Effect of height constraints on unidirectional pedestrian flow

Abstract

In case of fire evacuation, pedestrians would have to utmost minimize their exposure to smoke and meanwhile escape as fast as possible. Under these circumstances, the smoke layer forms a height constraint for the pedestrians. Understanding pedestrian movement features, especially in response to the discrepancy smoke layer heights, is vital to the evacuation safety evaluation. In the present paper, a series of unidirectional pedestrian movement experiments under controlled laboratory conditions were performed by setting five different height constraints (H = 1.0, 1.2, 1.4, 1.6 and 2.0 m). The trajectories of each pedestrian in all scenarios have been extracted from video recordings of the experiments. With these data, typical pedestrian behaviors including lane formation and overtaking have been identified and discussed. Time-space characteristics were also detailed to explore the effect of height constraint. As indicated by the distribution of the nth-nearest neighbor, the available heights only have a slight influence on the collision avoidance feature. However, the height constraints do affect the speed and specific flow with increasing pedestrian density. For a height constraint of H = 1.2 m, the pedestrian speed presented a clear drop when compared with the height constraint of H = 1.4 m. What is more, in the density range of this study, the maximum flow is not observed for height constraints of H = 1.4, 1.6 and 2.0 m, however, the flow reaches its maximum value of 0.58 and 0.78 for constraint heights H = 1.0 and 1.2 m, respectively. These findings provide not only fundamental data of pedestrian movement with height constraints, but also new insights into the complex pedestrian movement features in an emergency.