Washboard roads are a familiar part of the northern scene, just as they are in all parts of the world where people travel over unsurfaced roadways. Actually, corrugations develop on surfaced roads, too, as well as on steel or other hard surfaces upon which wheels roll, though the corrugations there are not so noticeable. For many years people have speculated, usually wrongly, about the exact cause of road corrugations. The real answer comes from a series of experiments and observations conducted in Australia nearly 20 years ago by Dr. Keith B. Mather, now vice chancellor for research and advanced study at the University of Alaska. The lurid details are given in an article by him that appeared in Scientific American, Volume 208, published in 1963.
Corrugations develop most easily on dry, dusty roads.
The corrugations start to develop at a point where a rolling wheel strikes an irregularity on the road surface. The irregularity might be a dip, a bump or even a small rock. This irregularity causes the wheel to fly upward above the roadway. A short distance beyond the irregularity the wheel impacts the ground again. Where the wheel lands, it tends to dig in to create another irregularity.