• Extra widening (W_e) refers to the additional width of carriageway that is required on a curved section of a road over and above that required on a straight alignment. This widening is done due to two reasons: the first one is the additional width required for a vehicle taking a horizontal curve. This is called mechanical widening (W_m), as it is due to the rigidity of the wheelbase, and the second is due to the tendency of the drivers to ply away from the edge of the carriageway as they drive on a curve. This is called psychological widening (W_ps).

 

• Mathematically, extra-widening is given by the formula using two methods:

1. Based on the rate of change of centrifugal acceleration