Columbia subject headings:
Infrastructure (Economics)--United States.
National security--United States--Planning.
Terrorism--United States--Prevention.
Transportation--Security measures--United States.
Harvard subject headings:
Infrastructure (Economics)--United States.
National security--United States--Planning.
Terrorism--United States--Prevention
Transportation--Security measures--United States
Princeton subject headings:
Infrastructure (Economics)--United States.
National security--United States--Planning.
Terrorism--United States--Prevention.
Transportation--Security measures--United States.