Q&A: Crash avoidance technologies

March 2013

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. Using the information they gather, these technologies warn the driver when they detect the potential for 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?

There are many vehicle features that could be considered crash avoidance technology. This list summarizes some of the most common or promising systems. This is not a comprehensive list of technologies, as more are being developed and introduced each year. The descriptions are general and may not capture every variation of a given technology.

Forward collision avoidance systems alert the driver when the vehicle is getting too close to one in front of it. Most systems precharge the brakes to maximize their effect if the driver responds to the warning. Some systems are able to brake the vehicle autonomously if the driver doesn't respond. These systems use various types of sensors, such as cameras, radar or light detection and ranging (LIDAR) to detect vehicles or objects in front of the vehicle. A forward collision warning system with autonomous braking may not always be able to prevent a crash but may reduce vehicle speed, mitigating the severity of the crash.

Pedestrian detection is a subset of forward collision avoidance that is designed to recognize pedestrians. These systems use advanced algorithms coupled with some combination of sensors and cameras to spot people who are in or about to enter the vehicle's path.

In addition to providing driver warnings and/or autonomously braking, some forward collision avoidance systems may perform other functions to potentially reduce the severity of an imminent collision, including pretensioning safety belts, closing windows or adjusting seat positions or head restraints. These actions may help reduce the likelihood of injury if a crash occurs.

Another related feature is adaptive cruise control, which is typically marketed as a convenience feature. As with regular cruise control, the driver sets the desired speed. The difference is that the vehicle automatically slows down in heavy traffic in order to maintain a safe gap without the driver having to do anything. 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, the vehicle accelerates to maintain the preset cruise speed. Some systems allow drivers to adjust this gap, resulting in smaller or larger following distances. If the vehicle slows below a certain speed as it approaches another vehicle, some systems are designed to disengage and require the driver to resume control, while others can bring the vehicle to a complete stop.

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.

Lane departure warning and prevention 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. 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 sideview 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 on the turning side. 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, and radar or ultrasonic systems warn the driver of objects behind the vehicle. Some systems will even automatically apply the brakes to keep the vehicle from backing into or over an object. A cross-traffic alert system uses sensors to detect approaching vehicles that may cross the path of a vehicle backing up, warns the driver of their presence, and may automatically apply the brakes to prevent a collision. Some parking assist systems also are capable of automatically parallel parking the vehicle.

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

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.

Curve speed warning systems use a combination of GPS and digital maps to monitor vehicles as they approach bends in the road. If the system detects that the vehicle is approaching a curve at an unsafe speed that may result in a loss of control, it alerts the driver.

Fatigue warning systems use sophisticated algorithms that monitor driver steering and other behaviors. Some may monitor the driver's eye blink rate and blink duration. A system will alert the driver if it detects inattention or drowsiness.

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 vehicle's brakes and modulates the engine power to keep the vehicle traveling along the path indicated by the steering wheel position.

See electronic stability control Q&A.

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.

See antilock brakes Q&A.

3 How widely available are these 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. Information by make and model on the availability of forward collision warning, autonomous braking, lane departure warning, lane departure prevention, adaptive headlights and blind spot detection can be found here.

The federal government has recognized the potential importance of forward collision avoidance and lane departure warning by incorporating them into its New Car Assessment Program. Vehicles are credited with having one of these systems if their system can pass specified track tests. However, at this time there are no definitive studies indicating that systems that don't pass the tests are ineffective or that ones that do pass the tests are working better to reduce real crashes.

As of the 2012 model year, the government requires ESC on new passenger vehicles. Information on which models from previous years are equipped with ESC can be found here.

4 Do crash avoidance features reduce crashes?

The jury is still out on many advanced crash avoidance technologies, which haven't been around long enough for researchers to analyze their effectiveness. However, a few systems look promising, based on early indications from insurance claims data.

Volvo's City Safety, a low-speed forward collision avoidance system, is one feature that has been shown to be effective. The system is designed to help a driver avoid rear-ending another vehicle in slow-moving traffic. The Highway Loss Data Institute (HLDI) examined insurance claims for 2010 Volvo XC60 SUVs equipped with City Safety and compared them with claims for other 2009-10 midsize luxury SUVs. The XC60s had 27 percent fewer claims under property damage liability coverage, which pays for damage to vehicles that an at-fault driver hits. There also were fewer claims under bodily injury liability coverage (for injuries to people in other vehicles) and collision coverage (for damage to the insured vehicle). Highway Loss Data Institute. 2011. Volvo City Safety loss experience — initial results. Loss Bulletin Vol. 28, No. 6. Arlington, VA.

