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. Thus, water increases particle movement, and corrugation formation and depth. Lower vehicle speeds will help prevent washboarding. They will also reduce acceleration and deceleration, and their adverse affects. Most drivers on a gravel road live on it.