Question

Why curved roads are banked

Answer 1

Assuming that if a person is driving a car and there is a curved surface where he have to drive his car ? At that place he wants a banked road because 
on the banked roads when we rotate a car handle so there is a centripetal force which is acting to our body and tries to put out from our car. so roads
are banked to balance centripetal force with mg.

Answer 2

In order to negotiate the curve properly to avoid skidding. By banking the road, we take advantage of the component of weight and friction acting along the centre of the curve.