Analysis of movement behavior of pedestrian social groups through a bottleneck

Pedestrian social groups are an essential part of a crowd. In emergency situations, they may become principal victims during evacuation from buildings, such as bottlenecks in corridors. However, empirical data on the dynamics of social groups through bottlenecks are limited. In this paper, a controlled experiment was performed to study movement features of social groups through a bottleneck with different widths (i.e., 0.8, 1.4 and 2.4 m). There were 60 participants in the experiment, forming four crowd compositions (i.e., 60 groups of singles, 30 groups of dyads, 20 groups of triads and 15 groups of four-person groups). After extracting their movement trajectories in the video recordings, offset angles, passing performance, interpersonal distances and angles in group walking, relative positions in social groups, etc. were analyzed. The results highlight that the negative effect of bottleneck width on instantaneous speed for larger groups is more significant than for smaller groups. The cooperative behavior of large groups is beneficial to the instantaneous speed of pedestrians under wide bottlenecks. The size of the groups has no evident influence on lane formation. Singles adjust their movement directions more flexibly, and the offset angles of large groups are smaller. Good passing performance can be reflected in large groups through wide bottlenecks. It is proved that interpersonal distances and angles between group members depend on the group size, bottleneck width and pedestrian flow state (free and congested flow). Under the limitation of narrow bottlenecks, the walking structures of large groups can lead to diverse walking structures. The phenomenon of recurring splitting and rejoining of pedestrian social groups can be observed. These findings are helpful for crowd management in buildings.