Agent-based simulation of hindering effect of small group behavior on elevated interval evacuation time along urban rail transit

Passenger evacuation on elevated rail lines has always been a challenge for rail transit safety operation and evacuation planning. Though the importance of passenger behavior to evacuation has been recognized gradually, limited research focused on the influence of small group behavior on evacuation of elevated rail transit system. This paper conducted a questionnaire survey about passenger willingness of small group behavior in elevated interval evacuation firstly. Then, an elevated interval evacuation with different small group proportions, small group gathering status and the design of interval evacuation platform was simulated using multi-agent-based model, and the influences of small group behavior on evacuation were analyzed quantitatively. Three types of evacuation time, namely t(-train),t(-risk), and t(-total) for passengers alighting from trains, leaving from risk area and exiting from the stations respectively, was calculated and compared in with and without small group conditions. Results indicated that the small group behavior show a stronger hindering effect on the long and narrow evacuation walkway platform which induced dramatical increase for total evacuation time. When the interpersonal maximum distance equaled 1 m, t(-total) could be increased by 64.9% in unidirectional evacuation and by 52.0% in bidirectional evacuation compared to where interpersonal maximum distance equaled 2 m. Besides, relatively narrow evacuation walkway may deteriorate unidirectional evacuation condition sharply than bidirectional evacuation. Considering the significantly hindering effect of small groups on elevated interval evacuation, it was suggested that small group behavior should be taken into consideration seriously in evacuation plan and evacuation facility design in the future.