Driving on a dirt road can rattle the bones. Every foot or so, a ridge of dirt up to several inches high lies in wait to jolt passing cars and trucks and their hapless occupants. In many places, road crews battle this "washboard" effect by frequently scraping the roads with bulldozers. But as soon as more vehicles pass, the ridges, phoenixlike, return.
Now, a team of physicists has explained why a washboard forms, and their research has a dispiriting message for road crews: Scrape often, or give up. Washboard is inevitable.
Most previous theories of washboard formation involved relatively complex dynamics. Some focused on the bounce of a vehicle's suspension and tires. Others suggested that differences in compaction between the