Experimental and numerical study of pedestrian dynamics in low and high density conditions

Resumo

The study of pedestrian movement is a fascinating pursuit "per se". After all, everyone has experienced being a pedestrian in the middle of a crowd. In essence, we are all pedestrians. Within the wide variety of areas from which this topic can be studied, pedestrian dynamics has been established as a new scientific discipline that, in a very active way, has been contributing with new knowledge and practical solutions for the management of pedestrian systems. However, due to the inherent complexity of humans and the multi-scale nature of our interactions with the environment, it is often difficult to perform quantitative measurements of how we behave or what determines our movement, thereby limiting our ability to model and control pedestrian flows. To bridge the gap in our understanding of what characterises pedestrian motion, the aim of this thesis has been to strengthen our knowledge of pedestrian systems by studying two diametrically opposite density regimes: (i) The high-density region, taking evacuation processes as a paradigmatic case of such domain, and (ii) The low-density zone, driven by the COVID-19 pandemic and the imposition of safety distance prescriptions. A dual approach has been followed for these studies, closely combining observations in controlled laboratory experiments and computer modelling. This has allowed studying the motion of pedestrians, the nature of their interactions, and the emergence of collective motion patterns. The first stage has been devoted to study room evacuations as a representative example of a high-density scenario. The effect of placing an obstacle on the pressure exerted on the door has been experimentally evaluated for the first time. Paradoxically, although the presence of this physical barrier has proven to reduce the pressure in the door proximities, its positive performance on this point does not cause an improvement in the flow. From a numerical perspective, certain widespread limitations in current numerical models when simulating evacuations have been discussed. On this matter, our numerical approach has considered two fundamental factors: using a non-circular shape for the agents, which has allowed the incorporation of a physically grounded orientational mechanism, and eliminating any long-range force contribution, which is barely crucial in a scenario where physical contacts dominate. With the beginning of the COVID-19 pandemic, regulations that restricted the development of experiments at high densities were imposed. However, these unique circumstances created a rich set of new avenues to explore, namely those related to occupancy limits and the creation of new physical distancing rules. Thus, the effect of imposing safety distance prescriptions on pedestrian dynamics has been investigated, showing how the characteristic variables of a pedestrian system (e.g. density, speed, etc.) affect its compliance. Likewise, the individual and collective performance of pedestrians under these conditions have been studied, providing a representative description of the role that imposing this new social rule may have on pedestrian motion. Finally, we discovered the spontaneous emergence of vorticity in the aforementioned pedestrian system, a self-organising process that was not expected in low-density conditions. Our analysis sheds some light on which factors trigger the emergence of such structures, explaining the importance of physical boundaries and how they play a fundamental role in the occurrence of symmetry-breaking phenomena. As a whole, this research has contributed to a more quantitative study of pedestrian dynamics and opened new research perspectives which can help add new dimensions to the field and expand its horizons.