It has long been policy on the Mauna Kea summit road to use four wheel drive while ascending the mountain. One of the reasons given is to slow the formation of washboard, the annoying ripples that inevitably form on gravel roads.
On Mauna Kea an oft cited mantra is that the use of four wheel drive when ascending the mountain reduces the formation of washboard. I have always suspected this is a mountain myth with no substance. Where does this belief come from? Is there any real information on this?
The Manuals
There are a great many references that detail the practical details of maintaining gravel roads. Generations of highway engineers have spent a lot of time studying and writing about how to best maintain gravel roads at the least cost.
The US Department of Transportation highway Administration has published a lengthy guide to the problems and solutions of gravel roads. This guide dedicates a dozen pages to the issue of corrugation or washboarding. While multiple factors in the formation and prevention of washboarding are discussed there is no mention of 4WD vehicles being a factor.