August 2016

  1. What are crash avoidance technologies?

    The term "crash avoidance" can encompass a wide variety of vehicle features designed to help the driver operate the vehicle safely. Vehicles increasingly offer advanced technologies that assist the driver with warnings or automatic braking to avoid or mitigate a crash. These advanced technologies vary in their function and how they operate. In general, they monitor driver input and the environment around the vehicle and warn the driver when they detect the possibility of a collision. In some cases, they increase braking power or adjust steering response to make the driver’s input more effective. They also may automatically brake or steer the vehicle if the driver does not take action to avoid the collision. 

  2. What kinds of crash avoidance technologies are currently available for passenger vehicles?

    This list summarizes some of the most common or promising crash avoidance systems. This is not a comprehensive list of technologies, as more are introduced each year. The descriptions are general and may not capture every variation of a given technology.

    Front crash prevention systems use various types of sensors, such as cameras, radar, or light detection and ranging (LIDAR) to detect when the vehicle is getting too close to one in front of it. Most systems issue a warning and precharge the brakes to maximize their effect if the driver brakes. Many systems brake the vehicle autonomously if the driver doesn't respond. In some cases, automatic braking is activated without a preliminary warning. An autobrake system may not always prevent a crash but may reduce vehicle speed, mitigating the severity of the crash.

    Some front crash prevention systems can recognize pedestrians, cyclists and animals. These systems use advanced algorithms coupled with sensors and cameras to spot nonmotorists who are in or about to enter the vehicle's path.

    Some vehicles also are equipped with night vision assist technologies. Night vision assist uses infrared imaging to produce an enhanced view of the road ahead. Some systems provide an audible or visual alert if there is a pedestrian or animal ahead.

    Adaptive cruise control is related to front crash prevention, but it is typically marketed as a convenience, rather than a safety feature. As with regular cruise control, the driver sets the desired speed. The difference is that the forward-mounted sensors track the distance to a lead vehicle, and the engine and brakes are used to maintain a safe gap if traffic slows. As traffic speeds up again, the vehicle accelerates to maintain the preset cruise speed. Some systems allow drivers to adjust the following distance.

    Lane departure warning and lane-keeping support systems use cameras to track the vehicle's position within the lane, alerting the driver if the vehicle is in danger of inadvertently straying across lane markings when the turn signal is not activated. Some systems use haptic warnings, such as steering wheel or seat vibration, while others use audible and/or visual warnings. Some systems cause the vehicle to actively resist moving out of the lane or help direct the vehicle back into the lane through light braking or minor steering adjustments.

    Blind spot detection uses sensors to monitor the side of the vehicle for vehicles approaching blind spots. In many systems, a visual alert appears on or near the side mirrors if a vehicle is detected. An audible alert may activate if the driver signals a turn and there is a vehicle in the blind spot. Some systems also may activate the brake or steering controls to keep the vehicle in its lane.

    Park assist and backover prevention systems help drivers park and back up. Rear object detection systems use cameras and sensors to help the driver look for objects behind the vehicle when backing up. Rearview cameras display what is behind the vehicle. Systems that use radar or ultrasonic sensors, as well as some camera systems, warn the driver if there are objects in the way when the vehicle is in reverse. Some systems automatically apply the brakes to keep the vehicle from backing into or over an object. A cross-traffic alert system detects approaching vehicles that may cross the path of a backing vehicle, warns the driver, and may automatically brake to prevent a collision. Some parking assist systems can automatically parallel park the vehicle.

    • See the backover crashes Q&A for more information on the use of cameras to prevent backover crashes.

    Fatigue warning systems use sophisticated algorithms that monitor driver steering and other behaviors, such as the driver's eye blink rate or blink duration. A system alerts the driver if it detects inattention or drowsiness.

    Curve-adaptive headlights help drivers see better on dark, curved roads. The headlights pivot in the direction of travel based on steering wheel movement and sometimes the vehicle’s speed to illuminate the road ahead.

    Electronic stability control utilizes sensors and a microcomputer to monitor how well a vehicle responds to a driver's steering input. The system selectively applies the brakes and modulates the engine power to keep the vehicle traveling along the path indicated by the steering wheel position.

    Antilock brakes prevent wheels from locking up and skidding during hard braking by monitoring the speed of each wheel and automatically pulsing the brake pressure on any wheels where skidding is detected.

  3. Do crash avoidance features reduce crashes?

    Front crash prevention is reducing crashes. The Institute studied front crash prevention's effectiveness using police-reported crash data from 22 states during 2010-14 and found that vehicles equipped with front crash prevention are much less likely to rear-end other vehicles than the same models without the technology. Cicchino, Jessica B. 2016. Effectiveness of forward collision warning and autonomous emergency braking systems in reducing police-reported crash rates. Arlington, VA: Insurance Institute for Highway Safety. Systems with forward collision warning and automatic braking cut rear-end crashes in half, while forward collision warning alone reduces them by 27 percent. The autobrake systems also greatly reduce rear-end crashes involving injury.

    Volvo's City Safety, designed to help a driver avoid rear-ending another vehicle in slow-moving traffic, was found to reduce rear-end crashes by 43 percent and rear-end crashes with injury by nearly half, compared with similar vehicle models without a standard front crash prevention system. Cicchino, Jessica B. 2016. Effectiveness of forward collision warning and autonomous emergency braking systems in reducing police-reported crash rates. Arlington, VA: Insurance Institute for Highway Safety.  

