The Math of a Traffic Jam

Ok, every one has been in one. The traffic seems backed up for miles and you poke along, and then, suddenly you are moving again. No dead bodies on the side of the road, no carnage, no accident at all, and yet.... the traffic almost at a standstill.
For years mathematicians and computer geeks have simulated these "schockwave" traffic jams, but now a team of Japenese researchers have created a physical example. They put a bunch of cars, 230 to be exact, on a circular track, and told them to drive at a steady 30 mph. At first it all seemed to go well, but then, those tiny variations in speed caused some grouping up... somebody touched a brake and then... well just watch the video....