Traffic and How To Help

Jason Modisette submits for your consideration a plan by which to ease traffic congestion.

I've started keeping a big gap in front of me when I drive (say 2-3 car lengths when traffic is stopped, 5+ when it's moving >= 20 mph). I try to keep the space large enough that a pretty timid and incompetent driver can confidently change into it. I do this because I suspect that a small fraction of drivers doing it would eliminate most traffic jams and even one driver doing it can significantly improve the traffic situation around him.

What causes a traffic jam? I suspect that it's botched lane changes. When a car attempts to change lanes but doesn't have enough room to change into (for instance because the destination lane slowed down dramatically during the change, or even was already stopped), he can end up blocking his original lane until the destination lane starts moving again. This is the most obvious mechanism I can think of for an increased density of cars to result in dramatic average speed reduction.

If a small fraction of the drivers keep gaps in front of them, many of the people who want to change lanes will take advantage of the gaps to do it. This makes a botched lane change less likely. (I've still seen it happen, when for some reason the lane-changer changed lanes right at the front of the gap, but it's rare). If the lanes have a significant differential speed, then one such gap-driver can draw off a good fraction of the people who want to change lanes as the two lanes slide past each other.

In some specific circumstances a single driver doing this can totally eliminate a traffic jam (for a while). I've seen this happen when the traffic jam was caused by two lanes merging into one, with no other cause of traffic downstream of the merge. By driving in the kept lane and ruthlessly letting every single person in the other lane go in front of me, once I hit the merge point traffic behind me had sped up to normal speeds - the jam was gone. Eventually it's bound to recur, but maybe not as soon as you'd think, because some of the people who are planning to run up to the front of the jam and force their way in (a common way to cause botched lane changes) can instead merge easily in front of me (when I'm approaching the merge point).

My own sense, aside from righteous furious anger at people who plan to run up to the front of the jam and force their way in, is that, indeed, Jason's plan is effective. If drivers cooperated more in times of congestion, the congestion would be eased. Of course, polite driving can't fully compensate for the effects of increasing vehicle density, which is the primary cause of slowdowns.

I look forward someday to reading a good popularization of the science of traffic congestion.

Posted by Greg at July 1, 2003 4:55 PM