    The Highway Loss Data Institute (HLDI) conducted similar studies comparing insurance claim rates for vehicles equipped with front crash prevention with claim rates for the same models without the technology. In total, HLDI has studied 12 front crash prevention systems from seven manufacturers. Vehicles equipped with these systems consistently show lower rates of claims for damage to other vehicles and for injuries to people in other vehicles. Highway Loss Data Institute. 2012. Mercedes-Benz collision avoidance features: initial results. HLDI Bulletin 29(7). Highway Loss Data Institute. 2013. Acura collision avoidance features: an update. HLDI Bulletin 30(15). Highway Loss Data Institute. 2012. Volvo collision avoidance features: initial results. HLDI Bulletin 29(5). Highway Loss Data Institute. 2016. Mazda collision avoidance features: an update. HLDI Bulletin 33(3). Highway Loss Data Institute. 2015. 2013-2015 Honda Accord collision avoidance features. HLDI Bulletin, 32(33). Highway Loss Data Institute. 2016. 2013-15 Subaru collision avoidance features. HLDI Bulletin, 33(6). Highway Loss Data Institute. 2015. Volvo City Safety loss experience – a long-term update. HLDI Bulletin, 32(1). Highway Loss Data Institute. 2016. Fiat Chrysler collision avoidance features: initial results. HLDI Bulletin, 33(2). These studies include all crash configurations, so the effects appear more modest than the effects in studies focusing on rear-end crashes. Claim rates for damage to other vehicles are 10-16 percent lower for vehicles equipped with a warning system and autobrake, and 7-22 percent lower for vehicles equipped with a warning system only. Among low-speed systems, Volvo's City Safety reduces rates of claims for damage to other vehicles 15 percent, compared with similar vehicle models without a standard front crash prevention system, Highway Loss Data Institute. 2015. Volvo City Safety loss experience – a long-term update. HLDI Bulletin, 32(1). and Mazda's Smart City Brake support reduces claims for damage to other vehicles by 11 percent. Highway Loss Data Institute. 2016. Mazda collision avoidance features: an update. HLDI Bulletin 33(3). Front crash prevention systems also reduce rates of claims for injuries to occupants of other vehicles by 4-32 percent.

    The real-world effectiveness of other crash avoidance technologies is less clear. HLDI examined the effectiveness of lane departure warning systems from six manufacturers and did not find any consistent changes in rates of insurance claims covering damage to at-fault vehicles, which is the type of claim that would likely follow a single-vehicle run-off-road crash, for vehicles with lane departure warning compared with the same vehicle models without the system. Highway Loss Data Institute. 2012. Mercedes-Benz collision avoidance features: initial results. HLDI Bulletin 29(7). Highway Loss Data Institute. 2012. Volvo collision avoidance features: initial results. HLDI Bulletin 29(5). Highway Loss Data Institute. 2016. Mazda collision avoidance features: an update. HLDI Bulletin 33(3). Highway Loss Data Institute. 2015. 2013-2015 Honda Accord collision avoidance features. HLDI Bulletin, 32(33). Highway Loss Data Institute. 2016. 2013-15 Subaru collision avoidance features. HLDI Bulletin, 33(6). Highway Loss Data Institute. 2011. Buick collision avoidance features: initial results. HLDI Bulletin 28(22).

    Blind spot monitoring and rear cameras have shown more promise in HLDI's research, although results are not yet conclusive. HLDI has examined blind spot monitoring systems from seven manufacturers. Highway Loss Data Institute. 2012. Mercedes-Benz collision avoidance features: initial results. HLDI Bulletin 29(7). Highway Loss Data Institute. 2013. Acura collision avoidance features: an update. HLDI Bulletin 30(15). Highway Loss Data Institute. 2012. Volvo collision avoidance features: initial results. HLDI Bulletin 29(5). Highway Loss Data Institute. 2016. Mazda collision avoidance features: an update. HLDI Bulletin 33(3). Highway Loss Data Institute. 2016. 2013-15 Subaru collision avoidance features. HLDI Bulletin, 33(6). Highway Loss Data Institute. 2016. Fiat Chrysler collision avoidance features: initial results. HLDI Bulletin, 33(2). Highway Loss Data Institute. 2011. Buick collision avoidance features: initial results. HLDI Bulletin 28(22). Five systems have reduced rates of claims for damage to other vehicles. The four rear-camera systems examined by HLDI have reduced rates of damage to other vehicles, with two systems reducing these rates significantly by 4-6 percent; however, Honda Pilot vehicles with a rear camera have significantly higher rates of claims covering damage to at-fault vehicles than those without a rear camera. Highway Loss Data Institute. 2012. Mercedes-Benz collision avoidance features: initial results. HLDI Bulletin 29(7). Highway Loss Data Institute. 2016. Mazda collision avoidance features: an update. HLDI Bulletin 33(3). Highway Loss Data Institute. 2016. 2013-15 Subaru collision avoidance features. HLDI Bulletin, 33(6). Highway Loss Data Institute. 2015. Honda Pilot rear view camera: initial results. HLDI Bulletin 32(9).
    The Buick Lucerne's rear parking sensors have resulted in large reductions in damage claim rates, while the Mercedes-Benz parking sensor system has not. Highway Loss Data Institute. 2012. Mercedes-Benz collision avoidance features: initial results. HLDI Bulletin 29(7). Highway Loss Data Institute. 2011. Buick collision avoidance features: initial results. HLDI Bulletin 28(22).

  4. If a crash avoidance system doesn't prevent a crash, can it still be beneficial?

    Yes. Even if a front crash prevention system doesn't avoid a crash altogether, it may still reduce the impact speed, thereby making a crash less severe. To show why reducing speed is important, IIHS conducted two demonstration crash tests at different speeds. In each test, a 2013 Mercedes-Benz C-Class ran into the back of a stationary 2012 Chevrolet Malibu. The tests illustrate what happens in a 25 mph crash when the striking vehicle doesn't have autobrake, compared with what happens when the speed is reduced by 13 mph, the amount by which the C-Class's autobrake system reduced the impact speed in IIHS track testing. Damage in the higher speed crash test was about $28,000. The Malibu was a complete loss. Lowering the speed to 12 mph trimmed the damage to $5,700. Insurance Institute for Highway Safety. 2013. Crash tests show how autobrake can mitigate crash severity, damage costs. Status Report 48(7):5. A similar speed reduction in a higher speed crash could significantly reduce injury risk, as well as vehicle damage. Krafft, M.; Kullgren, A.; Lie., A.; Strandroth, J.; & Tingvall, C. 2009. The effects of automatic emergency braking on fatal and serious injuries. Proceedings of the 21st International Technical Conference on the Enhanced Safety of Vehicles.

