Thursday, 6 March 2008

Traffic Jams

While I'm feeling scientific, I'd love to compare this - below - with a video of a dance floor. I don't see why you couldn't do exactly the same experiment.

Would the traffic jams - if any - follow a similar mathematical rule? Specifically, would they propagate backwards at two-thirds of the average speed the dancers go at when there's no traffic?


Johanna said...

awesome vid! Those "lags" are caused by people not paying attention and/or not keeping up with the changes in speed and/or CELL PHONES.

Shut up and drive/dance!!!

David said...

Interesting video and explains all those "what was that hold up all about?" type of questions we get when driving on the motorways.

There is one minor difference though and that is that the cars are all trying to make progress in a single direction. In tango some dancers like to travel and make progress (like me), whilst others just like to stay where they are and only move on when they eventually notice an intimidating wall of dancers built up behind them in the line of dance (even then they don't always take the hint...).

I have often wondered what is the major factor to getting a nice flow of motion at a milonga. Is it the leaders, the combination of partners, the selection of music?

I've never been able to predict at the start of a milonga whether it's going to be a lovely flowing milonga where I can concentrate on the music and my partner, or a navigational hell!

msHedgehog said...

@johanna - I think the point is that it still happens, and cannot be prevented, even if all your drivers are doing their best to move at a constant speed around a completely regular circle, and mobiles and so forth are removed.

@David - I think it would still happen to some degree (and for the same reasons) if you removed that difference and duplicated the experiment exactly, with a circular single-lane track, and a team of competent and cooperative dancers actively trying to progress at the same constant speed. Whether the jams happen, and when, probably doesn't depend on the things it's normally assumed to depend on. What interests me first, though, is whether the relationship between the speed of the jam and the speed aimed at would be the same as it is for cars.

david said...

In one of my regular classes 2 or 3 years ago, the teacher was trying to teach us some floorcraft. He partitioned off the dance floor with some chairs and told us to dance in the line of dance, no overtaking, and if there was space in the line of dance ahead of us, to move into it. He then proceeded to move the chairs to make the dance floor smaller and smaller to simulate dancing in a crowded milonga.

I remember that as the dance floor grew smaller, the smooth progress of the dance changed at a point to alternating periods of being able to travel for a while then having to remain static until a space opened up in front of me. which would be the same as these compression waves you see on the video.

I didn't really notice though how the compression wave moved at the time! If I ever do a similar workshop again, I'll take notice...

I would guess that for the cars, it is the lag between the drivers vision and action of their feet on the pedals that causes the compression wave effect. If that lag is similar for dancers, then it seems reasonable that it should follow similar rules.