**Hi,**

If you have observed the pavement width on the horizontal curves, you will find that to be somewhat larger than the width on the straight roads.

*The pavement is extra widened on the horizontal curves due to the following reasons:*- The wheel base of the vehicles is rigid and therefore while taking the turn, only front wheel are able to change direction. Path traveled by the front will be different and will be at certain distance outwards from the path traced by the inner wheel. This can be understood with the help of the diagram and image shown below.
Extra widening on horizontal curves - There is a tendency of the driver to take the outer path at the curves to have more sight distance visible ahead.
- While overtaking operations on horizontal curves driver will need more spacing from the other vehicles to feel safer.

**Widening of the Pavement on the Horizontal Curves:**

Horizontal curve on a hilly road (Gocind Sagar view point-Himachal Pradesh) |

Widening of the pavement on the horizontal curves is governed by the following factors:

(a) Length of the wheel base

(b) Radius of the curve negotiated, R

(c) Psychological factor which depends upon the velocity of the vehicle and the Radius of the curve.

In general extra width is provided on the horizontal curves when the radius is less than 300 m.

Now,

Extra widening = mechanical Widening + Psychological Widening

IRC recmmended values for the Extra widening of pavement on Horizontal curves |

We = Wm + Wps

**We**=

**nl^2/ 2R**+

**V/ [9.5R^(1/2)]**

**Here,**n = number of traffic lanes

l = Length of the wheel base

V= Design speed in kmph

R = Radius of the horizontal curve in m

The figure given above shows the IRC recommended values of the extra width for the curves of different radius.

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