  5. What resources are available for consumers who want to purchase a vehicle with crash avoidance features?

    Advanced crash avoidance features started out as options on a few luxury vehicles and have steadily spread to more of the fleet, including many nonluxury models. Front crash prevention is likely to become even more prevalent. In March 2016, the National Highway Traffic Safety Administration (NHTSA) and IIHS announced a commitment of 20 major automakers, representing 99 percent of U.S. light vehicle sales, to make front crash prevention systems standard on virtually all models by September 2022.

    Information by make and model on the availability of forward collision warning, autobrake, lane departure warning, lane departure prevention, adaptive headlights and blind spot detection can be found here.

    An Institute test program rates the performance of front crash prevention systems to help consumers compare them and to encourage automakers to speed adoption of the technology. The Institute rates models with optional or standard front crash prevention systems as superior, advanced or basic, depending on whether they offer autobrake and, if so, how effective it is in tests at 12 and 25 mph.

    Since research indicates that systems with autobrake reduce crashes to a greater extent than similar systems with forward collision warning only, Cicchino, Jessica B. 2016. Effectiveness of forward collision warning and autonomous emergency braking systems in reducing police-reported crash rates. Arlington, VA: Insurance Institute for Highway Safety. vehicles must brake automatically to get the top ratings. To earn a basic rating, vehicles must have a forward collision warning system that meets performance criteria specified by NHTSA. For an advanced rating, vehicles must have forward collision warning and avoid a crash or reduce speed by at least 5 mph in one of the tests. Vehicles earning the top rating of superior must avoid a crash or substantially reduce speeds in both tests. Information on IIHS ratings can be found here.

    In addition to forward collision warning, NHTSA has recognized the potential importance of lane departure warning systems and rear-view video systems for backover prevention by incorporating them into its New Car Assessment Program. Vehicles are credited with having these systems if their system can pass performance specifications.

  6. How do drivers respond to new crash avoidance features?

    Appropriate driver responses and acceptance of crash avoidance technologies are critical to their success. If drivers find the systems annoying or not useful, they may disable them. Similarly, if drivers experience warnings but don't understand them, don't trust them, are overwhelmed by them, or don't take an appropriate corrective action, then the systems will be ineffective.

    Early research using simulators has shown collision warning systems can redirect the driver’s attention to the road and improve reaction time, but little is known about how drivers respond in real-world driving. Lee, J.D.; McGehee, D.V.; Brown, T.L.; and Reyes, M.L. 2002. Collision warning timing, driver distraction, and driver response to imminent rear-end collisions in a high-fidelity driving simulator human factors. Human Factors 44(2): 314-34.

    Institute surveys of owners of luxury and nonluxury vehicles with crash avoidance technologies found that, despite some annoyance about false alerts, for example, most drivers left the systems turned on most of the time, felt the systems made them safer drivers and would want them in their next vehicle. Braitman, K.A.; McCartt, A.T.; Zuby, D.S.; and Singer, J. 2010. Volvo and Infiniti drivers' experiences with select crash avoidance technologies. Traffic Injury Prevention 11(3):270-8. Eichelberger, A.H. and McCartt, A.T. 2014. Volvo drivers' experiences with advanced crash avoidance and related technologies. Traffic Injury Prevention 15(2):187-95. Cicchino, J.B. and McCartt, A.T. 2015. Experiences of model year 2011 Dodge and Jeep owners with collision avoidance and related technologies. Traffic Injury Prevention 16(3):298-303. Eichelberger, A.H. and McCartt, A.T. 2016. Toyota drivers' experiences with Dynamic Radar Cruise Control, Pre-Collision System, and Lane-Keeping Assist. Journal of Safety Research 56:67-73. Observations at Honda dealers in 2015 found that forward collision warning was activated in all but one of 184 vehicles that arrived for service. Reagan, Ian J.; McCartt, Anne T. 2016. Observed activation status of lane departure warning and forward collision warning of Honda vehicles at dealership service centers. Arlington, VA: Insurance Institute for Highway Safety. Activation of lane departure warning was much lower, at 33 percent.

    One concern is that drivers might rely on crash avoidance systems too much and feel freer to look away from the road or take other risks. In the Institute's surveys of owners of vehicles with various technologies, many owners reported safer driving habits with the systems (e.g., following less closely with adaptive cruise control, using turn signals more often with lane departure warning). Fewer owners reported potentially unsafe behavior, such as waiting for an alert before braking or allowing the vehicle to brake for them at least some of the time.

  7. What are some of the limitations of crash avoidance technologies?

    For systems requiring drivers to take action, their effectiveness depends on whether drivers use the technologies, understand the information from the system and respond appropriately. Interpreting warnings from multiple systems may be confusing or even distracting for some drivers.

    In addition to driver challenges, the technology itself can have limitations. For example, lane departure warning systems use sensors to register lane markings or the road edge, which may be problematic on roads that aren't well marked or are covered with snow. Sensors such as cameras, radar and LIDAR also may not function well in low light or inclement weather. Some systems only work at certain speeds. Other systems don't operate until turned on by the driver.

  8. What new technologies can we expect in the future?

    The landscape of in-vehicle technologies is rapidly changing as new features continue to be introduced. Advances also are being made in intelligent transportation systems that allow vehicles to communicate with one another or with the roadway infrastructure.

    Vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) communications, collectively known as connected vehicle technology, are prototype safety systems in which vehicles and roadway infrastructure communicate over a wireless network.

