The National Highway Traffic Safety Administration (NHTSA) is proposing to require event data recorders (EDRs)—widely referred to as "black boxes"—on all new passenger vehicles sold in the United States. Although over 90% of the new cars and light trucks sold in the United States already come with EDRs intended to capture information about the final seconds before a crash, these are installed voluntarily by the manufacturers; NHTSA's current rules mainly specify certain types of information that must be recorded if a vehicle is equipped with an EDR. NHTSA's proposed regulation would make EDRs mandatory, but would not substantively change federal requirements about the information the devices must collect. EDRs are not new. Flight data recorders, also widely referred to as "black boxes," have been installed in aircraft since the 1950s and are used after accidents to reconstruct the critical moments of a plane's operations. Event recorders are also in use in railroad locomotives and large cargo and passenger ships. But the mandatory installation of EDRs in passenger cars has been controversial in Congress. While legislators have generally recognized the devices' potential safety value, in passing the Moving Ahead for Progress in the 21 st Century Act in 2012 (MAP-21) , Congress declined to mandate EDRs in new passenger vehicles due to some members' concerns about driver privacy. A proposal to bar the U.S. Department of Transportation (DOT) from using appropriated funds to develop regulations mandating data recorders was passed by the House of Representatives in 2013, but was not enacted. A bill to limit access to EDR data, S. 1925 , was ordered to be reported by the Senate Commerce Committee in April 2014. An EDR is a device installed in a motor vehicle that records certain technical information about a vehicle's operational performance for a few seconds immediately prior to and during a crash. Early versions of EDRs used analog signal processing and recording to analyze and store data and were first tested by NHTSA in the 1970s. The first commercial EDRs were installed by General Motors Corp. (GM) in select models in 1974. EDRs have evolved over the past 40 years as motor vehicles have increasingly come to rely on electronic sensors. Greater energy efficiency was a primary goal of the move to electronics. A key component in the electronics system is the engine control unit (ECU), which collects and analyzes information about the engine's operation, such as throttle position, revolutions per minute, and airflow. Based on these engine variables, the ECU sends instructions to the fuel injectors varying the length of time a fuel injector pulses or specifying how much spark advance the engine receives in order to improve fuel economy. These are among the variables which are recorded by EDRs. But over time, as automakers sought ways to evaluate the sensors and make the new systems easier to service, the role of the ECU was expanded to include a diagnostic component which stored data on problems detected through the sensors. This new source of information was helpful to mechanics attempting to address vehicle performance issues, but also laid the groundwork for data recovery technology. For example, the airbag sensor could store a fault, but also could count the number of times the engine had been started since the fault was generated. An EDR is a small box, which is generally installed under one of the front seats of a vehicle or sometimes in the center console. The EDR is the key electronic component in recording an accident. It accumulates data from a dedicated sensor or, sometimes, from a vehicle network. Passenger vehicle EDRs are usually incorporated within an air bag electronic controller. A crash-sensing algorithm decides within 15-50 milliseconds (msec) after an impact when the airbag should be inflated, based on model-specific criteria stored in a sensor. The algorithm also determines when the pre-crash data will be recorded. As discussed later in this report, a current NHTSA rule specifies that if the vehicle has an EDR, information on 15 data elements must be recorded at the time of a crash. EDRs installed by some manufacturers collect other data not mandated by federal regulations. Among the data points a particular manufacturer's EDR may record are seat track positions, the weight of the occupants of the driver's seat and front passenger seat, and additional detail on air bag deployment. Neither existing nor proposed regulations mandate that such information be recorded, but NHTSA regulations specify what intervals must be recorded if a manufacturer installs a black box designed to collect such data. Information stored is limited only by the amount of available memory in the sensor. Once the crash data are stored on the EDR, they cannot be erased or altered. An exception is a "near-deployment" of the airbag, i.e., an accident which does not set off the airbag. In such cases, the data stored on the sensor are cleared from the memory after 250 ignition cycles (about 60 days on average). The EDR is connected to other sensors, such as the anti-lock brake computer ( Figure 2 ). It collects data from these sensors and