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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One response to “Why Unpaved Roads Washboard”

  1. Kyle Memoir 🍉 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.

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