2R}$$.

$$W_M=\frac{nl^{2}}{2R}$$.

## (ii) Psychological widening:

There is a psychological tendency of driver to drive the vehicle close to the edge of pavement and maintain more side gap between the vehicle moving parallely.

$$W_P=\frac{V}{9.5\sqrt{R}}$$.

Where WP in m, R in m, V in KMPH.

WE= WM+WP

WE= $$\frac{nl^{2}}{2R}$$+$$\frac{V}{9.5\sqrt{R}}$$.(extra widening formula)

Note

IRC recommended value of extra widening for single and tow lane pavement are given below.

1. For single lane road Psychological widening =0.

2. If R> 300 m, then extra widèning is not provide.

3. If R< 50 m, then extra widèning is provided at inner edge.

4. If 50<R<300 m, then extra widèning is provided at both the edge.

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