continually replaces previously stored data every five seconds. Only the most recent data are retained when airbags are deployed in a crash situation. The data are retrieved by a cable to the EDR or, alternatively, to the vehicle's onboard diagnostic port (known as OBD-II) located near the steering wheel. EDRs in passenger vehicles collect a much more limited range of information than "black boxes" aboard other types of transportation vehicles. For example, flight data recorders aboard aircraft can record hundreds of flight parameters for up to 25 hours, and cockpit voice recorders capture all voices in the cockpit for the duration of a flight. Data recorders in railroad locomotives must preserve information on about 25 different variables over a 48-hour period. EDRs in automobiles have no voice recording capabilities and are not designed to store large volumes of data. The EDR data can be useful in a variety of ways. They may be used by law enforcement agencies to help determine why an accident occurred. They could potentially be used to evaluate a driver's responsibility for a crash. The data are used by automakers to better understand vehicle performance in crash situations, thereby possibly leading to vehicle redesign and safer automobiles. They may also be used by federal, state, and local highway officials to evaluate road conditions and safety configurations that could be improved to mitigate accidents. NHTSA's Special Crash Investigations (SCI) program first used EDR information in a crash investigation in 1991 (in conjunction with GM, which had manufactured the vehicle involved in the crash being reviewed). In the years following, NHTSA worked with automakers to improve understanding of how electronic sensors could contribute to the evaluation of crash conditions. In 1997, the National Transportation Safety Board (NTSB) recommended greater use of EDRs because of their potential to improve highway safety. In 1997, the NTSB recommended that NHTSA "pursue crash information gathering using EDRs" and that it develop and implement, in conjunction with the domestic and international automobile manufacturers, a plan to gather better information on crash pulses and other crash parameters in actual crashes, utilizing current or augmented crash sensing and recording devices. Two years later, the NTSB issued additional recommendations that NHTSA require EDRs to be installed in school buses and motor coaches. To address these recommendations, NHTSA established an EDR working group of industry, academic, and other government organizations, which met from 1998-2000. In 2001, the working group concluded that EDR technology could have the potential to improve highway safety through improved occupant protection systems; be applied to all types of motor vehicles, but that different types of EDRs would be needed for lightweight vehicles than for heavy trucks and buses; capture a wide range of crash-related data which would be beneficial to researchers, investigators, and manufacturers (if open access, without personal identifiers, was provided); reduce the number and severity of crashes if there is driver and employee awareness of how EDR systems work; be most successful if many vehicles on the road utilize EDRs and there is a corresponding infrastructure to use the data; and be even more effective if integrated with automatic crash notification systems and the car's other electronics (such as global positioning system and cellular phones), thereby providing early notice of and details about a collision. The working group reported that NHTSA was already incorporating EDR data into its motor vehicle research databases. In addition, it pointed out that most EDR systems were unique and proprietary, such that only the vehicle manufacturer was able to download and analyze the data. Based on the research and recommendations of the working group and consumer petitions for using the technology for increasing vehicle safety, NHTSA proposed its first EDR regulation in June 2004 and issued the final regulation in August 2006. The 2006 NHTSA regulation did not mandate vehicles to have EDRs; only those voluntarily equipped are subject to the regulation. (At the time it was estimated that 64% of new light vehicles were already equipped with them.) Rather, in recognizing that this technology was increasingly becoming a feature in many vehicles, NHTSA sought to standardize the types of data being collected so that such data may be put to the most effective future use and to ensure that EDR infrastructure develops in such a way as to speed medical assistance through providing a foundation for automatic crash notification (ACN). Applied to all light vehicles (cars, pick-up trucks, SUVs) with EDRs sold after September 2012, the regulation requires: a standard set of data elements and formatting. The regulation lists 15 technical requirements pertaining to time/interval sample rates. For example, cars equipped with EDRs are required to record crash-related information on vehicle speed, driver safety belt status, and timing of air bag deployment. a few milliseconds of data capture, rather than several minutes. See Appendix A for the specific recording intervals.