Experimental investigation of the stepping dynamics of upstairs walking under time pressure

The stairway plays a crucial role in vertical traffic and emergency evacuation in built environments. Due to the constraint of stair geometry, pedestrians use special stepping strategies which could reduce the traffic efficiency of the stairway and even increases the risks of tripping and slipping, thus it is desirable to conduct an in-depth investigation of the stepping dynamics on the stairs. In this paper, field observations that directly capture leg movements were conducted to explore the stepping behaviors of the pedestrians walking upstairs under time pressure. Experimental results indicate that the variations of travel speed on the stairway be ascribed to the variance of stride length. The gait characteristic parameters including stride length, stride duration, and stride velocity can be universally captured by a multimodal statistical model consisting of t-location-scale-distributions and lognormal distribution. In addition, the bimodal distribution of stride length on stair flights indicates that people have two preferred stepping strategies when walking on stairway steps, i.e., single-step (SS) strategy and double-step (DS) strategy. Moreover, it was found that time pressure could trigger a transition from SS to DS. The DS strategy helps the crowd to speed up and thus contribute to maintaining a sufficient traffic efficiency during peak hours, such as morning office arrival times. These findings will help the research community to better understand gait characteristics on staircases and should be beneficial for safer pedestrian designs.