Scientists in Japan have succeeded for the first time in experimentally reproducing traffic jams. You can read about it here or you can read about it here (both articles say basically the same thing).
You can also see a video of the experiment on YouTube. It is pretty interesting, but I wish they had done more work to figure out how many cars it takes to cause a traffic jam. Clearly, two or three cars on the track wouldn’t produce a shockwave. Ten cars might produce one but it would take longer, for example. Then maybe they could come up with a general equation to predict the capacity of a section of road.
