Empirical analysis of the lane formation process in bidirectional pedestrian flow.

This paper presents an experimental study on pedestrian bidirectional streams and the mechanisms leading to spontaneous lane formation by examining the flow formed by two groups of people walking toward each other in a mock corridor. Flow ratio is changed by changing each group size while maintaining comparable total flow and density. By tracking the trajectories of each pedestrian and analyzing the data obtained, five different phases were recognized as contributing to the transition from unidirectional to bidirectional flow including the spontaneous creation and dissolution of lanes. It has been shown that a statistical treatment is required to understand the fundamental characteristics of pedestrian dynamics and some two-dimensional quantities such as order parameter and rotation range were introduced to allow a more complete analysis. All the quantities observed showed a clear relationship with flow ratio and helped distinguishing between the different characteristic phases of the experiment. Results show that balanced bidirectional flow becomes the most stable configuration after lanes are formed, but the lane creation process requires pedestrians to laterally move to a largest extent compared to low flow-ratio configurations. This finding allows us to understand the reasons why balanced bidirectional flow is efficient at low densities, but quickly leads to deadlock formation at high densities.