Corrugations

This section of estate track near our house is displaying a phenomenon with which drivers in countries where dirt roads are common are only too familiar. Corrugations are like ripples in sand, usually with a wavelength of about a metre and an amplitude of 25-50mm, which develop across the road. They're formed by the passage of vehicles along a road which has an unconsolidated sandy or gravelly surface, the corrugations being formed when the wheels start to bounce along the road.

Travelling along such roads is both uncomfortable and jarringly painful, particularly as corrugations can continue for many miles. That they have formed on this estate track is a bit of a mystery - it's the first time I've seen corrugations outside Africa. The juddering has other, sometimes dangerous effects. For example, phillips screws have a habit of falling out.

We found that it was agony to travel along such roads slowly, and that the best approach was to drive as fast as possible so the car planed across the corrugated surface. When the car did this, it lacked traction, which meant that, in inexperienced hands, there was an increased chance of an accident. 

Corrugations were just one of the many trials of travelling on African roads. In the wet season these surfaces were sometimes covered with a slick of mud, which meant the surface behaved rather like the black ice of UK roads. Add to these problems the hazards of clouds of dust in the dry season, the way loose sand also acted like black ice, and deep, glutinous mud in the wet, into which cars sank axle-deep. Little wonder that African roads exacted a high price in human lives.