Railway tracks are banked on curves so that :

A vehicle moving at a fast speed on a straight

rail/road has a large inertia, i.e. tendency to

keep moving in the same direction at the same

speed. When it takes a circular turn on a

curved rail/road, it experiences an additional

force, termed as centripetal force, acting towards the centre of the circle. While rounding

the curve as the vehicle has tendency to leave

curved path and regain straight line path, force

of friction between wheels and ground provides

necessary centripetal force. In order that the

vehicle can go round the curved track at a reasonable speed without skidding, the sufficient

centripetal force is managed for it by banking

the rail/road