	Introduction

The nation's air, land, and marine transportation systems are designed for accessibility and efficiency, two characteristics that make them vulnerable to attack. While hardening the transportation sector against terrorist attack is difficult, measures can be taken to deter terrorists. The focus of debate is how best to implement and finance a system of deterrence, protection, and response that effectively reduces the possibility and consequences of terrorist attacks without unduly interfering with travel, commerce, and civil liberties. Aviation Security1

Following the 9/11 terrorist attacks, Congress took swift action to create the Transportation Security Administration (TSA) within the U.S. Department of Transportation and gave it control over all airline passenger and baggage screening functions and deployment of armed air marshals on commercial passenger flights. Despite the extensive focus on aviation security for more than a decade, a number of challenges remain, including
effectively screening passengers, baggage, and cargo for explosives threats; developing effective risk-based methods for screening passengers and others with access to aircraft and sensitive areas; incorporating biometrics into the passenger screening process to verify identities; exploiting available intelligence information and watchlists to identify individuals who pose potential threats to civil aviation; implementing effective systems, regulations, and international agreements to assess risk and conduct risk-based screening of air cargo shipments worldwide; effectively deterring and responding to security threats in public areas of airports and at screening checkpoints; developing effective strategies for addressing aircraft vulnerabilities to shoulder-fired missiles and other standoff weapons; and addressing the potential security implications of unmanned aircraft operations in domestic airspace and developing effective countermeasures to protect critical infrastructure, including airports and aircraft, from attacks using drones. Immediately following the 9/11 attacks, the Aviation and Transportation Security Act (ATSA; P.L. The Transportation Security Acquisition Reform Act ( P.L. The FAA Extension, Safety, and Security Act of 2016 ( P.L. These include PreCheck; modified screening procedures for children 12 and under; and a program for expedited screening of known flight crew and cabin crew members. Nonetheless, it has improved screening efficiency. Plans for increased use of biometrics raise privacy and data-protection concerns that may be of particular interest to congressional oversight committees. TSA requires security background checks of airport workers with unescorted access privileges to secure areas at all commercial passenger airports and air cargo facilities. 114-190 authorized TSA to provide training to foreign governments in airport security measures including the use of canine teams. Transit and Passenger Rail Security37

Bombings of and shootings on passenger trains in Europe and Asia have illustrated the vulnerability of passenger rail systems to terrorist attacks. Passenger rail systems—primarily subway systems—in the United States carry about five times as many passengers each day as do airlines, over many thousands of miles of track, serving stations that are designed primarily for easy access. The surface transportation inspector program has been a focus of congressional interest. Port and Maritime Security49

The bulk of U.S. overseas trade is carried by ships, and thus the economic consequences of a maritime terrorist attack could be significant. In the aftermath of the 9/11 attacks, the U.S. Customs Service (now Customs and Border Protection, CBP) and the Coast Guard realized that they needed to "push the borders out"—that is, they needed to begin screening vessels and cargo before they reached a U.S. port. 115-254 ). Two aspects of maritime security that have drawn attention recently are cybersecurity and the use of drones for coastal surveillance.
The nation's air, land, and marine transportation systems are designed for accessibility and efficiency, two characteristics that make them vulnerable to terrorist attack. While hardening the transportation sector is difficult, measures can be taken to deter terrorists. The enduring challenge facing Congress is how best to implement and finance a system of deterrence, protection, and response that effectively reduces the possibility and consequences of terrorist attacks without unduly interfering with travel, commerce, and civil liberties.
Transportation security has been a major policy focus since the terrorist attacks of September 11, 2001. In the aftermath of those 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 that security screeners employed by the federal government inspect airline passengers, their baggage, and air cargo. Despite the extensive focus on aviation and transportation security over the past decade, a number of challenges remain, including
developing and deploying effective biometric capabilities to verify the identities of transportation workers and travelers; developing effective risk-based approaches to vetting and screening transportation workers accessing secured areas of airports and other sensitive areas of transportation networks; developing cost-effective solutions to screen air cargo and freight without impeding the flow of commerce; and coordination among state, local, and federal homeland security and law enforcement personnel to effectively deter and respond to criminal and terrorist acts targeting public areas of transportation facilities.
The FAA Extension, Safety, and Security Act of 2016 (P.L. 114-190) and the TSA Modernization Act (P.L. 115-254, Division K) included provisions intended to improve screening technologies, streamline the passenger screening process, mandate more rigorous background checks of airport workers, strengthen airport access controls, increase passenger checkpoint efficiency and operational performance, and enhance security in public areas of airports and at foreign airports where flights depart for the United States. Oversight of TSA actions to implement these mandates may be an area of particular interest in the 116th Congress. Particular topics may include the evolution of screening technologies and assessments of emerging screening technology solutions; the expansion of canine teams for transportation security; the expansion of the PreCheck program to expedite screening of known travelers; the use of biometrics and associated data security and privacy concerns; implementing effective approaches, regulations, and international agreements to conduct risk-based screening of air cargo shipments worldwide; protecting public areas of airports; and developing effective countermeasures to protect critical infrastructure, including airports and aircraft, from attacks using drones.
Bombings of passenger trains in Europe and Asia in the past few years illustrate the vulnerability of passenger rail systems to terrorist attacks. Passenger rail systems—primarily subway systems—in the United States carry about five times as many passengers each day as do airlines, over many thousands of miles of track, serving stations that are designed primarily for easy access. Transit security issues of recent interest to Congress include the quality of TSA's surface transportation inspector program. The bulk of U.S. overseas trade is carried by ships, and thus the economic consequences of a maritime terrorist attack could be significant. Customs and Border Protection (CBP) and the Coast Guard have implemented security screening procedures that effectively "push the borders out"—that is, they begin screening vessels and cargo before they reach a U.S. port. Two aspects of maritime security that have drawn attention recently are cybersecurity and the use of drones for coastal surveillance.