Simulation of spontaneous leader–follower behaviour in crowd evacuation

Abstract

The leader–follower (L-F) relationship is believed to be the fundamental mechanism explaining the collective behaviour of a crowd. However, previous models are inherently limited in that they simulate a pre-defined L-F behaviour using simple heuristics. In this paper, we propose a new approach to measure the emergence of spontaneous L-F behaviour in an evacuating crowd using an information-theoretic and model-free method, i.e., transfer entropy (TE). The dynamic characteristics of evacuees (e.g., their trajectories, movement patterns and density plot) in a room (or corridor) are clearly visualised by the proposed TE-incorporating force-based model. The results show that the overall evacuation time decreases as the TE threshold increases. The trajectories occur in congested clusters when the TE threshold is low, but become more dispersed and uniformly distributed in scenarios with higher TE thresholds. In terms of group size, a spontaneous L-F group normally consists of one leader and one follower. L-F groups of larger-size (i.e., more than three followers of a leader) tend to disappear with increasing TE threshold. Lastly, we examine the location of spontaneous leadership emergence. Irrespective of the geometric layout or the number of evacuees in a room or corridor, the threshold at which distinct L-F patterns emerge is always approximately I¯TE = 0.5. By innovatively integrating the TE approach into a force-based model, this study suggests a novel method for leadership identification during crowd evacuation given no prior knowledge.