Back roads in Australia often have hundreds of metres of gravel corrugations, or ridges. They are always a few centimetres high, spaced about 30 centimetres apart… and annoying for vehicle occupants. What causes them?
• When a vehicle is driven over an unsurfaced road, its weight indents the material under the tyre. The loose particles ahead of the tyre tend to be pushed forwards, creating a small ridge.
Each passing vehicle gradually raises the ridge, until the rate of material removal from the crest due to abrasion and impact stop it getting any taller. The maximum height of the ridge depends…
