Columbia subject headings:
Local transit--Security measures--United States.
London Terrorist Bombings, London, England, 2005.
Terrorism--United States--Prevention.
Harvard subject headings:
Local transit--Security measures--United States.
London Terrorist Bombings, London, England, 2005.
Terrorism--United States--Prevention
Princeton subject headings:
Local transit--Security measures--United States.
London Terrorist Bombings, London, England, 2005.
Terrorism--United States--Prevention.