    With V2V communication, vehicles transmit information regarding their actions to other vehicles. For example, in a long chain of vehicles, if the lead vehicle suddenly brakes, this information will be transmitted to every other vehicle in the chain so that the other drivers are alerted. It also could be possible for the trailing vehicles to automatically begin braking when the lead vehicle's signal is received.

    With V2I communication, cars receive and transmit information to roadway infrastructure. For example, highway systems could monitor vehicle location within a lane. If the vehicle is detected drifting out of a lane, the system could alert the vehicle. In urban environments, traffic signals can alert vehicles of an impending light change so drivers can prepare to stop.

    A 2013 pilot study in Ann Arbor, Mich., tested the functionality and reliability of these connected vehicle technologies. Research and Innovative Technology Administration. 2012. Connected vehicle research. Available at http://www.its.dot.gov/connected_vehicle/connected_vehicle.htm. Accessed: June 20, 2012. The results indicate connected vehicle technologies are technically feasible and would reduce property-damage and injury crashes. However, there are some barriers to wide adoption, including issues privacy and security concerns, as well as technical aspects and performance requirements of the systems. Harding, J.; Powell, G.; Yoon, R.; Fikentscher, J.; Doyle, C.; Sade, D.; Lukuc, M.; Simons, J.; and Wang, J. 2014. Vehicle-to-vehicle communications: readiness of V2V technology for application. Report no. DOT HS-812-014. Washington, DC: National Highway Traffic Safety Administration. NHTSA is taking steps to work through privacy and security issues and enable this technology in vehicles. The agency has solicited feedback from the public ahead of issuing a proposed rule. Office of the Federal Register. 2014. National Highway Traffic Safety Administration – Advanced notice of proposed rulemaking. Docket no. NHTSA-2014-0022; 49 CFR Part 571 Federal Motor Vehicle Safety Standards: Vehicle-to-Vehicle (V2V) Communications. Washington, DC: National Archives and Records Administration.  In addition, the U.S. Department of Transportation is funding additional pilot deployment sites to refine system and operational requirements and inform a comprehensive deployment plan. United States Department of Transportation. Connected vehicles CV Pilot Deployment Program. Available at: http://www.its.dot.gov/pilots/index.htm. Accessed February 26, 2016.

  9. What is an autonomous vehicle and will it soon be driving me?

    An autonomous vehicle is equipped with technology that can sense the environment around it and drive itself without active physical control or monitoring by a human driver. Vehicles with crash avoidance systems such as front crash prevention may have some automated functions but are not defined as fully autonomous by the federal government unless the vehicle can perform all safety-critical driving functions and monitor roadway conditions for an entire trip without any driver input. National Highway Traffic Safety Administration. 2013. Preliminary statement of policy concerning automated vehicles. Washington, DC: U.S. Department of Transportation. Available: http://www.nhtsa.gov/Research/Crash+Avoidance/Automated+Vehicles. Accessed: February 26, 2016.

    Although no current vehicle is fully autonomous, vehicles already exist that can operate autonomously in some driving situations. The best-known example is Google’s driverless car, which was conceived in 2005. Major auto manufacturers are also working on prototypes, many of which are being tested on-road.

    NHTSA is monitoring these developments and conducting its own research to determine whether additional vehicle safety standards are needed for autonomous vehicles and what those standards need to cover. National Highway Traffic Safety Administration. 2015. April 1, 2015, letter to California DMV regarding vehicle automation. Washington, DC: U.S. Department of Transportation. Available: http://www.nhtsa.gov/Research/Crash+Avoidance/Automated+Vehicles. Accessed: February 26, 2016.

    Regulating the use of driverless cars on U.S. roads will be challenging. In 2011, Nevada enacted a law that permits testing on public roads, and California, Florida, Michigan, and the District of Columbia also now permit testing. In these jurisdictions, testing requires a human operator to be behind the steering wheel in case a manual intervention is required.

    California is drafting regulations that would allow the public to operate autonomous vehicles on public roads. The current draft rules would allow a manufacturer to lease a driverless car meeting certain requirements to a licensed driver for a carefully monitored, three-year deployment period, but would require the human operator to be behind the steering wheel at all times.

March 2016

  1. Do all headlights sold today provide enough light?

    No. Although data about the on-road performance of headlights is limited, IIHS ratings show that visibility provided by headlights varies widely. The Institute released its first headlight ratings in 2016. Out of more than 80 headlight systems available on 31 midsize cars that were evaluated, only one system received a good rating. More than half were rated poor because of inadequate visibility, excessive glare from low beams for oncoming drivers, or both.

    It takes 1.5 seconds for a driver to react to an unexpected event under ideal conditions. Green, M. 2000. "How long does it take to stop?" Methodological analysis of driver perception-brake times. Transp.Human Factors 2(3): 195-216. At a speed of 55 mph, a car travels about 120 feet during this brief period. Once the driver applies the brakes, it takes more than 144 feet, on average, to stop at this speed. Jernigan, J.D. and Kodaman, M.F. 2001. An investigation of the utility and accuracy of the table of speed and stopping distances specified in the Code of Virginia. Final Report. Report no. VTRC 01-R13. Charlottesville, VA: Virginia Transportation Research Council. Given these distances, 42 percent of the low-beam headlight systems the Institute tested don't provide enough light for a driver going 55 mph on a straight road to stop in time after spotting an obstacle in his or her lane. It's important to note that low beams provide even less illumination on the left side of a straight road and when driving on a curve.

  2. Does the U.S. government regulate headlights?

    There are federal regulations on headlights, but headlights that meet the regulations don't necessarily have similar on-road performance. Under the standard, a headlamp is placed on a test rig, and light intensity is measured at different angles relative to the center of the lamp. Measurements are taken for visibility and glare, but the standard permits a large range of intensities and the angles can be adjusted within a relatively large tolerance. In addition, once the headlights are put on a vehicle, the regulations allow a wide range of mounting heights and widths and don't say how they should be aimed. As a result, two vehicles could be equipped with the same headlights but have a large difference in the distances illuminated.

