Simulating dynamics of adaptive exit-choice changing in crowd evacuations: Model implementation and behavioural interpretations

https://doi.org/10.1016/j.trc.2019.04.009Get rights and content

Highlights

  • Modelling exit choice changing (adaptation) in crowd evacuation simulating.

  • Implement an econometric choice model for to simulate dynamic adaptive decisions.

  • Using experimental data to quantify how important the module is for simulation accuracy.

  • Numerical analyses to quantify how decision changing affects evacuation efficiency.

  • Intermediate degrees of decision adaptation and follow-the-peer are beneficial to the system.

Abstract

A crucial aspect of simulating crowds’ evacuation processes is that humans can dynamically revisit and change their decisions. While a relatively great deal of attention has been paid by recent studies to modelling directional decision making, the ‘exit decision changing (or decision adaptation)’ phenomenon has been largely overlooked. Here, we quantitatively investigate (I) how important is to include a decision changing module in evacuation simulation models, and (II) whether decision changing is beneficial to evacuation processes. We propose and implement a parsimonious discrete-choice model of decision changing. The model embodies the most influential factors that make an evacuee revise and adapt their choice of exit. This includes the effects of ‘relative queue-size imbalance at exits’, ‘visibility of exits’, ‘social influence’ and ‘inertia (for maintaining initial decisions)’. Results showed that, the inclusion of the decision changing module made a very substantial difference in enhancing the accuracy of the simulation outputs. Simulating exit choices as one-off decisions strictly limited the degree of match that could be achieved between the simulated and experimental outputs (in terms of replicating the observed exit shares and evacuation times) (question I). Further analyses also revealed that an intermediate degree of decision changing is a strategy that most benefits the system. By contrast, the extreme decision-changing strategies (i.e. “no change” and “too many changes”) were found to be suboptimal. Also, while we have observed, in our other studies, that imitative (or the so-called herd-type) behaviour in ‘exit choices’ is invariably detrimental to evacuation systems, here, we observed that when it comes to ‘adapting exit choices’, a moderate degree of imitation (or follow-the-peer) tendency makes the system more efficient (question II).

Introduction

The fact that decision-making behaviour of humans in emergency escape or evacuation scenarios in crowded places is dynamic is well known. However, the characteristics of this dynamic mechanism is not quite well understood in detail. When evacuations happen in crowded spaces, pedestrians make various types of decisions to escape in shortest possible time (Gwynne et al., 2017). A multi-dimensional process of decision-making is a shared characteristic between evacuations of indoor spaces and those of regional and urban areas as highlighted by researchers in both domains (Kobes et al., 2010b, Mesa-Arango et al., 2012, Murray-Tuite and Wolshon, 2013, Pel et al., 2011, Pel et al., 2012). Evacuees in confined crowded spaces often have the possibility to dynamically revisit and update their decisions in response to the changes in their surroundings to ensure that they take the “best” possible strategy given the information available to them. The dynamics of the environment (e.g. the formation and propagation of the congestion) change over time during emergency evacuations and humans do have the ability and motivation to adjust their initial choices in response to those changes in order to improve their strategies. Strategy adaptation can be observed in relation to various aspects of evacuees’ behaviour including local navigation (Antonini et al., 2006a, Heliövaara et al., 2012a), global pathfinding (Kneidl et al., 2013), reaction decisions (Bode and Codling, 2018, Galea et al., 2017), exit direction choices (Bode and Codling, 2013, Duives and Mahmassani, 2012, Ehtamo et al., 2010, Fridolf et al., 2013, Haghani et al., 2015, Kinateder et al., 2018) or choice of speed (Fridolf et al., 2013).

As mentioned above, the existence of this dynamism in evacuation decision-making in complex environments is intuitively acknowledged, but for modelling purposes, it is crucial for the detailed characteristics of this behaviour to be represented in models. Particular questions that need to be taken into consideration to model this phenomenon could be as follows. What are the circumstances that may make an evacuee more likely to revise their initial decisions? What types of decisions are more likely to be updated and what are the factors driving those changes for each level of decision making (i.e. for directional exit choices, or local pathfinding choices, or global pathfinding choices). And most importantly, how can these factors be represented reasonably in numerical simulation models of evacuation (while maintaining the stability of the numerical simulation process that can potentially be affected by making decisions dynamic)?

In this work, we are particularly interested in understanding and quantifying how crucial it is to include an exit choice changing (or exit choice adaptation) feature in simulation models of pedestrian evacuations. We have observed in our past experiments that people do change their directional exit decisions. However, given that inclusion of this modelling layer will impose additional computational load and calibration complexities, we would like to quantify how important it is to model this phenomenon in the first place. Is it not good enough to approximate decisions of simulated evacuees’ as one-off decisions and generate a fixed decision for each simulated agent? What would be the impact of such modelling practice in quantitative terms?

