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.

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2 Responses to The Mystery of Traffic Snarls

  1. Esteban says:

    I remember watching a documentary years ago on TV, where they mentioned the same “wave pattern” moving against the traffic. If people would just stick to their lines it would go more smoothly. A horroble plus on Argentina, a lot of drivers, upon stuck traffic, get off the road into the dirt, trying to get ahead of it. A hateful and selfish attitude.

    Seems both you and Mark are having “line issues”

  2. markitude says:

    First, the absurd: Replace stop lights with full dragstrip style countdown sequence – Yellow, yellow, yellow…GREEN!. Of, course you’d have to arrange people by reaction times and their car’s capabilities or you’d have one huge catastrophe when the light changed.

    Ok – reality – great observation on the wave. And, add brake tapping to watch the wave compress. Your point on the instinctive competitiveness that occurs during low speed pass attempts is on target. Another factor I find is your satisfaction with a given speed depending on whether there is open road ahead. If open road, I’m content driving around the speed limit on most occasions. But, if there are cars ahead, I feel trapped, anxious, and desire to pass.

    It’s been said “Patience is the trait we admire in the driver behind us, but not in front of us…”

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