Washboard Roads

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. The wheel climbs out of this irregularity and, thereby, again flies into the air. Thus, a single irregularity leads to the formation of others evenly spaced down the roadway at locations dependent upon the weight and springing of the vehicle and its speed. Other wheels on other cars coming along behind repeat the process, causing the unevenness of the road surface to increase and spread across the full width of the roadway. On a particular stretch of roadway, vehicles tend to travel at about the same speed and, despite their differences, they bounce about the same, so their collective action is to increase rather than smooth out the bumpiness.

Interestingly enough, it doesn't matter whether a wheel is driven by a powered axle or spins freely on an axle, its tendency to create corrugations is the same. About the only way to prevent the buildup of washboard surfaces is to drive slowly, very slowly, perhaps less than 5 or 10 mph.