Accommodating taste heterogeneity and desired substitution pattern in exit choices of pedestrian crowd evacuees using a mixed nested logit model

In this paper, we report on a mixed nested logit application aimed at understanding evacuation behaviour of human crowd, particularly the choice of exit. Evacuees' trade-off between contributing factors are elicited through a data set of stated exit choices. We attempt to improve the realism of the choice experiments by conducting face-to-face interviews with pedestrians (respondents) as they exit a building; and designing scenarios that refer to their recent actual choice of exit. The primary analysis strongly suggests the presence of taste heterogeneity as well as the violation of the IIA assumption (i.e. the presence of a particular pattern of correlation between exit utilities). We propose and estimate a mixed nested logit model through which we accommodate these two econometric aspects of the problem in a unified model. Compared to the counterpart mixed multinomial logit model in which the desired substitution pattern is embodied through specification of the explanatory variables, the proposed model reduces the dimension of simulation in the likelihood maximisation procedure, and also yields a slightly better statistical fit.