Evacuation performance of pedestrian flow under limited visibility in straight corridor

In the event of power outages or fires, visibility in buildings can be severely reduced, posing serious challenges to safe evacuation. However, the impact of limited visibility on pedestrian flow dynamics remains poorly understood. To address this gap, this study conducted a series of controlled pedestrian flow experiments in a straight corridor, examining the impact of both normal and limited visibility across different crowd densities. Results show that lane formation as a typical self-organizing phenomenon occurred under both visibility conditions. The difference in pedestrian speed between the two visibility levels exhibits a piecewise linear relationship with density: in the relatively free stage (ρ < 2 ped/m2), speed differences decline with increasing density, while in the constrained stage (ρ ≥ 2 ped/m2), the difference stabilizes at a lower level. In addition, under limited visibility, pedestrian flow rate maintains linearly related to exit width but is consistently lower than that under normal visibility. The flow also becomes less continuous, with a higher likelihood of congestion near the exit. From a spatial perspective, limited visibility leads to higher local densities, as evidenced by smaller occupied areas and shorter distances to nearest neighbors, indicating the formation of a more compact crowd structure. These findings enhance our understanding of pedestrian flow under limited visibility and offer valuable insights for the development of evacuation strategies and crowd management. In practical applications, crowd control strategies under limited visibility should be adapted according to the dominant factors at different density levels.