Traffic waves, cars peak

Have you ever had that experience of waiting through a traffic jam only to find that there was no accident, no construction, no constriction, no cop by the side of the road. Just a giant vehicular bolus that came and then went. I used to think that the jam-causing blockage had been cleared up by the time I got to the front, but it turns out the real answer is more insidious. When traffic is dense enough, standing waves of car-particles can build up quickly and with very little initial disturbance. In the extreme, one injudicious tap on the breaks can ruin everyone’s commute. Don’t believe me? Here’s a little interactive graphic to show how it works.

What Are Traffic Waves and Why Do They Happen So Much?

Scroll down to the circular highway diagram and press the “Hit the Brakes” button.


Still skeptical? Here is an experiment with real cars that demonstrates the same idea.

But there’s good news too. Traffic waves are an emergent property of a dense particle flow. But that flow is becoming less dense. Believe it or not, there are fewer and fewer cars on American roads every year. Listen to this trifecta.

1. We own fewer cars.
2. The cars that we own are being driven less.
3. The driving that we’re doing is more fuel efficient.

This is not to pretend that cars will be gone anytime soon, but those trends are all moving in the right direction, if you believe this (PDF) report from Michael Sivak at the Univeristy of Michigan: Has Motorization in the U.S. Peaked?. Or you can just read the summary on Greentech Media: More Evidence That America May Have Reached ‘Peak Car’. Nobody knows for sure if these changes are permanent or if we’re still experiencing a post-recession hangover. But it warms the heart in a world of bad news. Then again, I don’t sell cars for a living.

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