The latest issue of Atlantic Monthly, includes an article by Stephen Budiansky on something most Americans have had all too much experience with — traffic gridlock. I was particularly struck by what Budiansky has to say about what might best be called psychological gridlock,
The eeriest thing that came out of these equations, however, was the implication that traffic congestion can arise completely spontaneously under certain circumstances. No bottlenecks or other external causes are necessary. Traffic can be flowing freely along, at a density well below what the road can handle, and then suddenly gel into a slow-moving ooze. Under the right conditions a small, brief, and local fluctuation in the speed or spacing of cars — the sort of fluctuation that happens all the time just by chance on a busy highway — is all it takes to trigger a system-wide breakdown that persists for hours after the blip that triggered it is gone. In fact, the Germans’ analysis suggested, such spontaneous breakdowns in traffic flow probably occur quite frequently on highways.
A few years ago I experienced just such congestion. My wife and I were late meeting my in-laws at a zoo about 30 miles away. We headed toward the normally speedy four-lane divided highway but about 5 miles out of town came to a dead stop on the freeway.
There were “Construction Ahead” signs posted on either side of the highway so we assumed there were men and women working on the highway ahead which caused the slowdown. But when we finally emerged to where traffic resumed a normal speed, there was in fact no construction or other obstruction whatsoever (it was a Sunday afternoon). The highway was completely free.
As best we could figure out, the mere suggestion that there was construction ahead was enough to create conditions that lead to traffic completely stopped and backed up for about 1 mile and a half.