Which agency is responsible for the security of the nation’s transportation systems?

The Transportation Security Administration (TSA) is the agency specifically tasked with overseeing the security of the nation’s transportation systems, including airports, airlines, railroads, and other transit methods. Established in response to the September 11 attacks, the TSA implements policies and procedures to ensure the safety of travelers and transportation infrastructure. Their responsibilities include screening passengers and baggage, managing security protocols, and coordinating with various transportation sectors to enhance security measures.

The other agencies mentioned do play significant roles within the transportation system, but their focuses differ. The Federal Aviation Administration (FAA) primarily regulates civil aviation safety and oversees air traffic control, not directly involved in security matters. The Civil Aeronautics Board was dissolved in the 1980s and its functions have been transferred to other organizations, which also does not pertain to the current security framework. Air Traffic Control is responsible for managing the flow of air traffic to ensure safe flight operations, rather than enforcing security measures. Therefore, the TSA stands out as the correct answer because it is solely dedicated to maintaining security across all transportation modalities.