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 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 s, 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. The key, he found, was that the surface was dry, as Alaska roads often are in the spring. On a soft surface like a dirt road, the push back either packs or displaces the dirt it hits. Over time, as more and more cars go over the bump, the washboard pattern develops.
However, in the summer of , physicists from Canada, France and the United Kingdom published a new study about the physics of washboard road formation. They discovered that ripples will form, even when the springy suspension of a car and the rolling shape of a wheel are eliminated [source: American Physical Society ].
They built an experimental vehicle, replacing the wheel with a suspension rolling over a road with a simple inclined plow blade, without any spring or suspension, dragging over a bed of dry sand. Ripples appear when the plow moves above a certain speed. After observing the results, they compared this phenomenon to the physics of stone skipping: A stone needs to be thrown above a specific speed in order to have enough force to bounce of the surface.
A washboarding plow is similar, except the sandy surface remembers its shape and the effect is amplified. They concluded that the formation of a washboard pattern is inevitable. The ridges will form, even if the wheel diameter, suspension or surface is changed.
The only way to avoid the effects of a washboard road is to stay below a certain speed, but that's impractical: you'd usually have to drive at 3 miles per hour 4. Some day, such discoveries may lead to improved suspension systems or improved road surfaces that smooth out a bumpy ride.
In the meantime, there's not much you can do about washboard road except brace yourself, watch your speed and hang on for the ride.
While washboard roads can occur anywhere, they are most often seen in hot, dry areas and on sandy, dirt or gravel roads. What causes washboarding to be worse in some locations than others?
There are three main causes:. If you travel dirt roads frequently, you know that you can find an ideal speed that will help smooth out the ride. That's the speed at which your car's suspension system is pushing the car down at the same time you experience a dip in the road. You may think that because you have large, wide tires you have unlimited traction.
No so. Just like with snow, gravel offers serious challenges, especially at higher speeds. Inspect your vehicle before and after the trip for any loose parts, especially relating to the suspension system. Slow down. Wait until you are moving very slowly before you steer back onto the roadway.
Most people drive right down the middle of the gravel roads. That means on coming traffic is right in the middle of the road too. Be alert for oncoming traffic and other hazards. Get over to your side of the road as you approach a curve or hill. A trip out in the country can be one of the more enjoyable ways to spend an afternoon. Knowing how to drive on unpaved roads will help keep it that way. Nice info on the wash boarding effect. I have usually picked up the speed to help minimize the effect or tried to find a smoother spot in the road.
But how does washboard become whoop-de-doos? And how come the ridges go all the way across the road in a fairly straight line? How does the right end know what the left end is doing?
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