Medary.com

For more than four years - steadily, seriously, and with the unsentimental rigor for which we love them - civil engineers have been studying the destruction of the World Trade Center towers, sifting the tragedy for its lessons. And it turns out that one of the lessons is: Disobey authority. In a connected world, ordinary people often have access to better information than officials do.

Here's the report itself:
Occupant Behavior, Egress, and Emergency Communications