Mechanical response of dense pedestrian crowds to the crossing of intruders

TL;DR

This study investigates how dense pedestrian crowds respond to intruders, revealing both mechanical-like features and anticipatory behaviors that challenge simple force-based models of crowd dynamics.

Contribution

It provides experimental evidence that dense pedestrian interactions differ from granular media, highlighting the importance of anticipation and lateral displacements in crowd response.

Findings

Presence of a depleted region behind the intruder

Crowd responses include anticipatory lateral movements

Mechanical models alone are insufficient to describe dense crowd behavior

Abstract

The increasing number of mass events involving large crowds calls for a better understanding of the dynamics of dense crowds. Inquiring into the possibility of a mechanical description of these dynamics, we experimentally study the crossing of dense static crowds by a cylindrical intruder, a mechanical test which is classical for granular matter. The analysis of our experiments reveals robust features in the crowds' response, comprising both similarities and discrepancies with the response of granular media. Common features include the presence of a depleted region behind the intruder and the short-range character of the perturbation. On the other hand, unlike grains, pedestrians anticipate the intruder's passage by moving much before contact and their displacements are mostly lateral, hence not aligned with the forces exerted by the intruder. Similar conclusions are reached when the intruder is not a cylinder, but a single crossing pedestrian. Thus, our work shows that pedestrian interactions even at high densities (3 to 6 ped/m 2) do not reduce to mechanical ones. More generally, the avoidance strategies evidenced by our findings question the incautious use of force models for dense crowds.