    One clear requirement is the need for all vehicles to have separate low-beam and high-beam headlights. The requirement is intended to provide maximum visibility with high-beam headlights when drivers are on unlit roads without other traffic around and to provide sufficient low-beam visibility while limiting glare exposure when oncoming or leading vehicles are near.

  3. What technological innovations have been made in vehicle lighting?

    Between 1940 and the mid-1980s, almost every vehicle in the United States was sold with standardized sealed-beam glass headlamps. Moore, D.W. 1998. Headlamp history and harmonization. Report no. UMTRI-98-21. Ann Arbor, MI: University of Michigan Transportation Research Institute. Beginning in the 1970s, these were filled with halogen gas to improve performance. Since the mid-1980s, most vehicle models have had customized headlights with replaceable bulbs. Halogen bulbs now have competition from LED and high-intensity discharge (HID) lamps. These newer light sources are more efficient than halogen bulbs (and LEDs are much more efficient than HIDs), so they can produce more light with the same amount of energy. They also produce light with a more natural color than halogen bulbs.

    Many of today's vehicles are available with curve-adaptive headlights. These headlights pivot in the direction of travel based on steering wheel movement and sometimes the vehicle's speed to illuminate the road ahead. They are intended to make it easier to see on dark, curved roads.

    Another increasingly common feature is high beam assist. This technology uses a camera to automatically switch between high beams and low beams, depending on whether other vehicles are present. The driver still has the option to manually switch between low and high beams.

    Headlights with an adaptive driving beam, not to be confused with curve-adaptive headlights, are similar to high beam assist. However, instead of switching the high beams on and off, they continuously adjust the high-beam pattern to create a shadow around other vehicles. In this way, adaptive driving beams offer high-beam visibility except for the segment of the beam that is blocked out to limit glare for oncoming or lead drivers.

    Adaptive driving beams are currently prohibited in the United States because the regulations require separate high- and low-beam systems. The Society of Automotive Engineers plans to publish recommendations for test procedures, performance requirements, and design and installation guidelines for adaptive driving beams to facilitate the revision of federal safety standards to allow this technology.

  4. Do these innovations improve safety?

    Studies show that curve-adaptive headlights reduce crashes, though it can be hard to tease out how much of the benefit is from HID or LED lamps and how much is from curve adaptivity.

    HLDI studied curve-adaptive headlights offered by Acura, Mazda, Mercedes and Volvo and found that claim rates generally fell. Highway Loss Data Institute. 2013. Acura collision avoidance features – an update. HLDI Bulletin 30(15). Highway Loss Data Institute. 2015. Mazda collision avoidance features. HLDI Bulletin 32(22). Highway Loss Data Institute. 2012. Mercedes-Benz collision avoidance features: initial results. HLDI Bulletin 29(7). Highway Loss Data Institute. 2012. Volvo collision avoidance features: initial results. HLDI Bulletin 29(5). The effect was particularly consistent for claims under property damage liability coverage, which pays for damage to other vehicles and property, where rates fell as much as 9 percent.

    The reduction of property damage liability claim rates was surprising, since only about 13 percent of police-reported crashes occur on dark roads and involve more than one vehicle. An even smaller percentage are multiple-vehicle, nighttime crashes occurring on a curve, where curve-adaptive headlights would be expected to have the most effect. It's possible that other differences between the curve-adaptive headlights and conventional ones besides steerability may have played a role in reducing crashes with other vehicles. Curve-adaptive headlights usually have LED or HID lamps, while fixed lights can be LED, HID or halogen.

    In an experimental study with volunteers driving a vehicle with three different lighting systems, curve-adaptive high-intensity discharge (HID) headlights allowed drivers to spot a hard-to-see object on a dark, curvy road about one-third second earlier than with conventional fixed headlights. Reagan, I.J.; Brumbelow, M.L.; and Frischmann, T. 2015. On-road experiment to assess drivers' detection of roadside targets as a function of headlight system, target placement, and target reflectance. Accident Analysis and Prevention 76:74-82.

    High beam assist is not yet widespread enough to determine if it reduces crashes, but researchers from IIHS and the University of Michigan Transportation Research Institute found that drivers in and around Ann Arbor, Mich., didn't use their high beams enough. Reagan, I.J.; Brumbelow, M.J.; and Flannagan, M.J. 2016. The effects of rurality, proximity to other traffic, and roadway curvature on high beam headlamp use rates. Arlington, VA: Insurance Institute for Highway Safety. Only 18 percent of drivers who were isolated enough to make use of their high beams did so. High beam assist could improve this rate if drivers are simply forgetting to turn on their high beams, are unsure whether oncoming vehicles are far enough away to do so safely, or understate the effects of high beams on safety.

  5. Don't headlights that provide more light cause glare for drivers of other vehicles?

    Not necessarily. Properly aimed headlights can illuminate the road ahead without getting in other drivers' eyes. Many people encounter blue-colored headlights that cause disturbing glare, but these often are the result of illegal aftermarket HID conversion kits. Specialty Equipment Market Association. 2007. Government clamps down on HID conversion kits. SEMA eNews 10(18). Diamond Bar, CA.

  6. Where can I get information about headlight performance?

    IIHS began publishing headlight ratings in 2016, beginning with midsize luxury and nonluxury cars. Several different headlight combinations may be available on a single model, and the Institute tries to test all of them, as they become available from dealers.

    Each rating provides information on the amount of visibility provided by low beams and high beams as a vehicle travels straight and on curves, and whether the glare produced for other drivers is excessive. Credit is also given for vehicles that have high beam assist.

  7. What are daytime running lights, and what safety benefits do they provide?

    Daytime running lights (DRLs) are low-intensity headlights that are lit whenever a vehicle is running. A low-cost method to reduce crashes, they are especially effective in preventing daytime head-on and front-corner collisions by making it easier for vehicles to be seen, particularly as they approach from far away or in inclement weather.

