MATHEMATICIANS, physicists, computer scientists and engineers all have a role in predicting how crowds might move, but smart policing is key to effective crowd control, experts say.

    The Shanghai stampede on New Year’s Eve illustrated the consequences of an unanticipated change in crowd dynamics.

    Witnesses and victim’s families blamed authorities for failing to limit crowd numbers and claimed too few police were on hand to diffuse a tidal wave of revelers. Government authorities stopped short of a definitive explanation for what prompted the panic, but local officials and police pledged to reconsider crowd management plans and said they may cancel events likely to draw big numbers.

    A dynamic they might consider is how Chinese tend to have a high tolerance for being packed into tight spaces in the first place and have become conditioned to “self-regulate” rather than wait for authorities to direct their movement, according to Van Troi Tran, a specialist in crowd dynamics.

    The Quebec-based researcher drew conclusions about the particularities of Chinese crowds by studying a World Exposition that Shanghai hosted in 2010. The Expo attracted some 73 million visitors over six months — rivaling some of humankind’s biggest migrations — yet the crowds were mostly safe, according to observers who cited unusual levels of patience in packed conditions.

    “The most striking thing I learned and experienced at the Shanghai World Expo was the calmness of the Chinese crowds, or, more precisely, the lack of panic in situations of overcrowdedness,” Tran said in an emailed response to questions.

    But unlike the purpose-built Expo venue or a stadium, which are designed to safely channel crowds, public festivals like Shanghai’s New Year’s Eve celebration introduce unpredictability, he said.

    The street, according to Tran, is “a space that is not necessarily properly designed for large-scale events, where police control takes a much greater weight.”

    Shanghai police didn’t respond to questions from The Wall Street Journal about their preparations and response. Police quoted in local media have highlighted how the department added officers throughout the evening and warned that the Bund was “close to saturation” through its official microblog a few minutes before the stampede.

    But authorities may have been taken by surprise by the big turnout, according to comments from one senior Shanghai policeman, Cai Lixin, broadcast this week by China National Radio: “There were lot of people at the scene. So police could not enter the area swiftly,” he said, adding that it took about five to eight minutes to carry out rescue activities once police realized what was happening.

    Chen Tao, a deputy researcher at the Tsinghua University Institute of Public Safety Research, was quoted in Chinese media Saturday as crediting crowd-control partitions and buffer zones as positive features used during the Expo, while noting such protections were absent on New Year’s Eve.

    Many of the deaths, according to witnesses, occurred on the 17 stone steps linking a street-level plaza with an elevated riverside promenade that offered the most dazzling cityscape views. When both levels got too crowded, the crush prompted some people on the steps to fall, witnesses said.

    (SD-Agencies)