Crowd behavior

Over 1,000 volunteers - students, workers and housewives - gather in a room. Every participant is wearing a white hat with a beer-coaster size QR-code attached to it. Cameras placed above the group record each participant's every move.

Researchers from the Jülich Research Center (Forschungszentrum Jülich) want to understand crowd behavior better and depict it mathematically. Their goal is to increase safety at large events - soccer games, concerts or pilgrim walks - where mass panic has often led to injury and deaths.

How many people fit in an area?

For three days, participants push through corridors and squeeze into the smallest rooms of the halls at the Düsseldorf Trade Fair grounds. Claustrophobes are not welcome. Apart from having to wear a hat with a QR Code, participants also have to wear a red or yellow wristband.

After project leader Armin Seyfried sends the participants through four doors into one of the rooms, his colleague Stefan Holl directs those wearing red wristbands to leave via the exit with the red light. Those with the yellow ones need to leave via the exit with the yellow light.

Participants run in every direction. It takes only a moment for the room to empty out. From above, computer scientist Maik Boltes tracks the chaos with some 30 cameras. This is crucial because the crowd is very dense.

"Because of the small amount of space, some people would be obscured if we didn't use cameras looking down on the crowds," Boltes says.

White hats turn into colorful spots

Using the codes in their hats, Boltes is able to identify each participant. Before beginning the experiment, every participant had to fill in a questionnaire – they had to give their gender, weight or any other information that could influence their behavior.

"From that, you are able to see how smaller people behave. And whether women behave differently from men," Boltes explains.

He also watches how the whole group behaves. And for that, each participant had to say whether he would be in a group in the experiment.

"How do such groups run through a crowd? Do they run next to each other or are they entangled?" Boltes asks.

On the computer screen, the white hats turn into colorful dots.

"A red patch shows where someone is standing. Green means they are moving," explains physicist Armin Seyfreid.

"So you can identify where the [crowd] congestion is, how long the congestion will last and how big it is," he adds.

People who are moving need more space than those who are standing. Therefore, the computer displays them as ellipses. Since it is easier for more people to move if they are next to each other rather than behind each other, the researchers are taking into consideration the length of the legs, according to Seyfried.

Creating models

The goal is to understand how crowd congestion develops and how that can be prevented - for example, by making changes to buildings during construction or by using signs intelligently, says civil engineer Stefan Holls, while asking, "how wide to exits and alley have to be? How much space is needed to be able to cope in possible jam?"

This information is able to assist when building train stations and planning major events like fairs, concerts and sporting events. Seyfried says that at the end of the project he wants to have concrete information that will be able to assist architects, organizers, the police and fire departments.

Computer simulation for architects and exhibitors

"You can think of it as a computer game that is able to map large masses of people in buildings," says project leader Seyfreid.

With it, exhibitors are able to simulate what would happen when 10,000 people all move in the same direction.

"It can come to a point where situations like this get dangerous. Then you have to discard the plan and find an alternative," the physicist adds.

"If you don't take warnings seriously, and there is a rush of people, then it's usually too late," Seyfreid warns.

You can try to direct the people to the emergency exit using a loud speaker, he says, but "at a certain density, it is impossible to reach people. Everything gets lost then. In a crush, you can't comprehend what's going on one or two meters from you."

The experiment in the halls of the Düsseldorf Trade Fair grounds ends well. The participants are in a good mood - they had fun. And it's not over yet. They have to march in again - for the next scramble in the service of science.