    Laws in Canada and many European countries require cars, trucks and buses to operate with lights on during the daytime. These requirements began in 1989 for Canada and in 2011 for the European Union. No U.S. state mandates DRLs, but some require drivers to operate vehicles with lights on in bad weather.

    In the U.S., DRLs were first offered on a handful of 1995 passenger vehicles. Since then, they have become quite common. DRLs are standard on all General Motors, Honda, Subaru, Volkswagen and Volvo models. Other manufacturers also offer daytime running lights on certain models. Retrofit kits can be purchased for vehicles that didn't come with DRLs.

  8. How effective are DRLs?

    Nearly all published reports indicate DRLs reduce multiple-vehicle daytime crashes. A 1985 Institute study determined that commercial fleet passenger vehicles modified to operate with DRLs were involved in 7 percent fewer daytime multiple-vehicle crashes than similar vehicles without DRLs. Stein, H. 1985. Fleet experience with daytime running lights in the United States. SAE Technical Paper Series 851239. Warrendale, PA: Society of Automotive Engineers. Multiple-vehicle daytime crashes account for about half of all police-reported crashes in the United States. A 2002 Institute study reported a 3 percent decline in multiple-vehicle daytime crash risk in nine U.S. states concurrent with the introduction of DRLs. Farmer, C.M. and Williams, A.F. 2002. Effects of daytime running lights on multiple-vehicle daylight crashes in the United States. Accident Analysis and Prevention 34(2):197-203.

    Federal researchers, using data collected nationwide from 1995 to 2001, concluded that there was a 5 percent decline in daytime, two-vehicle, opposite-direction crashes. Tessmer, J.M. 2004. An assessment of the crash-reducing effectiveness of passenger vehicle daytime running lamps (DRLs). Report no. DOT HS-809-760. Washington, DC: National Highway Traffic Safety Administration. However, a 2008 federal study concluded that DRLs reduce crash involvements of pickups, SUVs and vans but have no significant effect on crashes of passenger cars. Wang, J.S. 2008. The effectiveness of daytime running lights for passenger vehicles. Report no. DOT HS-811-029. Washington, DC: National Highway Traffic Safety Administration.

March 2016

  1. What is electronic stability control (ESC)?

    ESC is a vehicle control system comprised of sensors and a microcomputer that continuously monitors how well a vehicle responds to a driver's steering input, selectively applies the vehicle brakes, and modulates engine power to keep the vehicle traveling along the path indicated by the steering wheel position. This technology helps prevent the sideways skidding and loss of control that can lead to rollovers. It can help drivers maintain control during emergency maneuvers when their vehicles otherwise might spin out, or reduce vehicle speed to prevent running off the outside of a curve. The systems have been marketed under various names, including dynamic stability control, vehicle stability control and dynamic stability and traction control, among others.

  2. How does ESC help drivers maintain control?

    A driver loses control when the vehicle goes in a direction different from the one the steering wheel position indicates. This typically occurs when a driver tries to turn very hard or turn on a slippery road. Then the vehicle may understeer or oversteer. When it oversteers it turns more than the driver intended because the rear end is spinning or sliding out. When a vehicle understeers it turns less than the driver intended and continues in a forward direction because the front wheels have insufficient traction. ESC can prevent under- and oversteer by selectively braking wheels to produce a counteracting force which helps correct the vehicle's direction of travel. In some cases engine throttle also is reduced.

    How ESC works
  3. How effective is ESC in preventing crashes?

    In Institute studies, ESC has been found to reduce fatal single-vehicle crash risk by 49 percent and fatal multiple-vehicle crash risk by 20 percent for cars and SUVs. Many single-vehicle crashes involve rolling over, and ESC effectiveness in preventing rollovers is even more dramatic. It reduces the risk of fatal single-vehicle rollovers by 75 percent for SUVs and by 72 percent for cars. Farmer, C.M. 2010. Effects of electronic stability control on fatal crash risk. Arlington, VA: Insurance Institute for Highway Safety. Federal studies also show large benefits. The National Highway Traffic Safety Administration (NHTSA) estimates the installation of ESC reduces single-vehicle crashes of cars by 32 percent and single-vehicle crashes of SUVs by 57 percent. NHTSA estimates that ESC has the potential to prevent 72 percent of the car rollovers and 64 percent of the SUV rollovers that would otherwise occur in single-vehicle crashes. Sivinski, R. 2011. Crash prevention effectiveness of light-vehicle electronic stability control: an update of the 2007 NHTSA evaluation. Report no. DOT HS-811-486. Washington, DC: U.S. Department of Transportation.  

    ESC also has great potential to prevent rollover crashes of large trucks. NHTSA estimates that ESC on large trucks could prevent 40 to 56 percent of rollovers and 14 percent of loss-of-control crashes. Wang, J.S. 2011. Effectiveness of stability control systems for truck tractors. Report no. DOT HS-811-437. Washington, DC: Department of Transportation.

  4. Does ESC activate in typical everyday driving?

    For most drivers ESC isn't likely to activate frequently. It won't prevent most of the fender-bender crashes that occur so often in stop-and-go traffic, for example. It's designed to help a driver in the relatively rare event of loss of control at high speed or on a slippery road.

  5. Does the government require ESC?

    As of the 2012 model year, the federal government requires ESC in all cars, SUVs, pickups and minivans. Office of the Federal Register. 2007. National Highway Traffic Safety Administration – Final rule. Docket no. NHTSA-2007-27662; 49 CFR Parts 571 and 585 – Federal Motor Vehicle Safety Standards, Electronic stability control systems, Controls and displays. Federal Register, vol. 72, no. 66, pp. 17236-322. Washington, DC: National Archives and Records Administration. A similar requirement for truck tractors was finalized in 2015. Office of the Federal Register. 2015. National Highway Traffic Safety Administration – Final rule. Docket no. NHTSA-2015-0056; 49 CFR Part 571 – Federal Motor Vehicle Safety Standards, Electronic stability control systems for heavy vehicles. Federal Register, vol. 80, no. 120, pp. 36049-36110. Washington, DC: National Archives and Records Administration. Most new truck tractors will be required to have ESC as of Aug. 1, 2017. The remaining types have until 2019.

