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Homeland Security

Threats to Public Transit

The diversity of assets that may be part of a transit system leads to a range of possible threats and countermeasures. Some assets might be targets for a terrorist attack intended to inflict civilian injuries; others might be means for providing misinformation to the public, others for crippling mobility or economic activity within a city or metropolitan area or even for obtaining sensitive information about the system. Transit systems or their components could also be affected indirectly by an attack elsewhere, which may compromise communications, operations, or maintenance capabilities.

Results of attacks or incidents might include:

  • Loss of life or physical injury to transit riders, staff, and/or passers-by
  • Physical damage to transit agency equipment or infrastructure, and possibly to the surrounding environment
  • Loss of power through direct attack or by external event
  • Failures outside the transit agency that affect operations - service delivery or maintenance
  • Excessive traffic on communications networks Breach of communications or operations network security/hacking

While the threat against transit targets is only now gaining broad recognition, transit systems and railways have long been considered viable targets by terrorists. Throughout the 1980s public transit systems were targeted by some terrorists with the intention of inflicting heavy casualties, while others employed more subtle tactics aimed at disrupting transit service. Threats may result in attacks aimed directly at the transit agency, or those aimed at the environment within which an agency operates.


The hazards of arson, an intentionally set fire, in a transit facility include the destruction of assets within the facility, structural damage to the facility itself, and injuries or fatalities due to direct exposure to fire or to smoke and fumes. In a major fire, ambient temperature can surpass 1,800F (1,000C), which may result in structural damage, as well as electrical and mechanical systems failure. Burning fuel, oil, plastics, and some paints can cause dense smoke and toxic fumes.

Toxic fumes present a serious health threat and may cause death by asphyxiation. In addition, smoke can reduce visibility, obscuring exit pathways and making escape more difficult for victims. Since fires may occur accidentally as well as intentionally, there is crossover between protection against accidental fires and protection from arson. Arson and explosion-related fires, however, may cause more severe damage because they tend to target or cluster around critical systems and equipment.


The hazards of an explosive blast include the destruction of assets within a facility, structural damage to the facility itself, and injuries or fatalities. In addition, explosions may start a fire, which may inflict additional material damage, injuries, or fatalities due to direct exposure or to heat, smoke, and fumes. An explosion is an instantaneous or almost instantaneous chemical reaction resulting in a rapid release of energy. The energy is usually released as rapidly expanding gases and heat, which may be in the form of a fireball.

The expanding gases compress the surrounding air creating a shock wave or pressure wave. The pressure wave can cause structural damage to the structure while the fireball may ignite other building materials leading to a larger fire. The strength of a blast depends on the type and amount of explosive material used. A bomb that a person can carry is capable of a smaller blast than an explosive-laden truck.

Weapons of Mass Destruction

Weapons of mass destruction (WMD) typically refer to nuclear, radiological, chemical, and biological weapons capable of inflicting mass casualties. WMD can also refer to radioactive materials and other contaminants intended to quickly harm large numbers of people, such as any powders, liquids, gases, and dirty bombs; most of these come in a liquid, vapor, gas, or powder form, and are spread through air movement.

The hazards of WMD include fatalities or deleterious health effects, as well as potentially permanent contamination of a facility that may render it unusable. Many agents have little or no plainly discernable characteristics, so symptoms may be the first sign that an attack has occurred. While some chemical agents induce immediate symptoms, other agents will not produce symptoms for hours after the attack. Some biological agents may have an incubation period of up to a few days before symptoms appear.

Violent Incidents and Hostage Situations

Violent confrontations by terrorists are common on transit systems throughout the world. These include assaults carried out on board transit vehicles or at transit facilities, with the intent of inflicting casualties, property damage, or both. Violent incidents may include the taking of hostages. Transit vehicles are especially vulnerable to hostage situations because of easy public access, remoteness of the vehicle, and available civilians onboard.

Such attacks are meant to create widespread fear and apprehension through public displays of violence and the interruption of public services. Attackers may use a variety of weapons, including small arms, assault rifles, shoulder-mounted rocket-propelled grenades, knives or other bladed weapons, and small explosives.


Tampering with transit facilities' assets may be a means to achieve any of the above events, such as starting a fire or spreading an airborne chemical agent, or it may be a stand-alone act, such as tampering with track to induce derailment.

It can also include the intentional ramming of a facility, with a truck, boat, or airplane, in order to cause structural damage to a facility or injury to its users. The ramming vehicle may be laden with explosives. Depending on the situation, tampering may lead to asset damage, structural damage, contamination, injuries, and/or fatalities.

Loss of Power

Loss of electrical power, either locally or over a broad area, can pose a major problem for transit systems in the form of diminished or suspended operations control, computer-aided dispatch, and radio systems. Loss of electricity could be the result of an intentional attack or unintentional event-either within the agency or in the surrounding environment-but in any case could hinder a transit agency's ability to operate or communicate effectively.

Apart from service impairment, loss of power may even inadvertently result in damage to property or persons within the agency, service area or in the vicinity.

Transit Vehicle as a Weapon

Transit vehicles should be viewed not only as targets, but as weapons as well. There can be a wide range of nefarious uses for both operational and retired vehicles. Perpetrators might attempt to hijack an operational vehicle in order to steer it into a building or bridge, or may plant explosives in the vehicle while in the storage yard in hopes of detonating it at a later time.

They might also seek to steal or purchase a retired vehicle, counting on the innocuous nature of a public transit vehicle to set people at ease while they carry out various terrorist activities. Attacks might be directed at the vehicle itself, at the transit system, or at the surrounding environment.

Network Failure/Cyber Attack

Transit systems rely on computerized networks to facilitate operations and enhance efficient service delivery, which makes them vulnerable to network failure and cyber attacks. While this document does not offer specific considerations on how to protect computer networks, it is crucial to understand their importance to operating and communicating among agency staff as well as with partner organizations and the public-at-large.

Network failure may be caused by faulty or damaged internal components, direct cyber attack to the agency's network, direct attack to a peripheral system or network, or even a blanket computer virus. The result may be loss of communications or operations capabilities as well as misinformation by hacking into a Web site or server.

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Page last modified: 13-07-2011 12:49:59 ZULU