Empirical study on spatial characteristics of dyads in a unidirectional corridor

Groups are an important component of pedestrian crowds in public areas, with dyads being the most common formation. Compared to individual pedestrians, dyads often exhibit distinct behavioral characteristics. For example, different relative positions among group members result in distinct spatial characteristics. Understanding these is essential for effective design of pedestrian facilities and safety evacuation. Existing researches about dyads mainly take subways or trade centers as scenarios, and pay insufficient attention on the change rule of dyads’ spatial configuration at different densities. To address these shortcomings, this study examines the movement behavior of pedestrian dyads under varying density conditions using surveillance footage from the entrance passage of a scenic area in Beijing. A total of 432 pedestrians, including 69 dyads, were tracked using PeTrack. Dyads were identified through movement patterns, interpersonal interactions, and clothing features. A computational method was developed to quantify spatial configurations and analyze how these patterns vary with crowd density. Results show that dyads predominantly prefer walking side-by-side. On average, in-group distances in side-by-side patterns are smaller than those in vertical-like patterns. Density significantly affects in-group distances of dyads. At densities below 0.8 m⁻², dyads adapt to the environment by reducing in-group distances as density increases. When density exceeds 0.8 m⁻², dyads tend to abandon side-by-side patterns and adopt stair-like or vertical-like patterns to navigate limited space or overtake other pedestrians. Overall, the spatial characteristics of dyads are influenced not only by the physical and psychological attributes of group members but also by environmental constraints. Dyads maintain internal cohesion and avoid collisions by dynamically adjusting their interpersonal distances and relative positions. Additionally, a computational method for quantifying group spatial characteristics is proposed, providing methodological guidance for quantitative pedestrian behavior research. These findings contribute to evaluating the safety capacity of public spaces and the service level of pedestrian facilities.