  6. How long has ESC been available?

    ESC was introduced in 1995 as optional equipment on luxury cars. By the 2001 model year it was standard on a number of high-selling vehicles and available as an option on many more.

    NHTSA phased in its ESC rule, requiring the technology on 55 percent of model year 2009 vehicles and increasing the percentage each year until model year 2012, when manufacturers had to equip all their passenger vehicles with ESC. Office of the Federal Register. 2007. National Highway Traffic Safety Administration – Final rule. Docket no. NHTSA-2007-27662; 49 CFR Parts 571 and 585 – Federal Motor Vehicle Safety Standards, Electronic stability control systems, Controls and displays. Federal Register, vol. 72, no. 66, pp. 17236-322. Washington, DC: National Archives and Records Administration. Prior to 2012, the Institute required vehicles to have ESC in order to qualify for a TOP SAFETY PICK award.

  7. Can ESC help reduce insurance losses?

    Yes. Losses under collision coverage are about 15 percent lower for vehicles with ESC than for predecessor models without it, according to an analysis by HLDI. Highway Loss Data Institute. 2006. Electronic stability control. HLDI Bulletin 23(1). Arlington, VA. ESC doesn't have much effect on liability claims filed when an at-fault driver damages someone else's car or property or the frequency of personal injury claims filed to cover medical expenses.

February 2016

  1. What are antilock brakes?

    Antilock brakes are designed to help drivers avoid crashes. Without antilocks, hard braking can cause wheels to lock, sending a vehicle into a skid. Wheel lockup can result in longer stopping distances, loss of steering control and, when road friction is uneven, loss of stability if the vehicle begins to spin.

    The main benefit of an antilock braking system (ABS) is that it can reduce these problems on wet and slippery roads. ABS works with a vehicle's normal service brakes to decrease stopping distance and increase the control and stability of the vehicle during hard braking.

    The principle behind ABS is that a skidding wheel provides less stopping force and control than a wheel that is rotating. Antilocks prevent wheels from skidding by monitoring the speed of each wheel and automatically pulsing the brake pressure on any wheels where skidding is detected. ABS doesn’t make much difference in stopping distances on dry roads, although it can enhance vehicle stability and allow the driver to maintain steering control during an emergency stop, when conventional brakes might allow wheel lockup and skidding.

  2. How does ABS work?

    ABS differs among vehicles, but there are some basic similarities. Each system has sensors that monitor the rotational speeds of selected wheels when brakes are applied. When one of these wheels approaches lockup, a control unit reduces brake pressure to that wheel or set of wheels just enough to allow rotation again. This typically happens many times per second, resulting in improved control and, on many wet and slippery surfaces, shorter stopping distances.

    Most passenger vehicles have four-wheel systems with wheel-speed sensors on each wheel. In one type of system, ABS reduces brake pressure to both rear wheels whenever one approaches lockup. Brake pressure to the front wheels of four-wheel systems is controlled independently to maximize stopping power, which is concentrated in the front. In four-wheel independent systems, each wheel is controlled individually, so when any one approaches lockup, brake pressure is reduced to that wheel.

    Some pickups and cargo vans have rear-wheel-only antilock systems to address different braking needs when vehicles are loaded versus unloaded. ABS monitors the rotational speeds of rear wheels only and releases pressure to both when either is about to lock.

    Tractor-trailers have separate antilock systems for the tractors and the trailers. Ideally, both the tractor and trailer of a combination rig should have antilock brakes, but putting antilocks on either component should produce improvement compared with conventional brakes. With antilocks on the tractor only, a driver can maintain better steering control even if trailer wheels lock and the trailer swings. If only the trailer has ABS, trailer swing can be reduced even if steering control is lost.

    ABS is particularly important on motorcycles because locking a wheel during hard braking, especially the front wheel, often results in a serious fall. Motorcycle ABS systems operate on both front and rear wheels. They typically involve separate controls for each wheel, although ABS may be included in systems that link the operation of both brakes.

  3. Why doesn't ABS reduce stopping distances as much on dry roads as wet ones?

    Adequate braking is easy to achieve on dry roads with or without antilock brakes. Even if wheels lock, the coefficient of friction between tires and road surface still is relatively high, so a vehicle stops relatively quickly.

  4. Has ABS on passenger vehicles reduced crashes?

    Although antilocks perform well on the test track, there is little evidence that they have substantially reduced real-world crashes. A 1994 Highway Loss Data Institute (HLDI) study Highway Loss Data Institute. 1994. Collision and property damage liability losses of passenger cars with and without antilock brakes. Insurance special report A-41. Arlington, VA. and a subsequent 1995 study Highway Loss Data Institute. 1995. Three years' on-the-road experience with antilock brakes: an update. Insurance special report A-47. Arlington, VA. compared insurance claims for groups of otherwise identical cars with and without antilocks, finding no differences in the frequency or cost of crashes for which insurance claims for vehicle damage were filed. Because ABS should make the most difference on wet and slippery roads, researchers also studied the insurance claims experience in 29 states during winter months. Even here they found no difference in claim frequency for vehicles with and without antilock brakes. A 1997 Institute study Farmer, C.M.; Lund, A.K.; Trempel, R.E.; and Braver, E.R. 1997. Fatal crashes of passenger vehicles before and after adding antilock braking systems. Accident Analysis and Prevention 29(6):745-57. and a 2001 update Farmer, C.M. 2001. New evidence concerning fatal crashes of passenger vehicles before and after adding antilock braking systems. Accident Analysis and Prevention 33(3):361-9. reported no difference in the overall fatal crash involvement of cars with and without antilocks.

