Why Unpaved Roads Washboard

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As anyone who has regularly traveled unpaved roads knows, they have a tendency to develop regularly spaced corrugations, otherwise known as washboarding. In addition to shaking cars and passengers, these uneven surfaces make cars harder to control, sicne the wheels can lose contact with the ground entirely at times.

Unfortunately, this phenomenon is fairly unavoidable. Once you have a wheel moving across a granular surface above a critical speed, you get these self-reinforcing patterns. It’s similar to the way that tidal ripples and sand dunes form, and it’s how you get moguls on a ski run, too!

Although they’re somewhat inevitable, as Grady describes, engineers are hard at work figuring out how to keep them from forming too quickly. (Video and image credit: Practical Engineering; research credit: N. Taberlet et al. and I. Hewitt et al.)

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4 responses to “Why Unpaved Roads Washboard”

  1. James Gilbert Avatar

    @admin Braking bumps on mountain bike trails too!

  2. Kyle Memoir πŸ‰ Avatar

    @admin

    Having cycled a lot of gravel these last few years, I can throw in that I see these mostly in acceleration and deceleration zones, where tire/surface forces are highest.

    Paving or otherwise hardening these zones would go a long way to reducing the problem.

    Another factor is drainage: where water collects or soaks a soft surface, some of it gets expelled under pressure (carrying road material with it) with each vehicle's passage. Corduroy & pothole growth are both accelerated this way.

  3. David Croyle Avatar

    @admin I'd love it if they came up with a simple, practical solution to solve this effect, which can not only be a miserable experience but also damaging to vehicles.

    There's like a 25-mile(?) stretch of washboard that forms on Racetrack Road in Death Valley that's pretty brutal, but I hear that the Aussie outback has much longer sections of it.

  4. Nantucket Lit Avatar

    @admin Washboarding made for a great scene in the movie The Wages of Fear. Two trucks are hauling nitroglycerin through the jungle. The first truck decides to go very slow over the washboard road. The second truck, quite a ways behind, decides to floor it and glide over the washboard. It sets up one of the high points of suspense in cinema.

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