A model for describing the hydrodynamics of crowds

By studying the movement of runners at the start of marathons, researchers from the Laboratoire de physique (CNRS/ENS de Lyon/UCBL) have just shown that the collective movements of these crowds can be described as liquid flows. Their results, published in Science on January 4, 2019, have enabled them to predict how fluctuations in speed and density are transmitted through massive crowds. The flows observed before a 2016 race in Chicago subsequently helped predict those of thousands of runners in the starting corral of the 2017 Paris marathon. Precise simulations of the movement and behavior of crowds can be vital to the production of digital sequences or the creation of large structures for crowd management. However, the ability to quantitatively predict the collective dynamic of a group responding to external stimulations remains a largely open issue, based primarily on models in which each individual's actions are simulated according to empirical behavioral rules. Until present, there was no experimentally tested physical model that describes the hydrodynamics of a crowd without assuming behavioral rules. Researchers from the Laboratoire de physique have provided a first equation of this type, deduced from a measurement campaign conducted on crowds numbering tens of thousands of individuals.