
Traffic Ghost Hunting (2013) - dnetesn
http://nautil.us/issue/16/nothingness/traffic-ghost-hunting-2
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perl4ever
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".

~~~
ubernostrum
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.

~~~
perl4ever
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.

~~~
ubernostrum
_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?

~~~
perl4ever
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.

------
kwhitefoot
William J. Beaty did a better write up on this subject many years ago:
[http://trafficwaves.org/](http://trafficwaves.org/)

