Border and Transportation Security (BTS) is a pivotal function in protecting the American people from terrorists and their instruments of destruction. The issue for Congress is how to achieve desired levels of security, while not compromising other important values in the process. In a series of three reports, a strategic approach to BTS using a variety of frameworks to clarify objectives and help identify policy options is discussed. This final report builds on the analysis presented in the first two reports, and explores possible new directions and policy options that spring directly from the analytical frameworks contained in those reports. Before doing so, however, it is useful to place this set of activities in the broader context of overall Homeland Security efforts and to review the development of congressional concern and policy approaches up to this point. The homeland security effort can be seen as a series of concentric circles or screens, with the outer screen being that of preventive efforts launched outside the country. The continuum of activities to provide homeland security then moves through progressively smaller circles starting from more distant efforts to closer and more localized measures. Thus, the process starts with prevention abroad and ends with emergency preparedness and response at home: Discovery and preventive intervention of terrorist actions emanating from abroad before reaching the United States; Interdiction of dangerous people or things at the U.S. border and in the interior transportation sector; Defense against catastrophic terrorism inside the United States through law enforcement and domestic intelligence efforts; Protection of critical infrastructure and the population ; and Emergency Preparedness and response . Congressional concern with terrorism and border security was manifested early, following a series of terrorist attacks in the 1990s. The congressional response began with inquiries as to the nature of the terrorist threat and the commissioning of several studies, and was followed by specific, targeted measures to protect the nation following the events of 9/11. Congressional interest, however, continues in broader, more comprehensive approaches including efforts in the 108 th Congress to respond to the report of the 9/11 Commission embodied in the Intelligence Reform and Terrorism Prevention Act of 2004 (IRTPA, P.L. 108-458 ). Congressional policy actions are summarized briefly below: Broad efforts to understand the terrorist threat . Starting in 1998, Congress stimulated the creation of three commissions to better understand the nature of the terrorist threat facing the nation. These included the Gilmore Commission, the Bremer Commission, and the Hart-Rudman Commission. Highly specific actions to protect against immediate threats . Immediately following the airplane-based attacks of 9/11, early legislative action focused on airline security, visa and border security, and then moved on to maritime security. Structural and procedural changes to provide an effective framework for action . Following the 9/11 attacks, Congress enacted legislation to create the Department of Homeland Security to provide a structural framework for subsequent action, and the USA PATRIOT Act to provide the tools needed for the new challenge to national security. Interest in broader, more comprehensive substantive approaches . As evidenced in oversight hearings, Congress has been frustrated by the failure to more aggressively address other border and transportation security threats (including the need to create integrated terrorist watch-lists, and measures to address other modes of transportation—rail and mass transit, air cargo, trucking, and buses). These concerns were given a strong impetus by the Final Report of the 9/11 Commission, which highlighted the need for more strategic approaches to the terrorist threat, and are now expressed in legislative form in P.L. 108-458 . The evolution of congressional concern (moving from general to specific and back to broader concerns) makes this an opportune time to consider some possible policy frameworks that might shed additional light on the nature of the problem and possible new or enhanced policy choices. The next section of the report briefly summarizes the two earlier reports in the series that address the complexity of the challenge, as well as the programs and policies developed thus far to contribute to border and transportation security. The third section explores the idea of using a "layered" approach to protecting the nation—relying on multiple and overlapping policy actions on a number of fronts to increase the probability of interdicting bad people or bad things. The final section explores some ideas for possible new directions and policy options that spring directly from the analytical frameworks used in the report. The task of providing border and transportation security is complex both because of its scale and possible conflicts with other important national goals. The magnitude of the task is substantial—covering thousands of miles of land borders, millions of passengers, hundreds of airports and seaports, and millions of individual motor vehicles, rail cars, and cargo containers. The first possible goal conflict springs from the demands of security confronting the need for facilitating the essential travel and trade that are at the heart of continued economic growth. This reality leads to a redefinition of the task from one of pitting security vs. economic well-being to that of good border management. Good border management requires facilitating (and even expediting) the flow of desirable goods and people across our borders, while screening out dangerous people and material. The process of doing that is made more manageable if the border is envisioned not merely as a physical boundary but rather as a flexible concept that allows for the possibility that the border begins at the point where goods or people commence their U.S.