The second central question of this study concerns the topic of behavioural optimisation. One of the end aims of modelling evacuation behaviour is to gain knowledge that can be utilised to facilitate or ‘optimise’ evacuation strategies (Kneidl et al., 2013). While broadly addressed in the context of urban network evacuations (Huibregtse et al., 2011, Murray-Tuite et al., 2012), this topic, behavioural strategy optimisation, constitutes an aspect of research in crowd dynamics that has been overlooked to great degrees (Berseth et al., 2015, Ding et al., 2017, Kou et al., 2013, Lin et al., 2008, Luh et al., 2012, Noh et al., 2016). As the main attention is currently being paid to developing descriptive models (Duives et al., 2013, Ronchi et al., 2014a) behavioural optimisation is not receiving the attention that it requires. Among the body of studies that have looked at the optimisation of evacuation processes, the majority have investigated the problem from an architectural optimisation (Luh et al., 2012, Zhao et al., 2017) or path-planning optimisation perspective (Lin et al., 2008, Noh et al., 2016, Pursals and Garzón, 2009, Vermuyten et al., 2016). In contrast, little attention has been paid to identifying optimal evacuation strategies at the level of individuals which is a major necessity for developing efficient evacuation training and guidelines (Lu et al., 2014). The question of decision changing has practical implications from the behaviour optimisation and evacuation management perspectives. In specific terms, we would like to quantitatively examine how various degrees and kinds of decision adaptation strategy influences evacuation efficiency. The question concerns whether evacuees can benefit from a dynamic decision-making strategy or is it better for them to adhere to their initial choices rather than continuously exploring and considering all available options. And if there is a benefit in choosing a dynamic strategy, how much adaptation would be optimum.

In this work, we specifically focus on adaptive decision-making in exit choices. We propose a relatively parsimonious discrete-choice model of decision changing that embodies the primary factors that influence occupants’ tendency to revise their initial exit decisions. Through full parametrisation, this model is flexibly capable of representing various forms and degrees of decision changing tendency. It also has the capacity to eliminate decision changing or activate it to extreme degrees through proper parameter specification. By implementing this model, we quantify the extent to which the inclusion of this modelling layer can improve prediction accuracy. Using this model, we also generate behavioural findings based on numerical sensitivity analyses on the parameters of this model. Utilising the fact that each model parameter carries tangible behavioural interpretations and reflects certain kind and degree of adaptation tendency, we perform extensive numerical tests to identify the types of decision-changing strategy that can benefit evacuation processes.

Section snippets

Experimental practices

In an earlier survey of the literature (Haghani and Sarvi, 2018a), we identified a substantial imbalance in the existing studies of evacuation modelling in regard to the amount of attention paid to various aspects of the evacuation decision-making behaviour. This concerns both data collection attempts as well as the development of computational methodologies for various levels of decision making. We showed that studies related to evacuees’ exit choice (i.e. tactical levels of decision making)

Model conceptualisation for exit-choice changing

The existing research on exit choice behaviour has identified a broad range of influential factors that explain such decisions including the size of queue at exits, distance to exits (Haghani and Sarvi, 2016b, Lovreglio et al., 2014), angular displacement (Duives and Mahmassani, 2012), social (or peer behaviour) influence (Haghani and Sarvi, 2017b, Kinateder et al., 2018, Kinateder et al., 2014b), exit visibility and general visibility (Cirillo and Muntean, 2013, Fridolf et al., 2013, Guo et

Comparisons with empirical observations

In order to quantify the magnitude of the effect of including a decision-change module in the simulation tool on the accuracy of the simulated modelling outputs, we resorted to two sets of experimental observations. While these experimental scenarios have been performed originally for individual-level analyses of exit choice (a type of analyses that is beyond the scope of this work), we merely used them for their macro-level (or aggregate) outputs in this work. We do not report on the analysis

How important is an exit-choice-changing module?

The outcomes of the comparison between the simulated and observed measurements have been summarised in scatterplots in Fig. 10. We contrast the observed exit shares with the simulated exit shares under the condition where the decision-change module was and was not active (plots 1 and 2, respectively). We also contrast the observed total evacuation times with the simulated total evacuation times while the decision-change module was active and while this feature was disabled (plots 3 and 4,

Conclusions

This work followed two distinct questions in relation to the evacuation behaviour and modelling of crowds. The first question concerned how crucial it is for the evacuation simulation models to represent the dynamic adaptive nature of the evacuees’ decision-making. We examined this question specifically in relation to the exit-choice behaviour. The second question looked at the effect of decision-changing mechanism on the system performance in terms of the total and individual evacuation times.

Discussion

As will be discussed in the followings, calibration of a decision-changing model (when formulated as a choice between “change” and “not change” alternatives) is relatively challenging compared to the calibration of an exit choice counterpart model. As a result, it was crucial in this work to maintain the feature of modelling parsimony in proposing the model and to limit the number of independent variables in the model. This ensures that the model remains calibratable. However, the authors would

Acknowledgements

The authors extend their sincere gratitude to the Associate Editor and three anonymous reviewers for their constructive feedback.

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