You are in a crowded station. In front of you are two possible routes to reach the platform, and you don’t know which one to choose. The person in front of you takes the one on the left, and without thinking, you follow. You don’t know her, you don’t know where she’s going or if she knows the quickest way to get there, and yet you go. Whether you realize it or not, it must have happened to you on several occasions: in fact, this is how we all tend to behave, following a sheep effect that determines authentic “decisional avalanches” that guide pedestrian flows in crowded environments. This is suggested by a study published in Proceedings of the National academy of sciences (Pnas) by a group of researchers from the Eindhoven University of Technology and the University of Ferrara.
The study
To reach this conclusion, the researchers analyzed 100,000 individual trajectories taken by pedestrians in Eindhoven Central Station between 2021 and 2024, where they are recorded by an anonymous high-resolution tracking system. Thanks to millimetric measurements and large-scale statistical analyses, the authors observed that the probability of choosing one of two possible paths increases if the person immediately in front made the same choice. The fundamental detail in this case is that the effect persists even excluding pairs of pedestrians who are traveling together (groups of friends or family).
The explanation
The hypothesis of the authors of the research is that the unconscious choice to follow those who precede us is a cognitive shortcut: in conditions of uncertainty and overcrowding the brain decides that it is easier to proceed by imitation, rather than waste time and resources, to calculate the optimal path to follow.
“In this work we have identified a phenomenon that redefines the way we think about collective decisions in public spaces,” explains Alessandro Gabbana, researcher at the University of Ferrara and associated with the National Institute of Nuclear Physics. “By inserting a term into the mathematical model that represents the imitation of the immediately preceding person, we were able to reproduce the observed data with great precision. This indicates that local interaction between strangers is the dominant factor in route choices in many real conditions.”
The practical application
In a complex and chaotic environment like a railway hub, processing all the information (signage, timetables, distances) requires effort. Copying the choice made by those walking in front of us is therefore much easier, even if this way we often don’t arrive at our destination first. The interesting thing, even on a practical level, is that this small local interaction can transform into a macroscopic collective event. Individual choices can trigger a “decisional avalanche”, that is, a chain reaction that drags dozens of people in the same direction, regardless of the validity of the initial choice.
Why might this discovery prove useful? Understanding how these sequences of sub-optimal choices arise could help prevent the formation of queues and slowdowns in the pedestrian flow of public places, such as stations, airports or stadiums, and therefore design safer and more efficient infrastructures. Knowing that people tend to follow the trail, designers could in fact improve signage, visual cues and the orientation of spaces to reduce the risk of accidents and emergencies, and guide the crowd in the best direction. Ultimately, you just need to know that to move a mass of people, sometimes you just need to convince the one in front.