Every year thousands of people come to the city of Pamplona, in north-eastern Spain, for the opportunity to run for their lives as six fighting bulls are released to charge through the town. There are injuries and deaths every year, but the event is of interest to many people. A paper just published in Science describes the insight the event offers into the psychology of panicked crowds.
That is a useful topic to explore. Architects, civil engineers and urban planners must try to work out how people will behave in the event of a disaster like a fire, a flood or a terrorist attack so they can design their creations to avoid potentially deadly collisions. Unfortunately, solid information is hard to come by. Daniel Parisi, the paper's lead author, realized that the Pamplona bull-runs offered the perfect natural experiment.
Dr Parisi and his team went to two different rooftop locations in Pamplona in July 2019, and filmed the runners as the animals were released. Later in the lab, they calculated the speed of the runners, the density (密度) of the crowd, the probability of a runner tripping and falling and the relationship between runner-group density and speed.
Perhaps unsurprisingly, the researchers found that runners picked up speed when the bulls drew near. Less expected was the finding, that the speed of individual runners augmented with the density of the crowd, which was contrary to a long-held assumption in architectural and urban-design circles that people will slow their pace as group density goes up, in order to lower the risk of a collision, which could lead to a fall and, perhaps, injury or death.
It seems that, in the heat of the moment, people pay little attention to the danger of colliding with each other and even accelerate. The responsibility therefore falls upon urban designers to work out how best to plan the construction of future tunnels, bridges and other passages that restrict flow. The only option may well be to make them broad enough.
