David Sim

In an approach based both on cognitive sciences and the physics of complex systems that closely combines experimentation and modeling, SFI External Professor Dirk Helbing and collaborators have created a model that simulates, using a few simple rules, the collective behavior of crowds of pedestrians.

Their model, published in PNAS on April 18, enables them to predict potentially dangerous situations and propose ways to avoid them. It could help urban planners or engineers who design public spaces such as pedestrian malls, stadiums, or concert halls or assist event planners, they suggest. 

Past models of crowd dynamics typically were based on analogies with physicochemical systems. The behavior of individual was formalized using a combination of the forces attracting him to his destination and the forces repelling him from other individuals and obstacles. Such models are difficult to calibrate and only imperfectly reflect reality.

The new model suggests that a pedestrian seeks to minimize congestion in his field of vision by moving towards empty spaces while adjusting his speed to maintain an adequate distance from visible obstacles. Simulations using this model have demonstrated that these two simple rules are sufficient to reproduce a broad range of the collective behaviors observed in crowds, such as the formation of pedestrian lanes or the emergence of a potentially dangerous accordion-style mash-up. Above a critical density, a combination of these rules can result in dangerous collective crushes.

Read the PNAS paper (April 18, 2011)

Read the USA Today article (April 19, 2011)

Read the PhysicsWorld.com article  (April 21, 2011)

Read the MIT Technology Review article (April 20, 2011)

Read the Eurasia Review article (April 22, 2011)

Read the ETH Life article