Why We Should Love Traffic Jams

Posted on October 23, 2010


Okay, I don’t love traffic jams. In fact, I hate them. They make me late, they make me tense, and they make me smack the steering wheel and hurt my hand. But traffic jams are an example of a phenomenon that is everywhere in our lives. And without it, we wouldn’t exist.

It’s the tendency for things to clump together.

In the perfect driving world we all imagine, the cars and trucks are spread out evenly, all moving at the same speed. They don’t slow down or get too close to each other. Every trip is smooth and quick. No accidents, flat tires, tailgaters, or slow pokes.

As we both know, however, life doesn’t work that way. Even with no discernible reason, traffic builds. Vehicles bunch together. Drivers slow down and speed up. Sometimes they come to a complete stop, and after creeping along for minutes, they remember how to drive again and the traffic jam dissipates. Then, by the time we reach the imagined problem, there’s nothing there. And we’re on our way, a little confused but happy just the same.

What is this clumping thing all about? Sometimes it’s the result of conscious decisions. For example, people like to be near other people. If you look at any map showing population distribution, you’ll see that that are always places that have a lot of people in a small area (cities and towns). In between, there are large spaces that are empty, or at least much less densely populated. We measure this density with a number, saying New Jersey has about eleven hundred people per square mile. But this is an average, found by dividing the entire state’s population by its land area. There are places in New Jersey where there are more than eleven hundred people living within a given square mile, and there are other places where the number would be very low, even zero. But you’ll never find people evenly spaced. There are always clumps.

Flip a coin a thousand times and you’ll get about 500 heads and 500 tails. Not exactly, but pretty close. If you write down the results as a sequence, though, you won’t find a predictable pattern such as head-tail-head-tail-head-tail. Much more likely, you’ll see heads or tails appearing in strings of different lengths, as small sub-patterns within the randomness. That’s how most things work. Make a batch of chocolate chip cookies and you’ll notice that every cookie has some chips; they never end up all in one cookie and there’s almost never a cookie with no chips. But one cookie may have seven or eight chips, while another may have just three.

As humans, we like to explain why things happen. When we forget this clumping tendency we can misinterpret things like statistics. Stores, especially large chains, study sales figures, comparing this week’s numbers with those of last week, or today’s sales with those of the same date in past years. And then they try to figure out why the dollars went up or down. But built into every one of those collections of digits is clumpiness. Anyone who’s ever worked in a retail store knows this: the place gets busy for a while, and then it slows down. Sometimes it’s because a lot of people just got out of work, or there’s a storm coming, or tomorrow is Thanksgiving. But more often there’s no reason that anyone can identify. It’s just the way it is.

Similar spikes in crime, disease, and natural disasters may seem alarming, and the media are skilled at taking advantage of our misinformed reactions to those events. Any increase in a city’s murder rate is presented as a crime wave. Above-average incidence of the flu quickly becomes a perceived epidemic. An extra hurricane or two and we’re filled with anxiety about runaway climate change. We keep looking for outside causes, when the real explanation may be simple mathematics.

I said in the first paragraph that without clumpiness, we wouldn’t exist. That’s because if you took all of the atoms in the universe and spread them out evenly, there would be just atoms. There would be no galaxies, stars, or planets. Or life. But if you look up at the night sky, you see densely packed collections of matter: stars and planets held together by gravity and separated by vast regions of empty space. That clumpiness is a beautiful thing, and we owe our existence to it. I’m going to try to remember that the next time I’m bouncing my fist on the steering wheel and straining my neck to see what’s going on up ahead. It could be a flat tire, or an accident, or more road construction.

Just as likely, it’s cars doing what they do naturally: forming those wonderful clumps.


Posted in: In Over My Head