Mass transit systems provide over 9.6 billion passenger trips per year. The U.S. mass transportation fleet is comprised of 144,000 vehicles, of which 56% are buses. In addition, Amtrak operates a nationwide rail transportation network of 22,000 miles of track, and serves 21 million passengers per year at more than 500 stations.

Several mass transit systems often share terminals and other facilities. In general, the smaller transit systems are independently owned and operated. However most agencies are owned and operated by governmental or quasi-governmental organizations. The largest mass transit agencies are located in New York, Chicago, Los Angeles, Washington, Philadelphia and New Jersey.

TSA seeks to advance mass transit and passenger rail security through a comprehensive strategic approach that enhances capabilities to detect, deter, and prevent terrorist attacks and respond to and recover from attacks and security incidents, should they occur. TSA's strategic priorities for mass transit and passenger rail security are:

• Focus efforts to mitigate high consequence risk to transit assets and systems, particularly underwater and underground infrastructure;
• Expand employment of random, unpredictable deterrence; and
• Build security force multipliers with training, drills and exercises, and public awareness

These strategic priorities are guided by five principles:

• Expanding Partnerships for Security Enhancement
• Advancing the Security Baseline
• Building Security Force Multipliers
• Leading Information Assurance
• Mitigating High Consequence Risks

The only regulatory authority that TSA has exercised in the mass transit industry was in May 2004. Security Directives RAILPAX-04-01 and RAILPAX-04-02 required rail transportation operators to implement certain protective measures, to report potential threats and security concerns to TSA, and to designate a primary and alternate security coordinator. A Notice of Proposed Rulemaking published in December 2006 promulgates the latter two requirements and details TSA's inspection authority in passenger rail.

TSA Surface Transportation Security Inspectors, from the TSA Office of Security Operations, conduct on-site inspections of mass transit and passenger rail agencies and maintain collaborative working relationships with industry representatives. They work closely with the TSA Mass Transit Security Division for support and programmatic direction.