# conorjh

## Movement of crowds and of urban traffic.

Anders Johansson (University of Bristol) Multi-scale human mobility (BCCS seminar Tuesday, 24/4/2012).

A talk about how people move, with sections about people walking in crowds and crowd safety, for example, at the Hajj and about traffic and road usage. It was an overview talk so hard to summarize, one of the most interesting pieces was a video of a large crowd at the Hajj walking to Ramy al-Jamarat for the stoning of the Devil. In the video the density had been color coded, so that back-ward moving stop-go waves were clearly visible. This is apparently the source of danger, you should avoid large unsegregated crowds where complicated internal crowd dynamics occurs, so several narrower passages would be safer. The speaker and his team do crowd modelling by taking video and removing individual and replacing them with a modeled individual but leaving the other members of the group as before, the error is the displacement of the modeled individual from the position of the individual they replace, this is then optimized by changing the rules governing the movement of the model. The model is basically a speed adjustment coming from a function of the displacement of nearby individuals, it depends on $r$ and $\theta$ but they assume the function is separable into a $r$ function and a $\theta$ function. It is hard not to worry that the error function is poor since it doesn’t take into account the adjustments the other individuals would’ve made in response to the movement of the modeled individual, but I suppose that doesn’t matter for small values. Anyway, there model accounts for lane-formation in crowds moving in two directions along a corridor. This is some interesting function of densities, with some sort of lane formation transition, there was a question about this, but it wasn’t really discussed. There was also mention of a crowd movement experiment, people were told they had to keep moving and keep within a meter of at least one other person, five people were secretly told to move in a specific way, this was enough to entrain a crowd of 100. Conversely, in fire alarm test, if the alarm is a simple bell people often pause and wait from someone else to move first and determine the route, if the alarm gives simple spoke instruction evacuation happens much quicker. There was also lots about traffic, with courier data for London, but not many details given.