What is the main reason roads are tilted on curves, helping cars stay stable?

The main reason roads are tilted on curves, a design practice known as banking, is to provide the necessary centripetal force that keeps a car moving in a circular path and prevents it from skidding outwards. When a car travels around a curve, its inertia, which is the tendency of an object to resist changes in its state of motion, makes it want to continue moving in a straight line. To force the car to follow the curved path, a net force must act upon it, pointing towards the center of the curve; this required force is called centripetal force. On a flat curve, the entire centripetal force must be supplied by the friction between the tires and the road. However, friction has limits based on tire condition, road surface, and speed, and can become insufficient, especially at higher speeds or in adverse conditions like rain, leading to a loss of traction and the car skidding off the curve. Banking the road means tilting the surface, so one side of the road is higher than the other. When a car is on a banked curve, the normal force, which is the force exerted by the road perpendicular to its surface, is no longer purely vertical. Instead, this tilted normal force has a horizontal component that points directly towards the center of the curve. This horizontal component of the normal force directly provides a significant portion, or even all, of the required centripetal force. By utilizing this component of the normal force, the banked road effectively pushes the car into the turn, greatly reducing the reliance on friction to provide the centripetal force. This design enhances stability, allowing vehicles to safely navigate curves at higher speeds and preventing them from sliding outwards due to insufficient centripetal force.