The extra widening refers to provide extra width of carriageway on the curve portion of the road. They are two types, one is mechanical widening and another one is psychological widening.
Method of Providing Extra Widening
⇰The widening is provided starting from the beginning of the transition curve and gradually expanded at a uniform rate, till the full value of designed widening ‘W’ is given at the end of transition curve where full values of superelevation are also provided.
⇰Then the full value of extra width W is continued throughout the length of the circular curve, after that, it starts to decrease gradually along the length of transition curve.
✅Now we will try to understand it by seeing the picture(Fig.1)
For the left sides portion of the road, ‘A’ is the starting point of the transition curve, and ‘B’ is the end-point of the transition curve and also starting point of the circular curve.
For the right sides portion of the road, ‘C’ is the starting point of the transition curve, and ‘D’ is the end-point and starting point of the transition curve and circular curve respectively.
Now, we are providing extra widening starting from point ‘A’, and its value is increased gradually up to the point of B, and It gets its full value at point ‘B’. Then the full value of extra widening(W) is constantly provided up to the point of C, after that the widening value is gradually decreased up to the point of D, and finally, it should be zero at point D.
⇰ Usually, the extra widening(W) is provided equally both on the inner and outer sides of the curve, i.e W/2 for each side of the curve road. But sometimes the extra widening (W) may be provided in full on inner sides of the curve(example: For sharp curves of hill roads)
⇰ For without transition curve roads, two-thirds the widening is provided starting from the beginning of the circular curve and the remaining one.