Crowd dynamics determined by more than physical constraints

A long time ago, while still doing a bachelor degree in biology, animal cognition was a pet project of mine. Ants and bees or ethology methods were highly intriguing and paved my way towards more technology-oriented studies of behavior. I still keep an eye on this field and the following paper from one of the lab I followed recently caught my attention (via): Moussaïd M, Perozo N, Garnier S, Helbing D, Theraulaz G (2010) The Walking Behaviour of Pedestrian Social Groups and Its Impact on Crowd Dynamics. PLoS ONE 5(4).

(Pedestrian flows in Toulouse, France as observed in this study)

Some excerpts I've found interesting (my emphasis):

"Human crowd motion is mainly driven by self-organized processes based on local interactions among pedestrians. While most studies of crowd behaviour consider only interactions among isolated individuals, it turns out that up to 70% of people in a crowd are actually moving in groups, such as friends, couples, or families walking together. These groups constitute medium-scale aggregated structures and their impact on crowd dynamics is still largely unknown. In this work, we analyze the motion of approximately 1500 pedestrian groups under natural condition, and show that social interactions among group members generate typical group walking patterns that influence crowd dynamics. At low density, group members tend to walk side by side, forming a line perpendicular to the walking direction. (...) when crowd density increases, the group organization results from a trade-off between walking faster and facilitating social exchange."

Why do I blog this? what is interesting in this work is that the crowd dynamic model should take into account the presence of people who put more emphasis on social activities than on movement efficiency. It basically shows that pedestrian flows are complex and not determined by physical constraints induced by other pedestrians and the environment, but also significantly by on less utilitarian reasons (communicative, social interactions among individuals). This result is perhaps taken for granted in the social sciences but it's curious to observe it with this kind of modelling work.