John Robb examines terrorist attack crowd location anticipation as part of attack tactics.

Last August, in a Shiite neighborhood in eastern Baghdad, a suicide car bomb went off near a police station across the street from an open air bus station. Ten minutes later, as people crowded in the station to watch the rescue across the street, another suicide bomber drove his car into the station itself. The carnage was widespread but far from over. Twenty minutes later, as the victims of the first two blasts were removed to Kindi hospital only 200 yards away from the terminal, a third suicide car bomb went off at the hospital's side entrance.

What's interesting to me in this incident is the effort spent by the attackers anticipating where crowds would form. This is clearly a substantial tactical advance over earlier efforts (and like most developments from the proving ground in Iraq, something we are likely to see later). The attackers weren't thinking in terms of a single event but rather a series of events where they controlled the outcome. This series had a synergistic effect that far exceeded the impact of the bombs as single random events. The effectiveness of this attack was seen in how the bus terminal bombing set the expectations (shaped the battlefield) for this later event:

Flash forward 13 days to a bridge over the Tigris packed with Shiite pilgrims marching to a shrine for a religious festival. A rumor that there is a suicide bomber in the crowd created a panic that generated a stampede. 965 people die (in the crush or drowned in the river).

What's disturbing (at least to me) is how this type of "fear management" could be scaled. One area of potential application is the planned disruption of crowds fleeing a city. As we saw in the evacuations from Katrina and Rita, our ability to manage mass evacuations are far from adequate even in a benign environment. In an evacuation due to a dirty bomb or even minor biotoxin release, the outcome could be much worse. In either case, if we had a thinking enemy that has planned a series of events that leverage a rudimentary knowledge of crowd dynamics (as exhibited in the bus terminal incident) to disrupt the evacuation, we would likely have a catastrophe. In this situation (as with most system disruption) the crowd would be used to do damage to itself.

The interstates and highways leading out of many American urban metropolitan centers become jammed during holidays or even summer weekends. I can't imagine the chaos in a cascading crisis similar to those occuring in Iraq presently.