Washboard road results from the instability of a granular surface under the action of rolling wheels. Here, a hard rubber wheel rolls on the edge of a rotating table covered with a bed of sand. The wheel suspension is simply a lever. The table is 1.2 m in diameter.
The movie shows the onset of the ripple pattern, which appears as a very small patch of bumps after a while. The movie is in slow motion.
Here are two more movies of a long view of the experiment, and of the fully developed ripple pattern.
Go here for downloadable versions of the movies in other formats.
See Washboard Road abstract for a publications about this effect.