This kind of annoying phenomenon occurs on roads with a steady traffic flow if the distances between cars become too small: As soon as a car slows down a bit for whatever reason, the following car must break also, and so on. And because drivers are humans and have a reaction time, they break ever later, and ever stronger, and at one point, they come to a full stop. This stop then moves "upstream", in the opposite direction of the traffic flow - it's a shockwave-like phenomenon that has been intensively studied by German physicists since the 1990s.

Type A asshole "I gotta be first" drivers are the primary causes of this phenom.

DMT

One can see how a perturbation of the steady flow set in after just 40 seconds around metre 150 of the track. At closer inpection, the culprit seems to be a car that was a bit slower than the others for a while.

North of Portland OR there are some big iron Jesus statues that always had a traffic jam around them when I driving to/from Hood River from Vancouver BC. Now that they've been there for a few years and people are mostly used to them the traffic jams seem to have subsided. The video experiment seems to support my theory that the statues were to blame.

There's even a video of an experiment on a circular track to show this:
http://backreaction.blogspot.com/...al-traffic-jams.html

You're probably right. The really big one, though, is people slowing down to rubberneck when going past the scene of an accident.

I think George Carlin summed it up best:
"When your driving, anybody in front of you is a moron, and anybody passing you is insane."