In addition, continuing traffic begins to move the stones into the pattern of ridges and valleys. The force of the tires and the road surface, The motion of vehicles bouncing ups and down on their springs and tires. The degree of damage depends on tire hardness and vehicle acceleration, deceleration, turning, and speed. Because hard tires excerpt greater force per square inch on the road surface, they break and scatter aggregate more than do soft tires. Therefore, corrugations usually occur first at road and driveway intersections, and at tops and bottoms of hills.
High speeds increase both tire force and bouncing.
Fast moving vehicles, therefore, quicken the formation of corrugations and increase their depth. These factors have the greatest effect on roads with a weak base, poor drainage, or both. A weak base deflects under loads, and becomes deformed into the same wave-like pattern as the surface. Poor drainage leaves water in the road, or allows it to percolate in from the sides. Too much water lubricates the base and surface particles.