A public discussion held recently at City Hall by Art on the Underground, about London journeys shows a good application of simulation of crowds. As you can see in the images below, London Underground studies people's movements through tube stations to see how they can help by regulating passenger flows through the placement of tickets gates and in turn improving the congestion.
The image above shows passenger flow before improving the congestion, simulated using Legion. The green dots are people entering, and red dots people exiting.
The flow improves considerably as can be seen once the ticket gates and hall layout were changed. The congestion is reduced as it provides more of a two lane flow of exiting and entering pedestrians. More details about the public discussion can be found on Going Underground's Blog