What causes the even pattern of ripples in a “washboard” gravel road?

Question

I finally stopped to look more closely. These ripples are about 10 inches wide ands look to be almost exactly uniform through long stretches of road. Where does this precision come from?

In: 879

Answer 1

It’s caused by tires slipping on the slick dirt surface, or in areas where cars accelerate such as after a tight corner or up a steep hill. Unfortunately I really doubt you’ll ever get people to understand this.