Travel down an unpaved road can turn into a teeth-rattling, bumpy ride that might send a car spinning into the bar ditch. Narrow ridges that spring up from the surface of the road in a wavelike pattern, resembling the metal ribs of a washboard, are usually to blame. Until the early 1960s, the washboard effect was thought to be the result of “peculiar” soil, wind from passing vehicles, car exhaust, or impulses from car engines. Then geophysicist Keith Mather set up a homespun experiment to determine the cause. He attached a small wheel to the end of a strut and then set the strut in motion, like the hour hand of a clock, to mark a circular path in a bed of sand. Regular corrugations appeared. The faster he spun the wheel, the faster the washboard texture developed. The prerequisite was merely a dry, rough surface. When a tire hits a bump, dip, or rock in the road, it hops into the air and crashes down, spraying sand and gravel forward and sideways to form valleys. The moving tire hits the valley and hops again, repeating the process. The next car on the road only makes matters worse. Route 66, commissioned in 1926, was one long, dusty washboard road, crossing the country from Chicago to Santa Monica, until it was paved. Today, washboard roads are still found throughout the country, on every kind of bare ground.

Mary Swander