3.11 Crowd Disasters
47
3.11 Crowd Disasters
Unfortunately, pedestrian flow doesn’t always self-organize in an efficient way.
Sometimes, terrible crowd disasters happen, and hundreds of people may be injured or
killed, even when everyone has peaceful intentions and does not behave aggressively.
How is this possible?
When I got interested in the problem in 1999, crowd disasters were often regarded
as “acts of God” similar to natural disasters that are beyond human control. However,
the root cause of the breakdown of social order in crowds is similar to the reason
behind “phantom traffic jams”. If the density of people gets too high, the flow of
pedestrians becomes unstable. The resulting crowd dynamics can be uncontrollable
for individual people and even for hundreds of security guards. Nevertheless, crowd
disasters can be avoided, if their causes are well enough understood and proper
preparations made.
Crowd disasters have happened since at least Roman times. That’s why building
codes were developed for stadiums, as exemplified by the Coliseum in Rome. The
Coliseum had 76 numbered entrances and could accommodate between 50,000 and
73,000 visitors, who would exit through the same gate through which they had
entered. These rules and the generous provision of exits meant that the Coliseum
could be evacuated within five minutes. Modern stadiums, which generally have a
smaller number of exits, can rarely match this performance.
Despite the frequent and tragic occurrences of crowd disasters in the past, they
continue to happen due to common misperceptions. Media reports often suggest that
crowd disasters occur when a crowd panics, causing a stampede in which people are
crushed or trampled. Therefore, crowd disasters are claimed to be the result of unreasonable or aggressive behavior, with some individuals pushing others relentlessly as
they try to escape. But why would people panic? My colleague Keith Still put it like
this:
“People don’t die because they panic, they panic because they die.”
In fact, studies that I conducted with Illes Farkas, Tamas Vicsek, Mehdi Moussaid,
Guy Theraulaz and others revealed that many crowd disasters have physical rather
than psychological causes.
39 They may occur even if everybody behaves reasonably
and tries not to harm anyone else. Therefore, the common view that crowd disasters
are mostly a result of panic is outdated. I don’t negate that people are in a danger to
be crushed when the inflow of people into a spatially constrained area exceeds the
outflow for an extended period of time. Certainly, a high density crowd can become
life-threatening under such conditions, as more and more people accumulate in too
little space. However, most of the time crowd disasters occur for a different reason.
39 Helbing et al. [26], Moussaïd et al. [27].
47
3.11 Crowd Disasters
Unfortunately, pedestrian flow doesn’t always self-organize in an efficient way.
Sometimes, terrible crowd disasters happen, and hundreds of people may be injured or
killed, even when everyone has peaceful intentions and does not behave aggressively.
How is this possible?
When I got interested in the problem in 1999, crowd disasters were often regarded
as “acts of God” similar to natural disasters that are beyond human control. However,
the root cause of the breakdown of social order in crowds is similar to the reason
behind “phantom traffic jams”. If the density of people gets too high, the flow of
pedestrians becomes unstable. The resulting crowd dynamics can be uncontrollable
for individual people and even for hundreds of security guards. Nevertheless, crowd
disasters can be avoided, if their causes are well enough understood and proper
preparations made.
Crowd disasters have happened since at least Roman times. That’s why building
codes were developed for stadiums, as exemplified by the Coliseum in Rome. The
Coliseum had 76 numbered entrances and could accommodate between 50,000 and
73,000 visitors, who would exit through the same gate through which they had
entered. These rules and the generous provision of exits meant that the Coliseum
could be evacuated within five minutes. Modern stadiums, which generally have a
smaller number of exits, can rarely match this performance.
Despite the frequent and tragic occurrences of crowd disasters in the past, they
continue to happen due to common misperceptions. Media reports often suggest that
crowd disasters occur when a crowd panics, causing a stampede in which people are
crushed or trampled. Therefore, crowd disasters are claimed to be the result of unreasonable or aggressive behavior, with some individuals pushing others relentlessly as
they try to escape. But why would people panic? My colleague Keith Still put it like
this:
“People don’t die because they panic, they panic because they die.”
In fact, studies that I conducted with Illes Farkas, Tamas Vicsek, Mehdi Moussaid,
Guy Theraulaz and others revealed that many crowd disasters have physical rather
than psychological causes.
39 They may occur even if everybody behaves reasonably
and tries not to harm anyone else. Therefore, the common view that crowd disasters
are mostly a result of panic is outdated. I don’t negate that people are in a danger to
be crushed when the inflow of people into a spatially constrained area exceeds the
outflow for an extended period of time. Certainly, a high density crowd can become
life-threatening under such conditions, as more and more people accumulate in too
little space. However, most of the time crowd disasters occur for a different reason.
39 Helbing et al. [26], Moussaïd et al. [27].