Traffic Jams

I have been thinking over the past several years about traffic jams and what causes them. The idea is that they do not happen instantaneously (you never find yourself at the front of one, do you?), but rather grow from rather unremarkable circumstances. My father, my wife, and I have discussed this and come to the fuzzy conclusion that one could make a mathematical model of a traffic jam if one were so inclined. We are not. But we theorized that snarls are caused not by actual incidents (ie, accidents/roadblocks/sinkholes, whatever) but rather by a geometric progression moving backwards from a point of an event in time. That is, one need make only a slight variation from a flowing traffic pattern to begin the chain of small, but multiplying and growing greater, incidents in the waves of traffic behind you. It's like the butterfly effect, but plausible.

For example, in smoothly-flowing traffic, you may overcorrect when changing lanes. This may cause the driver in the next lane to brake suddenly. The person behind him brakes as well, losing 10-15 mph in speed over one to two seconds. You, who have swerved into a new lane, are traveling slower than upcoming traffic as well. While all the cars in your immediate area are able to rapidly recover speed and move on (the road is clear in front of you--you just slowed down, thereby letting preceding traffic create a gap between you), the wave of braking will move backwards from that point and grow more severe--particularly if someone behind you isn't paying attention and has to brake even more sharply. Perhaps not immediately, but even an hour later, you have gridlock, a situation where conditions have multiplied to the point that the loss of speed and number of cars on the road adds up to conditions that cross some threshold point and movement is impossible until you get to the front of the line.

This website, which I just found, has more. He's got better graphics, too. Enjoy.

Now I wish someone would address the duration of traffic jams and the point at which they are at their peak and begin to decline. Be sure to read page 2 of the above site for an interesting recommendation for helping curtail the length of time it takes a traffic jam to run its course.