How behavioural changes in social groups affect evacuation efficiency of crowds

• Crowd evacuation experiments involving individuals and social groups. • Interventional experiments targeting the physical movement of social groups. • Social groups slow down crowd evacuations, with inefficiency worsening as group size increases. • The inefficiency is attributed to the larger spatial footprint associated with groups. • Forming a platoon significantly reduces inefficiency and accelerates the evacuation process. Consider an incident of acute emergency—such as a violent attack—necessitating swift evacuation of a crowd primarily made up of social groups. Is it possible to identify simple strategies that the groups can implement to facilitate collective movement efficiency? There has been some research, though not extensive, aimed at understanding unique evacuation dynamics of crowds of social groups, but mostly from a descriptive or observational perspective. Here, we introduce and explore a prescriptive or interventional approach. The aim is to establish effective behavioural interventions. Experiments are conducted with crowds of solo individuals as well as crowds composed of groups of three or groups of five. The results demonstrate a clear decrease in evacuation efficiency as crowd composition shifts from solo to groups, with a more pronounced effect observed with larger groups. We demonstrate how this inefficiency is attributable to the larger spatial footprint associated with groups. The findings also reveal that instructing groups to hold hands does not enhance evacuation efficiency. However, instructing them to form a line (i.e., platooning) leads to significant improvements, reducing evacuation times to levels comparable to crowds of solo individuals. These findings suggest that simple and easily communicable behavioural modifications for social groups can have substantial impacts on their evacuation efficiency. Making such strategies common knowledge has the potential of helping more people survive acute crises, an important aspect of collective resilience.