Turning dynamics of pedestrian social groups on a stair landing: A field study

Pedestrian social groups play a critical role in crowd dynamics. However, how group members interact during turning on stair landings remains unclear. In this study, a field observation was conducted on a stair landing to investigate the turning dynamics of social groups. A total of 122 descending social groups and 40 individuals were observed, and their trajectories were extracted. The results highlight that the position of group members contributes significantly to the movement characteristics. Specifically, within the same group, outer members (with larger turning radii) have higher walking speed but lower angular speed, whereas inner members exhibit the opposite pattern. As the outermost member tends to arrive at the landing earlier and adjust movement direction sooner than others, a left-right asymmetry in the relative positions is observed within social groups. During turning, group members dynamically regulate their movement by reducing speed and shortening interpersonal distances, enabling them to re-establish a spatiotemporally cohesive structure. Moreover, a stepping strategy for maintaining group cohesion is found, whereby social groups exhibit shorter step lengths and step durations compared to non-group pedestrians when the speed exceeds 0.8 m/s. Finally, the relation between movement time and walking radius is established to estimate the travel paths of social groups on stair landings. These findings have implications for group walking modeling and the design of public spaces.