In a separate analysis of forward collision avoidance systems that function at higher speeds, HLDI found 14 percent fewer insurance claims under property damage liability coverage for Acura and Mercedes-Benz vehicles with forward collision warning with autonomous braking than for the same vehicles that weren’t equipped with the technology. Insurance Institute for Highway Safety. 2012. They’re working: insurance claims data show which new technologies are preventing crashes. Status Report 47(5):1-7. Mercedes offers a version of forward collision warning that does not include autonomous braking, which also showed lower crash rates but not to the same extent as the version that includes it. Systems without autonomous braking probably have more modest benefits because they rely on drivers to respond appropriately to warnings and can’t directly avoid crashes.

Adaptive headlights were also found to be effective in HLDI’s analysis, even beyond what researchers expected. HLDI looked at adaptive headlights offered by Mazda, Mercedes and Volvo and found property damage liability claims fell as much as 10 percent with adaptive headlights. That was surprising, since only about 7 percent of police-reported crashes occur between 9 p.m. and 6 a.m. and involve more than one vehicle. An even smaller percentage are multiple-vehicle, nighttime crashes occurring on a curve, where adaptive headlights would be expected to have an effect. It’s possible that other differences between the adaptive headlights and conventional ones besides steerability — for example, brightness or beam pattern— may have played a role in reducing crashes with other vehicles. However, those differences weren’t consistent among all vehicles in the analysis.

There is more evidence available for systems that have been around longer, such as ESC.

ESC is effective in reducing crashes. Institute researchers have found it reduces fatal single-vehicle crash risk by 49 percent and fatal multiple-vehicle crash risk by 20 percent for cars and SUVs. Farmer, C.M. 2010. Effects of electronic stability control on fatal crash risk. Arlington, VA: Insurance Institute for Highway Safety.

On the other hand, antilock brakes are an example of a technology that hasn't panned out as expected. For reasons not completely understood, antilock brakes haven't had a significant effect on passenger vehicle crashes.

5 If the new technologies work as intended, how many crashes could they potentially prevent or mitigate?

If all passenger vehicles were equipped with forward collision warning, lane departure warning, blind spot detection and adaptive headlights, about 1 in 3 fatal crashes and 1 out of 5 injury crashes could potentially be prevented or mitigated. Jermakian, J.S. 2011. Crash avoidance potential of four passenger vehicle technologies. Accident Analysis Prevention 43(3):732-40.  Those numbers are from an Institute analysis of 2004-2008 crash data and represent the best-case scenario, presuming the systems perform as advertised and drivers respond to them correctly. They reflect known limitations of crash avoidance systems available at the time of the study. However, they don't take into account potential reductions in effectiveness due to driver interactions with the systems or increased effectiveness due to enhanced system capabilities. Of all four features, current forward collision warning systems have the potential to prevent or mitigate the most crashes, and lane departure warning could come into play in the most fatal crashes.

Another Institute study looked at crash avoidance technologies in large trucks. Based on an analysis of 2004-2008 crashes, it found that blind spot detection, forward collision warning, lane departure warning and ESC together could prevent or mitigate as many as 28 percent of large truck crashes a year, including 1 out of 5 fatal ones. Jermakian, J.S. 2012. Crash avoidance potential of four large truck technologies. Accident Analysis and Prevention 49:338-46.  Of the four technologies, blind spot detection is applicable to the largest number of crashes. ESC showed the most potential for fatal crashes, possibly preventing or mitigating 15 percent of fatal large truck crashes each year.

Several studies have looked at performance of these systems through field operational tests. A prototype forward collision warning system without automatic braking for passenger vehicles was field tested by 66 drivers for four weeks each. Based on the number of near-crash scenarios identified, the system was projected to reduce rear-end collision rates by 10 percent. Najm, W.G.; Stearns, M.D.; Howarth, H.; Koopmann, J.; and Hitz, J. 2006. Evaluation of an automotive rear-end collision avoidance system. Report no. DOT HS-810-569. Washington, DC: National Highway Traffic Safety Administration.

A field operational test conducted in 2004 and 2005 looking at lane departure warning and curve speed warning systems estimated an annual reduction in road-departure crashes of 9,400 to 74,800 if all passenger vehicles were equipped with these systems and they worked as intended. During the field test, these systems weren't operational 45 percent of the time because of weather and other factors. At that rate, the total reduction in crashes drops to an estimated 5,200 to 41,200. Wilson, B.H.; Stearns, M.D.; Koopmann, J; and Yang, C.Y. 2007. Evaluation of a road-departure crash warning system. Report no. DOT-HS-810-854. Washington, DC: National Highway Traffic Safety Administration.

As crash avoidance technologies become increasingly common, more data will be available to determine how effective these systems really are in preventing or mitigating crashes.

6 How do drivers respond to new crash avoidance features?

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.

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, are overwhelmed by them, or don't take an appropriate corrective action, then the systems will be ineffective. 

