Investigation of pedestrian speed in formation evacuating in two specific water depths

The implementation of a well-organized formation for evacuation plays a critical role in ensuring the safety of individuals during flood events. To investigate the effectiveness of formation evacuating, this study conducted experiments under two specific water depths (0.35 m up to the knee and 0.60 m above the knee). The efficiency of two common evacuation methods, namely single-file formation without a rescue rope (referred to as "without rope") and single-file formation with a rescue rope (referred to as "with rope"), was discussed through questionnaire and trajectory analysis. The findings indicate that the majority of pedestrians (over 60 %) perceive a reduced level of fatigue in single-file formation compared to individual walking (referred to as "individual") in both 0.35 m and 0.60 m water. Not only was the fatigue level the lowest, but it also exhibited the highest speed growth rate in "with rope". Specifically, pedestrian speed increased by 11.24 % in 0.60 m water and by 4.85 % in 0.35 m water compared to "individual". Analysis of pedestrian step characteristics revealed that the increase in pedestrian step frequency was the primary factor contributing to the speed increase in "with rope". Moreover, the step length and step frequency of pedestrians were effectively harmonized in "with rope", particularly in 0.60 m water. Considering factors such as fatigue level and evacuation speed, it is evident that single-file formation evacuating with rescue rope significantly improves evacuation efficiency. This study provides fundamental data and offers practical recommendations for the development of effective flood evacuation strategies.