The Mystery of Traffic Snarls

You are traveling along the interstate and the traffic slows down.  People change lanes in a desperate attempt to find a faster path.  The traffic speed comes down to a crawl.  More desperate lane changing.  The clot reaches its maximum and then without reason the road clears up and, a couple at a time, cars break free and return to normal cruise speeds.  What happened?

A few years ago I came across this site on traffic waves.  A self described science hobbyist had studied the phenomenon and has published his observations and conclusions.

You might even think that this cannot happen without a large volume of traffic.  Have you ever experienced the wave effect of a line of cars leaving a traffic light?  It can be four cars or fifteen.  Assuming that they are all waiting for the light to change and therefore paying attention why don’t they all accelerate when the light goes to green?

Instead you see the first car in line go about ten to 15 feet before the next car accelerates from a stop and so on.  Viewed from the side it forms a wave pattern as the movement moves from the front of the line to the back.

Sometimes it takes only one other car on the highway to cause a clot.  Have you ever been traveling along, maybe about ten miles per hour over the posted speed limit and slowly come up on another car in your lane.  As you signal and move to the passing lane the car now to your right increases its speed.  Is this due to a reaction from the primitive portion of this driver’s brain? Is some ancient synapse telling his foot to increase its pressure so that he will not be put in a position of vulnerability?

You can see-saw back and forth a few times before you tromp the accelerator and put distance and evil thoughts between you and the irritating driver.  While you were in limbo you were emulating that wave pattern.

I used to travel from one  end of Connecticut to the other and would travel at pretty much a consistent speed and invariably come across moving clots of cars.  All lanes would be taken up with vehicles that were within a few miles per hour of each other and yet they would not stay in a nice line in the right lane.  They had to spread out to the available lanes.  Even geese know enough to use the V formation so that only one goose at a time has to work hard.