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Traffic Ghost Hunting (2013) (nautil.us)
8 points by dnetesn 2 days ago | hide | past | web | favorite | 7 comments

If there are in fact traffic jams caused by "nothing at all", I would assume there is a critical density - in other words, everyone is following too closely. Did the article point that out and I missed it?

...after looking again, yes, it did, but it seemed to avoid saying explicitly "nearly everybody tailgates and it messes things up, duh".

Waves of slow traffic don't require tailgating, and easily form either way. The biggest root cause is variance in driver reactions: someone ahead of you slows down, you notice their brake lights, you step on your brake pedal. But how quickly do you notice and react? And how quickly does the person behind you notice and react to your braking?

The people on the slower end of the reaction time spectrum will have to brake longer and harder, causing the people behind them to have to brake longer and harder, and the people on the slower end of reaction times behind them will brake harder still... and eventually you get the effect amplified to the point that traffic is coming almost to a dead stop despite no obstacle in the road (other than traffic itself) causing it.

All of this can and does happen independently of whether people are tailgating. Autonomous vehicles can, in theory, maintain very small following distances behind each other and avoid this problem because they react so much more quickly and (in some visions of the future) can communicate wirelessly with each other to coordinate a reaction. Humans can't do that.

If I left enough space in front of me, then I can adjust my speed without braking. If I left enough space in front of me, then reaction time isn't a limiting factor.

I think you just can't imagine leaving that much space. Which is not surprising, because if people in general could, then we wouldn't have the traffic jams.

It seems to me that tailgating by definition is following too closely to be able to react in time to what's ahead. You seem to feel it can be something else.

It seems to me that tailgating by definition is following too closely to be able to react in time to what's ahead.

By your definition, the people with slower reactions who amplify traffic waves aren't tailgating. By your definition, if they were tailgating, they would've rear-ended the vehicle in front of them.

Perhaps you'd like to try again?

In the spirit of cooperation which is necessary for any discussion, I was adhering to the implied definition of "react" in your previous post, as I understood it.

I don't think you're being consistent with yourself now, in saying "react in time" means "to not rear-end", nor are you rightly attributing that to my definition of tailgating.

You're entitled to your opinion about a definition, but it's not worth getting overly offended about. Sometimes generalizing a definition changes what falls under it, but it becomes in a subtle way better. I think this is sort of an "is Pluto a planet" issue, only I'm on the other side than in that case.

Shockwave traffic jams recreated: https://m.youtube.com/watch?v=Suugn-p5C1M

William J. Beaty did a better write up on this subject many years ago: http://trafficwaves.org/

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