[zck]

Some Japanese scientists did a study to show how traffic jams can appear of of nowhere. They told 22 drivers to drive in a circular path at 30 km/h. A traffic jam appeared, and moved backward. The video is here: http://www.youtube.com/watch?v=Suugn-p5C1M

[cema]

Jams move backward, a well known phenomenon. That they appear "out of nowhere" is more interesting.

[steamer25]

It is interesting but not inexplicable. For instance take a scenario where one driver sloooowly passes another on a two lane road. This effectively clotheslines the road and causes anyone who would drive faster yet to pile up behind the two cars--maybe even apply their brakes.

Again, consider a sudden lane change that cuts off someone who's already in the lane being entered.

Yet again, consider that most on-ramps are essentially a reduction of available lanes.

Any time one car slows down for any reason, inertia kicks in--they do not immediately return to speed.

In this case, small variations in speed mean that some drivers eventually catch up to others. Then they slow down a bit which reduces the space behind them. The problem is that the road is nearing peak capacity and has little tolerance for deviations.

[kyro]

It's not 'out of nowhere.' It's because we're humans. We're paranoid and reactionary. You wouldn't see that with robots.

[req2]

If I say I made a cake 'from scratch' (idiom: 'from nothing'), do you quibble that flour and eggs were indeed used, and that they are clearly not 'nothing'?

[kyro]

Mentioning how you made a cake from scratch and linking to a video of seemingly scientific research claiming an event to happen out of nowhere and for no apparent reason are two completely different things, due to the two completely different contexts.

[tlrobinson]

I think his point was that we all understand that "out of nowhere" doesn't mean "magically", at some level it has to be the drivers' fault.

The video doesn't even say "out of nowhere", it says "for no apparent reason".

[randomwalker]

Cynical much? How about it's because we have bounded cognitive abilities, limited perceptive accuracy and slow reaction times?

[dkarl]

You're forgetting the natural caution and fearfulness that protect us from depending too much on our limited abilities when safety is at stake.

[apotheon]

That too.

[kragen]

You can certainly program robots to do that. The question is whether you can program them not to without losing something important (robustness against unexpected conditions or malicious robots, for example).

[RyanMcGreal]

Emergent network phenomenon is emergent.