The Physics Behind Traffic Jams

In between today’s various events, I dashed into the store for milk. As I was preparing to back out of my space, I saw a little old lady pushing her cart along, not realizing that my engine was running and I was about to back out. To make a long story short, I didn’t try to dash out in front of her, or honk to hurry her along, I just waited for her to amble past. Then when I figured the universe owed me my turn to go, someone else — who hadn’t seen or didn’t care that I had just been generous — got upset at me and flicked me off when I started backing up. This other lady was furious at me becase the guy whose parking space she wanted to take was pausing so that I could back out of my space.

Maybe, if the three of us met while pushing our shopping carts through the aisles, or if we met in the park pushing toddler-bearing strollers, this woman would still have been a jerk. But probably not. Something about being in a sealed vehicle makes one competitive and irrational.

I am fortunate that I have a very easy commute, in an area where the back roads between my house and office are not only scenic and pleasant, but faster than the main highway. My commute is not terribly stressful, so I haven’t developed the habit of driving aggressively. I did, briefly, entertain the idea of saying something to this woman who was cursing me, but I just wrote this blog post instead. Not as immediately satisfying, I’ll admit, but I feel good that I didn’t sink to her level.

Anyway, here is a good essay about how a single driver’s altruistic choices — involving tiny sacrifices, like not deliberately punishing drivers who want to merge ahead of you — can erase the stop-and-go madness for a long stretch of drivers that follow.

It’s always a good idea to drive without changing speed and without competing with other drivers for bits of headway. But I’d always assumed that the reasons were philosophical rather than practical (i.e. try to be a calm, nice person.) But my above experience shows differently. A single solitary driver, if they stop “competing” and instead adopt some unusual driving habits, can actually wipe away some of the frustrating traffic patterns on a highway. That “nice” noncompetitive driver can erase traffic waves. I suspect that the opposite is also true: normal competitive behavior CREATES the traffic waves.

Suppose we push constantly ahead, change lanes to grab a bit of headway, and always eliminate our forward space in order to prevent other drivers from “cutting us off”. If tiny traffic waves appear, we will rush ahead and then brake hard, leaving larger waves behind us. Repeated action causes the waves to grow. Ironic that the angry people who drive as fast as possible might unwittingly participate in “amplifying” the very waves that they hate so much. —The Physics Behind Traffic Jams.

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