Intragroup dynamics and splitting characteristics of social group movement through a funnel-shaped bottleneck

Social groups are common in crowd gatherings and events. In this study we explore the trajectories and interactions of groups consisting of more than 4 pedestrians. Although previous studies indicate that such groups have a tendency to split in free space, precise empirical data for bottleneck movement is still limited. Here we fill this gap by performing exploring experiments on the dynamics of groups of 5, 6 and 7 persons through funnel-shaped bottlenecks of two different widths. The intragroup dynamics and the splitting characteristics of groups are analyzed on macroscopic, mesoscopic and microscopic scales. The macroscopic scale results reveal that increasing bottleneck width improves group speed and reduces severe deformations. The bottleneck width significantly affects group shape, while group size significantly affects group speed in narrow bottlenecks. The mesoscopic scale results confirm the existence of mesoscopic components by identifying the heterogeneous bonds between each pair of adjacent sequence members, i.e. stable and unstable bonds. The sub-individual is only connected by unstable bonds and subgroup is formed of stable bonds. The reduction in bottleneck width negatively affects the average speed of subgroups but has little impact on their spatial requirements and members’ relative positions. So the stable spatial characteristics of subgroups are measured as the spatial threshold for the splitting of unstable bonds. The microscopic scale results investigate the split state of unstable bonds within the group. The spatial distributions of split states differ evidently between 5-person and 6, 7 persons groups. The split behavioral strategies of groups are more sensitive to intragroup spatial restriction for narrow bottleneck (0.8 m), but more sensitive to environmental restriction for wide bottleneck (1.5 m). The intragroup disturbance caused by splitting is assessed exploringly based on the concept of ‘energy conversion-spillover’. The results can help improve crowd management, better design of bottlenecks, and more realistic description of group dynamics in modeling approaches.