Following the crowd or avoiding it? Empirical investigation of imitative behaviour in emergency escape of human crowds

When humans escape from a threat in a crowded space, how do they choose the best wayfinding strategy for their survival? This is a decision context in which individuals are heavily exposed to the actions of others; it is thus plausible to assume that they are influenced by the social interactions. It has been suggested by some influential theoretical studies that in emergency escape situations, 'people show a tendency towards mass behaviour, that is, to do what other people do' (Helbing, D., Farkas, I., Vicsek, T., 2000. Simulating dynamical features of escape panic. Nature, 407, 487-490, page 487). However, the validity of this assumption has not come under scrutiny, nor has the role of context-specific factors that may strengthen or weaken the possibility of displaying the so-called herd-type (or imitative) behaviour been adequately understood in this context. Here, we report on novel wayfinding decision experiments that simulated the escape of human crowds from multi-exit spaces. Participants' perceptions of different contributing factors were quantitatively inferred from their observed choices (N = 3015) using econometric modelling methods. Results showed that the direction at which the social interactions (i.e. observing the movements of other evacuees towards different exit alternatives) impacted on individuals' navigational choices depended significantly on the decision maker's knowledge about the attributes of the alternatives chosen by the crowd flows. Contrary to the conventional belief, people's dominant wayfinding strategy was not to copy the escape directions that other people (i.e. the majority) chose. In fact, in a heavily crowded space with little or no choice uncertainty, observing many people choosing a certain exit direction reduced the desirability of that escape route. The assumption of herd-like behaviour does not necessarily apply to all contexts of evacuations and it should be considered in conjunction with the moderating role of context-specific factors, particularly the level of information available to individual evacuees.