-bound journey. The result of such a broader perspective is a significantly wider array of options for good border management. A companion report presents several graphical images of how this process might be envisioned. (See CRS Report RL32839, Border Security: The Complexity of the Challenge , by [author name scrubbed].) That report blends the geographic dimension of the problem with the challenge of screening people, goods, and documents. It starts by identifying the paths that may be followed in moving from the source country to the United States, and then overlays the various points at which people, goods, and documents face the possibility of interception en route to the ultimate destination (the final destination inside the United States). The results are portrayed in Figure 1 . The figure should be viewed from left to right, moving from the foreign port of exit (FPOE) through a transit zone (illustrating the case where some goods or people might move through one or more intermediate countries en route), to the domestic port of entry (DPOE)—the final destination in the United States. In the process, exported goods may be handled by multiple intermediaries, people will follow several processes, and the necessary travel documents will pass through many hands. While designed to illustrate the multiple points where bad things can happen, the illustration also suggests that the multiple points of vulnerability in the shipping or travel process can also be seen as opportunities for interception—and, if exploited, can actually increase the probability of interdiction of the bad things and bad people that we seek to intercept before they arrive at their intended targets. The current programs designed to accomplish this interception are discussed more fully in the second report in this series: CRS Report RL32840, Border and Transportation Security: Selected Programs and Policies , by Lisa M. Seghetti, [author name scrubbed], and [author name scrubbed]. These efforts can be summarized by using an analytical framework that highlights generic strategies that might be used to achieve greater border and transportation security: Pushing the border outwards to intercept unwanted people or goods before they reach the United States (as in the Container Security Initiative and passenger pre-screening); Hardening the border through the use of technology (e.g., X-ray machines for examining cargo without opening the containers, radiation and explosives detectors, and unmanned aerial vehicles to monitor remote areas at the border); Making the border more accessible for legitimate trade and travel (faster passage for trusted travelers and cargo conveyors); Strengthening the border inspection process through more effective use of intelligence (terrorist screening data bases); and Multiplying effectiveness of interdiction programs through the engagement of other actors in the enforcement effort (including engaging Canada, Mexico, state and local law enforcement resources, and the private sector). The realization that multiple points of vulnerability might be turned into expanded opportunities for interdiction has given rise to the notion of a "layered" approach to security. The basic idea of layering is that multiple and overlapping measures applied at key points in the border security environment could succeed where only more targeted measures might fail because of their rising expense, increasing conflict with other goals, or inability to cover all conceivable risks arising from opportunistic terrorist tactics. The concept of a layered approach to border and transportation security is gaining currency in policy discussions. The idea was cited in a security context in the so-called Gore Commission Report on aviation safety and security in early 1997. The commission stated the belief that "aviation security should be a system of systems, layered, integrated, and working together to produce the highest levels of protection." An important pre-9/11 reference to "layering" was found in the Hart-Rudman Commission Report in 2001. The commission stated: "We believe that homeland security can best be assured through a comprehensive strategy of 'layered defense' that focuses first on prevention, second on protection, and third on response...." This report discusses the concept of layered protection as applied specifically to border security, and offers a definition that is intended to translate the concept into something more concrete—with the goal of making it possible to be applied to actual programs and policy actions. The most recent advocacy of a layered approach comes from the 9/11 Commission Report issued in July 2004. Addressing the importance of passenger screening, the commission states: "The FAA set and enforced security rules, which airlines and airports were required to implement. The rules were supposed to produce a 'layered' system of defense. This meant that the failure of any one layer of security would not be fatal, because additional layers would provide backup security."