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Mehdi Moussaïd and the wisdom of the crowd


Mehdi Moussaïd, a researcher at the Max Planck Institute in Berlin, has been studying crowd behaviour for 12 years, mainly trying to understand the logic behind pedestrian mobility.

Mehdi Moussaïd is part of a small but growing group of specialists. With unkempt hair, greying temples, a small goatee and lively eyes hidden behind rectangular glasses, the 37‑year-old French – born in Morocco- is a “crowdologist”, with a passion for “crowdoscopy”. Neither terms have made it into the dictionary just yet and, don’t worry, this father of two is not the guru of some Illuminati cult. Moussaïd could more conventionally be called an ethnologist who, for 12 years, has been studying the behaviour and the mobility of crowds. Last January, he even published a book, Fouloscopie, which expands on his blog, Fouloscopie, ce que la foule dit de nous, where he shares his research in humorous, easy-to-understand terms.

Moussaïd’s life has always been shaped by mobility. In 2000, he left his native Morocco to study science at Nantes University in France, before going on to obtain an engineering degree in computer sciences at the local Ecole Polytechnique. After a good deal of travelling and finding his way, he developed a passion for scientific research and, in 2007, applied to the University of Toulouse to do a PhD in crowd behaviour.

Improving pedestrian mobility

A researcher at the Max Planck Institute in Berlin since 2011, Mehdi Moussaïd has worn many hats, including biologist, physicist and psychologist. But his main focus is pedestrian flows. “The idea is to understand the logic behind pedestrians movements in order to adapt cities and build new ones tomorrow by improving traffic efficiency and making it easier for people to walk from A to B,” explains Moussaïd.

During his first experiments, he examined pedestrians’ capacity to collectively coordinate and avoid each other when crossing paths without actually communicating. He noticed that in France, in 95% of cases, two pedestrians facing in opposite directions will each move to their right, before even taking their first step. This varies from country to country. In Asia, people move to the left. “It’s a behavioural rule, a social convention that’s shared by the entire population. Vehicle traffic can have an impact. Often when you drive on the right, you walk to the right, and vice versa. But there are exceptions. Above all, it’s a social norm that you learn from repetition and failure starting at a very young age.”


The same phenomenon can be observed on very busy pedestrianised high streets. People moving in one direction will spontaneously take up half of the available space. This is the result of mimicry and a subconscious collective knowledge of which side to use to avoid running into people. “These ‘pedestrian motorways’ are the result of intelligent, collective, self-organised behaviour because they naturally ensure smooth pedestrian traffic and make it easier to walk around”, says Moussaïd, whose work earned him the 2011 research prize from French daily newspaper Le Monde.


Planning mobility to avoid accidents

Public authorities and private companies could easily use Moussaïd’s work to improve mobility in their cities, analysing factors such as travel habits and pedestrian densities in certain areas. However, they seem more interested in another aspect of “crowdoscopy” generated by mobility – how to ensure safe, smooth flows in situations with high foot traffic, such as music festivals, sports events, pilgrimages, emergency evacuations and even subway corridors. “We try to understand how crowd surges and crushes come about, and provide solutions that minimise the risk of accidents,” says the crowdologist.

Nudges, for example, are regularly used to improve pedestrian traffic flow and prevent accidents. Bollards installed in the middle of very busy public areas, like statues at park entrances, serve a real purpose. “Placing an obstacle in front of an exit reduces friction between pedestrians and prevents bottlenecks. Adapting the environment influences peoples’ behaviour and mobility. Walking crowds always manage to evacuate an area quicker than running crowds.” When faced with dangers such as suspected attacks, people have a strong tendency to copy their neighbours like sheep or fish, creating a surge. “If you arrive at a train station that you don’t know, you’re likely to head in whichever direction the most amount of people go. Mimicry is the reason for a lot of things in crowds,” explains the researcher.

At Mecca, “crowdoscopy” has allowed organisers to implement drastic measures and contain crowd surges and the resulting accidents. There are only one-way roads today, and each pilgrim’s route is pre-defined, making it possible to control pedestrian density and flows with surgical precision. “Planning is key, because the worst situations are bottlenecks. In high density areas, bidirectional flows should be avoided, for example, and parallel one-way traffic is recommended.” But there’s a problem with Mehdi Moussaïd’s love of crowdoscopy – he never stops working. “I think about it all the time because I’m always confronted by it. As soon as I step outside, I start analysing pedestrians’ behaviour…”


* Author of the book Fouloscopie, published in January 2019 by HumenSciences

** Author of the blog Fouloscopie, ce que la foule dit de nous

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