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People walk alone relatively quickly. Crowd walking slowly. But how does a crowd move when there is, say, a huge bull charging at them? To answer this, scientists analyzed the movement of a crowd of runners while running bulls in Pamplona, Spain, in 2019.
The San Fermín Festival in Pamplona, Spain, hosts the world’s most famous event for running with the bulls. Every morning for a week each year, festival officials send six bulls down a set of narrow, closed streets toward crowds of waiting people.
In 2019, pedestrian dynamics researcher Daniel Baresi, of the Technological Institute of Buenos Aires, attended the festival, although he wasn’t running himself. Instead, Baresi was collecting data from an array of cameras about four or five stories above the road.
Pedestrian dynamics is the science of how crowds move and is useful to anyone who designs or plans spaces such as buildings or streets. Stadium exits that allow people to exit quickly without creating a human traffic jam may do so thanks to insights from pedestrian dynamics.
But there is a gap in the knowledge of scientists. While scientists have a lot of data from crowds that move at walking speed, when it comes to running crowds, there are very few. It’s hard to predict when something will cause people to scramble in the real world. A constant crowd can be dangerous if people start to stumble upon each other.
“In the lab, this kind of experiment with real risk is not ethical,” Parisi said. But this festival is almost like lab conditions.” It is easy to observe the street, the running takes place several times and in the same place, and the urge – the sudden appearance of a burning bull – is a constant motivational force. “So this is not empirical, but it is quasi-experimental because it is repeated in the same conditions over and over again.”
By capturing videos and using software to mark and track the location of each runner, Parisi and his colleagues were able to explore whether scientists could use real-world events like these to seek insights. In doing so, they made two discoveries.
First, Parisi and his team found that while the crowd can be fast or dense at times, there was a combination of speed and intensity that never occurred due to runners stumbling each other and falling. It’s self-evident,” Parisi said. “With limited personal space, you can’t run too fast.”
But the second result was unexpected. While it is traditionally assumed that bulk crowds move quickly and dense crowds are slow, Parisi found that as bulls first approach runners, for a short period of time, the crowd becomes denser and faster. “This is surprising and hasn’t been noticed before,” Parisi said. He points out that this may be somewhat unique to the particular circumstances of the event – people started relatively far apart and steadily, only to be sent scrambling in extreme ways to avoid the bulls. Racers also know to expect bulls, even if they don’t know exactly when they will appear.
the researchers’ paper, published last week in the journal PNAS, shows that with the right technology, researchers in pedestrian dynamics can actually look at this type of festival or extreme event to gain insight into crowds and their behavior, although more work is needed.
“I think the methodology holds some promise,” said Rachel Birney, an urban design researcher at the University of Washington. She said she would view the research as exploratory – it’s a good idea to review any finding using other methods before relying on it – but that kind of research could provide insights for urban designers.
In an email to Inside Science, Carlo Rati, director of the Massachusetts Institute of Technology’s Sensible City Laboratory, said he thinks doing the study while bulls are running is interesting and that “the paper shows how the big data revolution is helping researchers document and describe previously unexplored environments, and shed light on problems that were not quantifiable only a few years ago.”
As for Parisi himself, he was content to observe the contestants without experiencing the event firsthand. “Maybe if I were twenty years younger,” he said, “but not now.” The festival has many other less risky activities to enjoy instead.
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