Gait synchronisation in pedestrian dyads: The influence of social interaction

Spontaneous gait synchronisation is commonly observed in pedestrian groups and has been studied extensively in controlled settings. Here, we investigate this phenomenon in a natural environment using a pedestrian trajectory dataset collected with range sensors in a public space, along with annotations for social groups and their interaction levels. To quantify synchronisation, we analyze the lateral periodic swaying of pedestrians, computed as orthogonal displacements from smoothed trajectories. Using the Hilbert transform, we derive instantaneous phase of pedestrians' gait residuals and then compute relative phases for all dyads. Additionally, we calculate the Gait Synchronisation Index (GSI) to quantify the level of synchronisation between pedestrians. Results show significantly higher GSI, stronger phase locking around zero, and lower phase variance in dyads with high interaction levels compared to less interactive pairs and randomly chosen pairs of pedestrians. These findings highlight the role of social interaction in gait synchronisation and provide insights into crowd dynamics and motor coordination, with potential applications in socially-aware robotics and intelligent transportation systems.