    According to one federal report, "the overall, net effect of antilock brakes" on both police-reported crashes and fatal crashes "was close to zero." Kahane, C.J. 1994. Preliminary evaluation of the effectiveness of antilock brake systems for passenger cars. Report no. DOT HS-808-206. Washington, DC: National Highway Traffic Safety Administration. A more recent federal report concluded that ABS reduces overall crash involvement risk by 6 percent for cars and 8 percent for pickups and SUVs but has no effect on fatal crash risk. Kahane, C.J. and Dang, J.N. 2009. The long-term effect of ABS for passenger cars and LTVs. Report no. DOT HS-811-182. Washington, DC: National Highway Traffic Safety Administration. Other researchers have found that antilock-equipped cars are less likely to rear-end other vehicles but more likely to have other vehicles rear-end them. Evans, L. and Gerrish, P. 1996. Antilock brakes and risk of front and rear impact in two-vehicle crashes. Accident Analysis and Prevention 28(3):315-23. The net result is little effect on overall crash risk. Still another analysis found a net benefit of antilocks on nonfatal crashes but no effect on fatal crashes. Padmanaban, J. and Lau, E. 1996. Accident experience of passenger vehicles with four-wheel antilock braking systems. Proceedings of the 40th Annual Conference of the Association for the Advancement of Automotive Medicine, 111-25. Des Plaines, IL: Association for the Advancement of Automotive Medicine.

  5. Why hasn't passenger vehicle ABS reduced crashes as expected?

    No one knows for sure why ABS test performance has not translated into a substantial reduction in real-world crashes. A possible reason is that the average motorist rarely experiences total loss of vehicle control, which antilocks are designed to prevent. There also is evidence that many drivers in the early days of antilock brakes did not know how to use them effectively. A 1994 Institute survey of drivers with antilock-equipped cars found that more than 50 percent in North Carolina and 40 percent in Wisconsin incorrectly thought they should pump the brakes. Williams, A.F. and Wells, J.K. 1994. Driver experience with antilock brake systems. Accident Analysis and Prevention 26(6):807-11.

  6. Is motorcycle ABS effective at reducing crashes?

    Yes. Results from recent studies by IIHS and HLDI compared crash rates for motorcycles equipped with optional ABS against the same models without the option. The rate of fatal crashes per 10,000 registered vehicle years was 31 percent lower for motorcycles equipped with optional ABS than for those same motorcycles without ABS. Teoh, E.R. 2013. Effects of antilock braking systems on motorcycle fatal crash rates: an update. Insurance Institute for Highway Safety. Arlington, VA.  In crashes of all severities, the frequency at which insurance collision claims were filed was 20 percent lower for the ABS models. Highway Loss Data Institute. 2013. Evaluation of motorcycle antilock braking systems alone and in conjunction with combined control braking systems. HLDI Bulletin 30(10). Based on these findings, IIHS and HLDI have petitioned the National Highway Traffic Safety Administration to require manufacturers to equip all new motorcycles with this technology.

  7. How long have antilock brakes been around? Are they widely available?

    The idea of antilock brakes has been around for years. They first were used on airplanes in the 1950s. A rear-wheel system was developed for the 1969 Ford Thunderbird, and the 1971 Chrysler Imperial had four-wheel antilocks.

    Modern antilocks were first introduced on 1985 models. By the 1987 model year, they were standard or optional on about 30 domestic and foreign car models. Availability soared to 90 models the next year.

    ABS is a component of electronic stability control (ESC). Thus, the federal requirement for ESC has made antilock brakes standard equipment on all passenger vehicles as of the 2012 model year.

  8. Is ABS required on big truck rigs?

    In March 1995, the National Highway Traffic Safety Administration issued a rule requiring antilock brakes for heavy trucks, tractors, trailers and buses. All new truck tractors were required to have antilocks after March 1, 1997, and they were mandatory on new air-braked trailers and single-unit trucks and buses after March 1, 1998. New single-unit trucks and buses with hydraulic brakes had to be equipped with antilocks after March 1, 1999. This was not the first antilock standard for U.S. trucks. A federal brake standard took effect in 1975, but its antilock and stopping distance requirements were suspended after litigation in 1978.

    ABS is important for big trucks because of the poor braking capabilities of these vehicles compared with passenger cars. On dry roads, stopping distances for big trucks are much longer than those of passenger cars — 47 percent longer in Institute tests. Insurance Institute for Highway Safety. 1990. Special issue: Antilock brakes for trucks. Status Report 25(5):1-7. On wet and slippery roads, the stopping distance disparity is even worse. Tractor-trailer combinations also have the potential for loss of control and jackknifing, especially on slippery roads. (Jackknifing occurs when the rear wheels of a tractor lock up, allowing the tractor to skid and spin so that it folds into the trailer. This also can happen when trailer wheels lock and cause the trailer to swing around the tractor.) Antilock brakes not only reduce stopping distances on wet and slippery roads, but also help drivers maintain control.

    The standard for tractors requires antilock control on the front axle and at least one rear axle. On at least one of the tractor axles, each wheel must be independently controlled by an antilock modulator. This ensures that a wheel provides shorter stopping distances and optimal braking force on all surfaces, especially on roads where one side is slipperier than the other. For semi-trailers, at least one axle must have antilocks. Full trailers must have antilocks for at least one front and one rear axle.

    A 2010 report by the National Highway Traffic Safety Administration concluded that ABS on tractors reduced crash involvement by 3 percent. Allen, K. 2010. The effectiveness of ABS in heavy truck tractors and trailers. Report no. DOT HS-811-339. Washington, DC: National Highway Traffic Safety Administration. However, there was no significant effect on fatal crashes.