Seen from above, a swarm of pedestrians looks like an organized army of ants. They dart through crosswalks and down sidewalks, somehow managing to avoid a game of human bumper cars.
Unconsciously, pedestrians are constantly changing their paths to avoid colliding with other people. Researchers were so intrigued with these unwitting actions that they decided to study them.
Led by physicists from Eindhoven University of Technology in the Netherlands, researchers analyzed 5 million pedestrian movements at the Eindhoven train station. They found that people want to keep an average distance of at least 75 centimeters (roughly 29 inches) from other people. The results of the study were published in the journal Physical Review E.
About 9,000 pairs of pedestrian appeared to be on a collision course towards each other. "About 40 pairs of these actually bumped into each other," said study co-author Alessandro Corbetta in a statement. "The remaining pairs adapted their walkways until they were at least 140 cm apart and were therefore able to prevent a collision."
Forces that keep people from colliding
Researchers used a state-of-the-art tracking system to collect the pedestrian trajectories over a six-month period. Using four overhead sensors, they tracked all pedestrians in a specific area. The sensors used an infrared laser to create a black and white "depth image" of the scene. Pedestrian heads were shown as dark gray spots while shoulders were lighter colored. The image allowed researchers to analyze pedestrians and their speed.
“Our sensors work the same way as game consoles that register motion with a bar above your TV," Corbetta said. "These sensors come with strong advantages: they work well even in the dark, and they do not compromise one's privacy. The data acquired involves only depth values represented in gray shades."
The researchers found two "social interaction forces" that play a role in keeping people from colliding. There's a long-distance force based on what pedestrians see and a short-distance force that avoids actual hard contact with another person. "As an effect of these forces, people modify their current paths to prevent collisions," Corbetta said.
In addition to just being fascinating, the research should also be useful. As corresponding editor Michael Schirber points out in Physics, "The results provide needed details on pedestrian-pedestrian interactions that could help architects and engineers design walkways for smoother and safer traffic flow."