This information was gathered from a review of literature, surveys, site visits, and telephone interviews with personnel from transit police and security departments, local police agencies, transit authorities, and Federal law enforcement agencies. Mass transit systems and infrastructure in the United States have figured prominently in four acts of terrorism and extreme violence since 1993. Internationally, the vulnerability of public transportation agencies is even more pronounced. Assessments from the intelligence community indicate that the threat of terrorism directed against subways, buses, and railways has increased in recent years. Terrorist groups have easy access both to transportation targets and to the materials required to assemble and deploy explosive devices capable of catastrophic impact. Survey results confirmed that a sizeable majority of transit police and operations personnel regard terrorism as a serious threat. Survey respondents were most concerned with the identification and possible detonation of explosive devices on their systems, vehicle hijackings, hostage/barricade situations, and the possibility of shootings with multiple victims. Chemical, biological, or nuclear (CBN) threats against their agencies, while deemed important, were perceived as less immediate than those derived from more traditional forms of terrorism involving explosives and firearms. Respondents generally considered urban rail, commuter rail, and rail terminals to be at the greatest risk of being targeted. Recent experience and training have encouraged transit personnel to assume more responsibility for activities to mitigate terrorism and improve related emergency response capabilities. Security programs focus on improved linkages to local, State and Federal law enforcement agencies; heightened awareness training; and the integration of terrorist response and consequence management skills into system emergency procedures. The programs increase the possibility of the prevention and deterrence of terrorist incidents, improve the effectiveness of response if an incident occurs, and maximize the opportunity to organize and cooperate with local, State, and Federal agencies. 4 tables, 16 figures, 17 references, bibliography, 5 appendices