I've been aware of “traffic waves” for several years now and the animated graphics on the site do illustrate the issue, but now it seems that Japanese researches have actually created “traffic waves” on a closed course:
Researchers from several Japanese universities managed the feat by putting 22 vehicles on a 230-metre single-lane circuit (see video).
They asked drivers to cruise steadily at 30 kilometres per hour, and at first the traffic moved freely. But small fluctuations soon appeared in distances between cars, breaking down the free flow, until finally a cluster of several vehicles was forced to stop completely for a moment.
That cluster spread backwards through the traffic like a shockwave. Every time a vehicle at the front of the cluster was able to escape at up to 40 km/h, another vehicle joined the back of the jam.
The shockwave jam travelled backwards through the ring of vehicles at roughly 20 km/h, which is the same as the speed of the shockwave jams observed on roads in real life, says lead researcher Yuki Sugiyama, a physicist in the department of complex systems at Nagoya University.
The video of the “traffic waves” (called “shockwave traffice jams” in the video) is fascinating to watch as the “traffic wave” just kind of happens.