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The widening of a road is not required when its radius will be
less than 300 m
more than 300 m
less than 460 m
more than 460 m
more than 460 m
According to the Indian Roads Congress (IRC) guidelines, extra widening of a road is provided on horizontal curves to account for off-tracking of vehicles and psychological widening. When the radius of the curve (R) is greater than 460 m, the calculated extra widening is generally negligible (less than 0.1 m), and thus it is practically ignored.
According to the Indian Roads Congress (IRC) guidelines, extra widening of a road is provided on horizontal curves to account for off-tracking of vehicles and psychological widening. When the radius of the curve (R) is greater than 460 m, the calculated extra widening is generally negligible (less than 0.1 m), and thus it is practically ignored.
WmтАЛ=2Rnl2тАЛ тАФ Mechanical widening for off-tracking
WpsтАЛ=9.5RтАЛvтАЛ тАФ Psychological widening
WeтАЛ=2Rnl2тАЛ+9.5RтАЛvтАЛ тАФ Total extra widening
Widening consists of two parts: mechanical widening (WmтАЛ) to compensate for the off-tracking of long-wheelbase vehicles, and psychological widening (WpsтАЛ) to provide a sense of safety for drivers negotiating the curve. The total widening is given by WeтАЛ=WmтАЛ+WpsтАЛ=2Rnl2тАЛ+9.5RтАЛvтАЛ. As R increases, the denominator increases, causing both components to decrease toward zero.
Widening is mandatory when R<300 m.
Widening is optional or negligible when R is between 300 m and 460 m.
Widening is not required when R>460 m.
Off-tracking occurs because the rear wheels follow a shorter path than the front wheels on a curve.
Increases safety for overtaking on curves
Prevents structural damage to road edges
Higher initial construction cost
Increases land acquisition requirement
Highway geometric design
Design of mountain roads with tight curves
The value 460 m is derived based on the standard wheelbase of the design vehicle and speed characteristics specified in IRC:73.
Option C (<460 m) is incorrect because it describes the range where widening is typically still recommended.
D is correct тАФ According to IRC standards, the extra widening requirement becomes negligible for horizontal curves with a radius exceeding 460 m.
Always remember the threshold values: R<300 m (Must provide), 300<R<460 m (Optional), R>460 m (Not required).