This is why I cut you off

Sometimes, the yutzim on the freeway get themselves into lockstep, and a slow lockstep at that. It’s times like these that call for action, of the sort that gets you honked and/or yelled at. But the benefits are genuine:

According to the latest physics research, rule-breakers — drivers passing you on the wrong side or changing lanes too close to the intersection — actually help smooth the flow of traffic for the rest of us. “The interesting finding is that if most of the people are law-abiding, and you have a certain amount of people who are breaking the rule, then you are actually getting the minimum chance of a [traffic] jam,” said Petter Minnhagen, a physicist at Sweden’s Umea University and an author of the paper published in the journal Physical Review E.

Weirdly enough, this started out as a study of pedestrians:

Physicists at the school uncovered this phenomenon while constructing a computer model of how a crowd of people move across a confined space, such as a pedestrian-only street. They divided the space into squares, like a chessboard, and randomly placed pedestrians in some of the squares. Like real people, the model pedestrians had a certain small probability of momentarily pausing, as if they had run into a friend or had bent down to tie a shoelace.

To make things more interesting, the researchers then tossed a few mavericks into the mix, who didn’t follow the rules the other pedestrians used. The physicists ran the simulation over and over, each time boosting the percentage of rule-breakers. At first pedestrian deadlocks worsened. But as more and more rule-breakers joined the fray, something entirely unexpected occurred: traffic flowed best when only about 60 percent of pedestrians were obeying the rules.

Simple interactions of individual cars, people, or molecules add up to large patterns in a system. The high concentration of pedestrians in a small area increases the chances of a jam, but rule-breakers made the crowds spread out.

No surprise there, really: with almost anything in motion, there’s some sort of sweet spot, and it takes a little effort to find it sometimes.

Morris Flynn, a University of Alberta professor who uses computational methods to study car traffic, agrees with the explanation. Because rule-breakers “carve out their own path,” Flynn said, they dilute large concentrations of rule-abiders moving in the same way. He pointed out an example familiar to anyone who has driven on a two-lane road: breaking the speed limit to pass a slow vehicle prevents a long chain of cars from forming.

Which I had to do Friday morning to get around a sleepy-headed Camry with its cruise control set on a stolid 58 mph. (“The letter kills, but the spirit gives life.”) In this state, incidentally, they can bust you for doing that in the left lane, much to the surprise of the Anti-Destination League.

An abstract of the study can be found here.

(Seen at Autoblog.)


  1. Donna B. »

    2 August 2009 · 5:45 pm

    It’s when the rule-breakers cause a pile-up that things get messy.

    I once drove from Shreveport to Dallas and noticed no one, absolutely NO ONE disobeying the rules (except for a little speeding here and there, which I don’t consider a horrible infraction).

    No one stayed in the left lane after passing, blinkers were blinking, nobody was tail-gating… it was a very strange experience.

    I called my daughter to see if my cell-phone would work in this apparent alternate universe.

  2. CGHill »

    2 August 2009 · 6:03 pm

    Last time I was in west Texas, which was last summer, I noticed a prodigious amount of good behavior and lane discipline, and speeds clustered around the 82-mph mark. At the time, I assumed it was due to Texans being so happy about getting a proper 80-mph speed limit that it didn’t occur to them to be disagreeable. The big rigs aren’t allowed quite that much velocity, but no one was getting in their faces either.

    Of course, the rule-breaker who overestimates his own prowess is just asking for trouble, and very often gets it.

  3. McGehee »

    2 August 2009 · 6:10 pm

    Looks as though “rules” in this case are different somewhat from “laws.” I gather that my highway strategy as recounted last year would designate me a rule-breaker because not only was I trying very hard not to drive like everybody else, I was also, to some extent, trying to discourage everybody else from driving like me.

  4. CGHill »

    2 August 2009 · 6:14 pm

    Or as either Click or Clack might say, “Don’t drive like my brother.”

  5. Donna B. »

    3 August 2009 · 12:05 am

    When I drive to AZ to visit my granddaughter, I make sure I’m in W Texas during daylight. I figure a limit of 80 means 84 minimum, recommended. I’ve noticed that cops seem to cluster where the speed limit drops, so I feel a little bit assured I can zoom zoom in the open nowhere.

    In one experiment, my husband – Mr. Law Abider – drove. He set the cruise control on whatever the posted speed limit was. He got decent gas mileage — 28 mpg in our old Caddy (but new enough to have a Northstar engine).

    The next year, I drove. I didn’t use the cruise control nearly as often and drove what I felt comfortable with, which was occasionally under the posted limit, but most of the time well over. I got 30.5 mpg.

    One place I religiously use the cruise control is when I leave Texas going into Arkansas on state highways. There’s a 15 mph speed limit drop and I can’t mentally handle it. I must have mechanical help.

  6. CGHill »

    3 August 2009 · 7:09 am

    I’ve always gotten better mileage without cruise control than with it, perhaps because I’m not making constant corrections, which most cruise controls seem to be doing. I ran about 27-28 mpg in west Texas.

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