When the September 11, 2001, attacks destroyed parts of the New York City transit system and the March 11, 2004, commuter rail bombings did the same in Madrid, Spain, the vulnerability of open, accessible public transit systems and their passengers to terrorist acts was cast in sharp relief. Well prior to these attacks, research on terrorism and public transit had shown public transit systems worldwide to be a principal venue for terrorist acts.

Most previous research on transit terrorism has consisted of single or groups of case studies of major terrorist acts and responses to them by police and transit managers. Case studies are especially useful when "how" or "why" questions are being posed, when the investigator has little control over events, and when the focus is on a contemporary...