Formula for Panic: Crowd-motion findings may prevent stampedes discusses what physicists found when they studied human crowd dynamics:
In normal conditions, pedestrians tend to spontaneously fall into ordered patterns, such as lanes going in opposite directions, previous research had shown. As crowds get denser, stop-and-go patterns begin to propagate in waves, as is typical for cars on heavily trafficked highways. But in critical situations — as when cars get into gridlock — people can break out in panics that result in random patterns of motion, similar to the turbulence of water in the wake of a boat. Crowd members can get squeezed and asphyxiated or fall and be trampled.