"The nation's air, land, and marine transportation systems are designed for accessibility and efficiency, two characteristics that make them highly vulnerable to terrorist attack. While hardening the transportation sector from terrorist attack is difficult, measures can be taken to deter terrorists. The dilemma facing Congress is how best to construct and finance a system of deterrence, protection, and response that effectively reduces the possibility and consequences of another terrorist attack without unduly interfering with travel, commerce, and civil liberties. In the 110th Congress, aviation, rail, and transit security have been a major focus of congressional activity. On January 9, 2007, the House passed the Implementing the 9/11 Commission Recommendations Act of 2007 (H.R. 1), which contains provisions, among others, on aviation and cargo security. On March 13, 2007, the Senate passed the Improving America's Security Act of 2007 (S. 4), which is similar but not identical to H.R. 1. At the end of July 2007, the House and Senate passed a conference agreement on H.R. 1 (H.Rept. 110-259) that was signed into law on August 3, 2007 (P.L. 110-53). Aviation security has been a major focus of transportation security policy following the terrorist attacks of September 11, 2001. In the aftermath of these attacks, the 107th Congress moved quickly to pass the Aviation and Transportation Security Act (ATSA; P.L. 107-71) creating the Transportation Security Administration (TSA) and mandating a federalized workforce of security screeners to inspect airline passengers and their baggage."
CRS Report for Congress, RL33512