A 2012 Institute survey of owners of Volvo vehicles with crash avoidance technologies found that, despite some annoyance, the majority of 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. Eichelberger, A.H. and McCartt, A.T. 2012. Volvo drivers' experiences with crash avoidance and related technologies. Arlington, VA: Insurance Institute for Highway Safety.  Respondents were owners of vehicles equipped with City Safety, which is standard on select vehicles; an optional technology package that included adaptive cruise control, forward collision warning with auto brake, lane departure warning and a fatigue warning system; or both.

One concern was that drivers might rely on the systems too much and feel freer to look away from the road or take other risks. 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 allowing the vehicle to brake for them at least some of the time. About one-third of owners experienced autonomous braking when they believed they were at risk of crashing, and about one-fifth of owners thought it had prevented a crash.

Drivers who participated in a field operation test of multiple crash avoidance technologies had favorable opinions of them. Seventy-two percent of the drivers said they would like to have the crash avoidance technologies in their personal vehicles. Sayer, J.R.; Bogard, S.E.; Buonarosa, M.L.; LeBlance, D.J.; Funkhouser, D.S.; Bao, S.; Blankespoor, A.D.; and Winkler, C.B. 2011. Integrated vehicle-based safety systems light-vehicle field operational test key findings report. Report no. DOT HS-811-416. Washington, DC: National Highway Traffic Safety Administration.  Drivers preferred the lane departure warning and blind spot detection technologies over the forward collision warning and curve speed warning technologies, in part because they issued fewer false warnings. Drivers reported that they didn't rely on the technologies, and no increased involvement in distracting tasks such as eating or talking on a cellphone was observed.

Truck drivers who participated in a field operational test of multiple crash avoidance technologies also had favorable opinions of the technology. Fifteen out of the 18 drivers preferred driving a truck equipped with the crash avoidance technologies over a conventional truck and stated that the technologies made them more aware of the environment around the vehicle as well as their position in the lane. Sayer, J.R.; Bogard, S.E.; Funkhouser, D.; LeBlanc, D.J.; Bao, S.; Blankespoor, A.D.; Buonarosa, M.L.; and Winkler, C.B. 2010. Integrated vehicle-based safety systems heavy-truck field operational test key findings report. Report no. DOT HS-811-362. Washington, DC: National Highway Traffic Safety Administration.  There was no observed increase in a driver's likelihood of engaging in distracting tasks while driving trucks equipped with crash avoidance technologies. A few drivers began ignoring warnings as a result of a high number of false alarms.

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

Many crash avoidance technologies rely on drivers to take action. The effectiveness of these systems depends on whether drivers accept the technologies, understand the information from the system and respond appropriately. This is especially true for warning systems, since a warning is useless if it's ignored. If drivers find the systems annoying, overwhelming or unhelpful, they may disable them. Plus, 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 rely on the ability of the sensors to register lane markings, which may be problematic on roads that aren't well marked or are covered with snow. In a field test of a prototype road departure warning system, the system was available 76 percent of the time on freeways compared with 36 percent of the time on non-freeways. Sensors such as cameras, radar and LIDAR also may be influenced by environmental factors such as lighting or precipitation. In the same study, the lane departure warning system was available 56 percent of the time during dry, daytime conditions and only 4 percent of the time during wet, nighttime conditions. Wilson, B.H.; Stearns, M.D.; Koopmann, J; and Yang, C.Y. 2007. Evaluation of a road-departure crash warning system. Report no. DOT-HS-810-854. Washington, DC: National Highway Traffic Safety Administration.  Most current systems struggle to detect the outside environment in low light or inclement weather. Sayer, J.R.; Bogard, S.E.; Funkhouser, D.; LeBlanc, D.J.; Bao, S.; Blankespoor, A.D.; Buonarosa, M.L.; and Winkler, C.B. 2010. Integrated vehicle-based safety systems heavy-truck field operational test key findings report. Report no. DOT HS-811-362. Washington, DC: National Highway Traffic Safety Administration.

Some systems only work at certain speeds. Other systems don't operate until turned on by the driver. Systems that rely on GPS to monitor the car's location, such as curve speed warning, are limited by the accuracy and availability of the digital maps.

8 What other kinds of crash avoidance 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 are prototype safety systems in which vehicles and roadway infrastructure communicate over a wireless network. Drivers can then use this information to help avoid crashes.

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.

Beginning in 2012, a year-long pilot study in Ann Arbor, Mich., will test the functionality and reliability of these connected vehicle technologies. More than 70 lane-miles of urban, suburban and rural roads and nearly 3,000 vehicles, including passenger cars, commercial trucks and transit buses, will be equipped with the V2V and V2I technology, enabling wireless communication between vehicles and infrastructure. This study will further understanding of the potential effectiveness of connected vehicle technologies in reducing crashes. 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.

These technologies, along with other in-vehicle systems to control the engine, brakes and steering, could lead to more autonomous driving.