A safe and secure aviation system is a critical component to securing the nation’s overall physical infrastructure and maintaining its economic vitality. Billions of dollars and a myriad of programs and policies have been devoted to achieving such a system. Critical to ensuring aviation security are screening checkpoints, at which screening personnel check over 2 million individuals and their baggage each day for weapons, explosives, and other dangerous articles that could pose a threat to the safety of an aircraft and those aboard it. All passengers who seek to enter secure areas at the nation’s airports must pass through screening checkpoints and be cleared by screeners. In addition, many airline and airport employees, including flight crews, ground personnel, and concession vendors, have to be cleared by screeners. At the nation’s 429 commercial airports that are subject to security requirements, screeners use a variety of technologies and procedures to screen individuals. These include x-ray machines to examine carry-on baggage, metal detectors to identify any hidden metallic objects, and physical searches of items, including those that cannot be scanned by x-rays, such as baby carriers or baggage that has been x-rayed and contains unidentified objects. In response to the terrorist attacks of September 11, 2001, the Federal Aviation Administration (FAA) and the air carriers implemented new security controls to improve security. These actions included increased screening of baggage and passengers at airport checkpoints with the use of explosives trace detection devices and hand-held metal detectors, the mandatory removal of laptop computers from carrying cases, and the removal of shoes. They included additional screening of randomly selected passengers at an airline’s boarding gate. Although these initiatives have been a visible sign of heightened security procedures, they have also, in some instances, caused longer security delays, inconvenienced the traveling public, and raised questions about the merits of using these techniques on assumed lower-risk travelers, such as young children. Congress has also taken actions to improve aviation security. In November 2001, it passed the Aviation and Transportation Security Act, which transferred aviation security from FAA to the newly created TSA and directed TSA to take over responsibility for airport screening. The Act also left to TSA’s discretion whether to “establish requirements to implement trusted passenger programs and use available technologies to expedite security screening of passengers who participate in such programs, thereby allowing security screening personnel to focus on those passengers who should be subject to more extensive screening.” In response to this Act, officials representing aviation and business travel groups have proposed developing a registered traveler program. Under their proposals, travelers who voluntarily provide personal information and clear a background check would be enrolled as registered travelers. These participants would receive some form of identification, such as a card that includes a unique personal characteristic like a fingerprint, which they would use at an airport to verify their identity and enrollment in the program. Because they would have been prescreened, they would be entitled to different security screening procedures at the airport. These could be as simple as designating a separate line for registered travelers, or could include less intrusive screening. Although TSA had initially resisted such a program because of concerns that it could weaken the airport security system, it has recently changed its position and has begun assessing the feasibility and need for such a program and considering the implementation of a test program. The concept underlying a registered traveler program is similar to one that TSA has been studying for transportation workers—a Transportation Worker Identity Credential (TWIC)—that could be used to positively identify transportation workers such as pilots and flight attendants and to expedite their processing at airport security checkpoints. TSA had been studying the TWIC program for several months. Initially, the agency had planned to implement the TWIC program first, saying that any registered traveler program would be implemented after establishing the TWIC program. In recent months, congressional appropriations restrictions have caused TSA to postpone TWIC’s development. According to a senior agency official, however, TSA was still planning to go forward with studying the registered traveler program concept. Although most of the 22 stakeholders we interviewed supported a registered traveler program, several stakeholders opposed it. Our literature review and supporters of the program whom we interviewed identified two primary purposes for such a program—improving the quality and efficiency of airport security and reducing the inconvenience that some travelers have experienced by reducing uncertainties about the length of delay and the level of scrutiny they are likely to encounter. The literature we reviewed and more than a half-dozen of the 22 stakeholders we contacted suggested that such a program could help improve the quality and efficiency of security by allowing security officials to target resources at potentially higher risk travelers. Several stakeholders also indicated that it could reduce the inconvenience of heightened security measures for some travelers, thus encouraging Americans to fly more often, and thereby helping to improve the economic health of the aviation industry. Representatives of air traveler groups identified other potential uses of a registered traveler program that were not directly linked to improving aviation security, such as better tracking of