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Sleuthing the Source of Washboard Roads

While driving Alaska's graveled highways, countless people have no doubt wondered how an unpaved road surface turns into a bouncing bed of corduroy.

Keith Mather, former director of the Geophysical Institute and UAF vice chancellor for research, wondered the same thing, and in 1963 he published a paper on a subject near and dear to many Alaskans' shock absorbers--the formation of washboard roads.

Mather, who was studying nuclear physics in Australia in the early 1960s, wasn't satisfied with the theories of the time: that washboard roads were caused by "peculiar" soil, wind from passing vehicles, car exhaust, or impulses from car engines. He doubted all these possible causes because he noticed that many different surfaces, such as train tracks and ski trails, also can be afflicted with tiny roller coaster patterns.

Mather set up an inexpensive experiment at his lab in Melbourne. He assembled a contraption in which a tire connected to a central arm moved in a circle like the second hand moves on a clock. He covered the floor with sand and sent the wheel, which was about the size of a lawnmower roller, circling around the track.

He described the homespun project in his article: "We moved the wheel around the track by putting a finger behind the shaft and pushing it around the (track) to the beat of the family metronome. Greatly to my surprise this produced fairly regular little corrugations several inches apart in the sand." Mather found that washboard roads developed not only in sand, but also on "roads" of rice grains, sugar, and split peas. The key, he found, was that the surface was dry, as Alaska roads often are in the spring.

The faster he spun the wheel, the faster washboard appeared. With repeated passes of the wheel, he watched the road ripples multiply like snowshoe hares.

He noticed several keys to the formation of washboard roads: the road surface had to be non-rigid; the road had to be dry; and washboard tends to form just beyond an irregularity in the road surface, such as a bump, dip or small rock.

Bumps in the road surface cause the tire to hop in the air. When the tire crashes down, it forms valleys by spraying sand and gravel forward and sideways. The moving tire ramps out of the valley and hops again. Thus, the washboarding process repeats itself.

The washboard design spreads across the road when other cars repeat the action of the car that initiated it. Mather pointed out that bumps cause cars to react in the same way even though vehicles come in different weights and sizes, and with various suspension systems. He concluded, sadly, that other than slowing to about 5 miles per hour or using balloon tires to cushion the road, there isn't much drivers can do to prevent washboard roads from forming. Mather, who is now 74, retired, and living in Eugene, Oregon, said he still has heard of no solution.

At least for the time being, it looks like corrugated road surfaces will remain a literal pain in the neck, particularly in many developing countries, where major highways feature hundreds of miles of milkshake motorways.

Mather did note that some people, particularly Alaskans, view washboard roads with a certain amount of affection, however. He wrote that the bumpy stretches often are seen as "a welcome assurance of privacy in the outer reaches of suburbia."

And he did reflect with satisfaction on his study. He answered a question of worldwide significance with practical research--the total cost of his experimental equipment was $25.