Evacuation Experiments under Different Visibility Conditions: Investigating Differences Between Individuals and Groups

Crowd is simplified as a collection of single individuals in many existed evacuation literatures. However, most of pedestrians actually move as social groups (e.g. family, friends, colleagues) and the existence of groups in crowd should not be neglected. In this paper, evacuation experiments were conducted in a room under various visibility levels. The fact that crowd contains individuals as well as groups is taken into account. Relationships among participants are investigated by SNA method. Quantitative and qualitative data including pre-movement time, travel time, moving speed and trajectories are analyzed and discussed. The experimental results show that travel time during evacuation is positively correlated with spatial locations, while pre-movement time depends largely on pedestrians' characteristics. The moving forms of groups have advantage over individuals when visibility is low. The pre-movement stage for groups is longer than individuals, but the travel speed for the former is faster than the latter under the worst visibility. Pedestrian's moving trajectory is zigzag bending curve in view-limited condition and its fluctuation degree increases with reduced visibility. Moreover, trajectories in group experiments have less fluctuations and the scope of moving area is larger than that in individual experiments. It is implied that evacuees hold a more stable mental state when moving in groups than evacuating individually. Group behaviors increase the possibility to actively explore information as well as space during evacuation in bad visibility.