frequent flier miles for program participants. Many of the 22 stakeholders we contacted and much of the literature we reviewed identified the improvement of aviation security as a key purpose for implementing a registered traveler program. Such a program would allow officials to target security resources at those travelers who pose a greater security risk or about whom little is known. This concept is based on the idea that not all travelers present the same threat to aviation security, and thus not everyone requires the same level of scrutiny. Our recent work on addressing homeland security issues also highlights the need to integrate risk management into the nation’s security planning and to target resources at high-priority risks. The concept is similar to risk- based security models that have already been used in Europe and Israel, which focus security on identifying risky travelers and more appropriately matching resources to those risks, rather than attempting to detect objects on all travelers. For example, one study suggested that individuals who had been prescreened through background checks and credentialed as registered travelers be identified as low risk and therefore subjected to less stringent security. This distinction would allow security officials to direct more resources and potentially better screening equipment at other travelers who might pose a higher security risk, presumably providing better detection and increased deterrence. In addition, several stakeholders also suggested that a registered traveler program would enable TSA to more efficiently use its limited resources. Several of these stakeholders suggested that a registered traveler program could help TSA more cost-effectively focus its equipment and personnel needs to better meet its security goals. For example, two stakeholders stated that TSA would generally not have to intensively screen registered travelers’ checked baggage with explosives detection systems that cost about $1 million each. As a result, TSA could reduce its overall expenditures for such machines. In another example, a representative from a major airline suggested that because registered travelers would require less stringent scrutiny, TSA could provide a registered traveler checkpoint lane that would enable TSA to use fewer screeners at its checkpoint lanes; this would reduce the number of passenger screeners from the estimated 33,000 that it plans to hire nationwide. In contrast, several stakeholders and TSA officials said that less stringent screening for some travelers could weaken security. For example, two stakeholders expressed concerns that allowing some travelers to undergo less stringent screening could weaken overall aviation security by introducing vulnerabilities into the system. Similarly, the first head of TSA had publicly opposed the program because of the potential for members of “sleeper cells”—terrorists who spend time in the United States building up a law-abiding record—to become registered travelers in order to take advantage of less stringent security screening. The program manager heading TSA’s Registered Traveler Task Force explained that the agency has established a baseline level of screening that all passengers and workers will be required to undergo, regardless of whether they are registered. Nevertheless, a senior TSA official told us that the agency now supports the registered traveler concept as part of developing a more risk- based security system, which would include a refined version of the current automated passenger prescreening system. While the automated prescreening system is used on all passengers, it focuses on those who are most likely to present threats. In contrast to a registered traveler program, the automated system is not readily apparent to air passengers. Moreover, the registered traveler program would focus on those who are not likely to present threats, and it would be voluntary. Some stakeholders we contacted said that a registered traveler program, if implemented, should serve to complement the automated system, rather than replace it. According to the literature we reviewed and our discussions with several stakeholders, reducing the inconvenience of security screening procedures implemented after September 11, 2001, constitutes another major purpose of a registered traveler program, in addition to potentially improving security. The literature and these stakeholders indicated that participants in a registered traveler program would receive consistent, efficient, and less intrusive screening, which would reduce their inconvenience and serve as an incentive to fly more, particularly if they are business travelers. According to various representatives of aviation and business travelers groups, travelers currently face uncertainty regarding the time needed to get through security screening lines and inconsistency about the extent of screening they will encounter at various airports. For example, one stakeholder estimated that prior to September 11, 2001, it took about 5 to 8 seconds, on average, for a traveler to enter, be processed, and clear a security checkpoint; since then, it takes about 20 to 25 seconds, on average, resulting in long lines and delays for some travelers. As a result, travelers need to arrive at airports much earlier than before, which can result in wasted time at the airport if security lines are short or significant time spent in security lines if they are long. Additionally, a few stakeholders stated that travelers are inconvenienced when they are subjected to personal searches or secondary screening at the gates for no apparent reason. While some stakeholders attributed reductions in the number of passengers traveling by air to these inconveniences, others attributed it to the economic downturn.