Autonomous vehicles, which would carry out many or all of their functions without the intervention of a driver, may bring sweeping social and economic changes in their wake. The elderly, disabled Americans, urban residents, and those who do not own a car may have new travel options. Travel on public roads and highways could become less congested. Highway travel could become safer as well: U.S. roadway fatalities rose in 2015 and 2016, the first annual increases in more than 50 years, and a study by the National Highway Traffic Safety Administration (NHTSA) has shown that 94% of crashes are due to human errors, which autonomous vehicles could reduce. As a U.S. Department of Transportation (DOT) report noted, highly automated vehicles "hold a learning advantage over humans. While a human driver may repeat the same mistakes as millions before them, a [highly automated vehicle] can benefit from the data and experience drawn from thousands of other vehicles on the road." Congressional committees have held numerous hearings on federal policy regarding automated vehicles, and have debated changes in federal regulation to encourage vehicular innovation while protecting passenger safety. In July 2017, the House Energy and Commerce Committee unanimously ordered to be reported the first major legislation on autonomous vehicles ( H.R. 3388 ); the House of Representatives passed that legislation by voice vote on September 6, 2017. The Senate Committee on Commerce, Science, and Transportation reported S. 1885 on November 28, 2017. However, since the House vote and the Senate committee consideration, several accidents involving autonomous vehicles operating under test conditions have raised new questions about how federal and state governments should regulate vehicle testing and the introduction of new technologies into vehicles offered for sale. The technologies used in autonomous vehicles are very different from the predominantly mechanical, driver-controlled technology of the 1960s, when the first federal vehicle safety laws were enacted. Increasingly, vehicles can be controlled through electronics with little human involvement. Performance can be altered via over-the-air software updates. A range of advanced driver assistance systems is being introduced to motor vehicles, many of them bringing automation to vehicular functions once performed only by the driver. These features automate lighting and braking, connect the car and driver to the Global Positioning System (GPS) and smartphones, and keep the vehicle in the correct lane. Three forces drive motor vehicle innovation technological advances enabled by new materials and more powerful, compact electronics; consumer demand for telecommunications connectivity and new types of vehicle ownership and ridesharing; and regulatory mandates pertaining to emissions, fuel efficiency, and safety. Increasingly, such innovations are being combined as manufacturers produce vehicles with higher levels of automation. Vehicles do not fall neatly into the categories of "automated" or "nonautomated," because all of today's motor vehicles have some element of automation. The Society of Automotive Engineers International (SAE), an international standards-setting organization, has developed six categories of vehicle automation—ranging from a human driver doing everything to automated systems performing all the tasks once performed by a driver. This classification system ( Table 1 ) has been adopted by DOT to foster standardized nomenclature to aid clarity and consistency in discussions about vehicle automation and safety. Vehicles sold today are in levels 1 and 2 of SAE's automation rating system. Views differ as to how long it may take for full automation to become standard. Some forecast market-ready autonomous vehicles at levels 3 to 5 within five years. Others argue that it will take much longer, as more testing, regulation, and policy work should be done before autonomous vehicles beyond level 2 are widely deployed. Technologies that could guide an automated vehicle ( Figure 1 ) include a wide variety of electronic sensors that would determine the distance between the vehicle and obstacles; detect lane markings, pedestrians, and bicycles; park the vehicle; use GPS, inertial navigation, and a system of built-in maps to guide the vehicle direction and location; employ cameras that provide 360-degree views around the vehicle; and use dedicated short-range communication (DSRC) to monitor road conditions, congestion, crashes, and possible rerouting. These technologies are being offered in various combinations on vehicles currently on the market, as manufacturers study how to combine them in vehicles that could safely transport passengers without drivers. While private-sector development has focused on vehicle equipment, federal and academic researchers, along with industry, have spent over a decade developing complementary sensor technologies that could improve safety and vehicle performance. These include vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) capabilities—often referred to with the composite term V2X. V2X technology relies on communication of information to warn drivers about dangerous situations that could lead to a crash, using dedicated short-range communication to exchange messages about vehicles' speeds, braking status, stopped vehicles ahead, or blind spots to warn drivers so they can take evasive action. V2X messages have a range of 300 meters (a fifth of a mile)—up to twice the distance of onboard sensors—cameras, and radar. These radio messages can "see" around corners and through other vehicles. NHTSA has evaluated V2X applications and estimates that just two of them could reduce the number of crashes by 50%: intersection movement assist warns the driver when it is not safe to enter an intersection, and left turn assist warns a driver when there is a strong probability of colliding with an oncoming vehicle when making a left turn. V2V communications may also permit technologies such as forward collision warning, blind spot warning, and do-not-pass warnings. NHTSA estimated in 2014 that installing V2V communications capability will cost about $350 per vehicle. DOT has issued two reports on federal regulatory issues with regard to autonomous vehicles, based on consultations with industry, technology and mobility experts, state governments, safety advocates, and others. DOT anticipates that it will continue to issue annual updates on federal regulatory guidance, in light of the pace of autonomous vehicle innovation. The first report issued by DOT, Federal Automated Vehicles Policy , laid the foundation for regulation and legislation by clarifying DOT's thinking in four areas a set of guidelines outlining best practices for autonomous vehicle design, testing, and deployment; a m odel s tate p olicy that identifies where new autonomous vehicle-related issues fit in the current federal and state regulatory structures; a streamlined review process to expedite requests for DOT regulatory interpretations to spur autonomous development; and identification of new tools and regulatory structures for NHTSA that could aid in autonomous deployment, such as expanded exemption authority and premarket testing to assure that autonomous vehicles will be safe. The 2016 guidelines identified 15 practices and procedures that DOT expected manufacturers, suppliers, and service providers—such as Uber and Lyft ridesourcing companies—to follow in testing autonomous vehicles. It was expected that the data generated from this research would be widely shared with government and the public while still respecting competitive interests. Manufacturers, researchers, and service providers were urged to ensure that their test vehicles meet applicable NHTSA safety standards and that their vehicles be tested through simulation, on test tracks, or on actual roadways. To assist in the regulatory oversight, NHTSA requested each entity testing autonomous vehicles to submit Safety Assessment letters that will outline how it is meeting the guidelines, addressing such issues as data recording, privacy, system safety, cybersecurity, and crashworthiness. DOT specified that vehicle software must be capable of being updated through over-the-air means (similar to how smartphones are currently updated), so improvements can be diffused quickly to vehicle owners. Any vehicle operating on public roads is subject to dual regulation by the federal government and the states in which it is registered and driven. Traditionally, NHTSA has regulated auto safety, while states have licensed automobile drivers, established traffic regulations, and regulated automobile insurance. DOT's 2016 report clarified and restated that division of responsibilities for the transition to fully autonomous vehicles with the automobile itself being the driver. The model state policy, developed by NHTSA in concert with the American Association of Motor Vehicle Administrators and other safety advocates, suggested state roles and procedures, including administrative issues (designating a lead state agency for autonomous vehicle testing), an application process for manufacturers that want to test vehicles on state roads, coordination with local law enforcement agencies, changes to vehicle registration and titling, and liability and insurance. Liability may change significantly with autonomous vehicles, as states will have to reconsider the extent to which vehicle owners, operators, passengers, vehicle manufacturers, and component suppliers bear responsibility for accidents when no one is actively driving the vehicle. In addition to its existing authority to issue federal vehicle safety standards and order recalls of defective vehicles, NHTSA has other tools it can use to address the introduction of new technologies: letters of interpretation, exemptions from current standards, and rulemakings to issue new standards or amend existing standards. NHTSA uses letters of interpretation when it receives requests seeking clarifications of existing law. It may take NHTSA several months or even years to issue a letter of interpretation, which cannot make substantive changes to regulations. The agency can grant exemptions from safety standards in certain circumstances. They are not granted indefinitely—an exemption may last for two or three years—or for a large number of vehicles. The approval process may take months or years. Rulemaking to adopt new standards or modify existing ones generally takes several years and requires extensive public comment periods. Federal Automated Vehicles Policy identified potential new tools and authorities that could affect the way autonomous vehicles are regulated. These included the following: Premarket safety assurance tools such as premarket testing, data, and analyses reported by a manufacturer to demonstrate that a new vehicle met standards before being deployed on public roads. The report asserted that some of these tools could be used without new statutory authority. Premarket approval authority, as distinct from safety assurance as well as from the self-certification process used for the past 50 years.