About this Article
Written by: Derek Nielsen
Written on: May 1st, 2013
Tags: computer science, electrical engineering, ergonomics, mechanical engineering, transportation
Thumbnail by: Yoichi R. Okamoto/Environmental Protection Agency
About the Author
Derek Nielsen is a mechanical engineering student in the class of 2015 at the Viterbi School of Engineering. His primary interests include automotive engineering and spacecraft design.
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Volume XV Issue III > Automotive Active Safety Systems
Automotive active safety systems have saved many thousands of lives since their introduction. From simple headlights to automated emergency braking, active safety systems use advances in engineering to make driving safer. By making a vehicle more visible to other drivers, better informing a driver of road hazards, and even taking total control of an automobile to prevent an accident, automotive active safety systems protect millions of people every day.


In the United States in 2011, there were an average of 82 fatal motor vehicle crashes every single day. These crashes resulted in a total of 32,387 deaths; in the same year, there were 5,338,000 motor vehicle accidents overall [1]. These shocking statistics plainly illustrate the often-underestimated​ danger inherent in driving a car. While these numbers are staggeringly high, fortunately they are in decline. In fact, the number of fatalities in 2011 was the lowest since 1949, despite many more miles being driven in total. Much of this steady reduction in the frequency and lethality of crashes can be attributed to the introduction and widespread adoption of new automotive safety technologies in the past few decades.
Automotive safety technologies can be divided into two basic categories: active and passive safety systems. Passive safety systems are those that reduce the severity of a crash once it has occurred; these include now-ubiquitous technologies such as airbags, seatbelts, and crumple zones. Active safety systems, on the other hand, are engineered to prevent accidents from occurring in the first place. This is accomplished through various methods, including making the vehicle more visible to other drivers, better informing the driver of road hazards, and even taking control of the automobile to prevent an accident. With technologies like enhanced headlights and radar-based collision avoidance, active safety systems represent a vitally important and rapidly developing branch of automotive engineering.

History of Automotive Active Safety Systems

When Karl Benz patented the automobile in 1886, active safety systems were, unsurprisingly, not part of his design. The original Benz Patent Motorwagen was little more than a motorized carriage, without even a simple headlight for visibility or conspicuity [2]. Interestingly, significant safety improvements over that very first automobile were almost nonexistent for several decades. Even rudimentary passive safety systems only began to be introduced in the early 1930s, with basic features like safety glass and padded dashboards gradually appearing in passenger cars [3]. It would take many more years before active safety systems began to be introduced in automobiles. With the exception of basic visibility devices such as headlights and mirrors, automotive active safety systems were nonexistent until the dawn of the computer age brought about transformational improvements in safety technology.
D. Sikes/Flickr
Figure 1: In recent decades, ABS and ESC have reduced the risk of automobile accidents, especially with difficult road conditions.
Made possible by the power of the miniaturized computer, the introduction of the anti-lock braking system (ABS) in the 1970’s and electronic stability control (ESC) in the 1990s revolutionized automobile safety. As one of the first safety systems to take corrective action and assist the driver with controlling the vehicle in unstable situations (like poor road conditions related to weather as in Fig. 1, for example) ESC had an especially significant impact. The Insurance Institute of Highway Safety (IIHS) found that ESC reduces the risk of single vehicle crashes by 40%, and reduces the risk of fatal crashes by a massive 56% [4]. These figures show the tremendous improvement that active safety systems offer, even in cars already protected by passive safety systems. However, as significant as these advances were, they only represent the beginning of the development of active safety systems. New technologies adopted in the last decade are once again causing a paradigm shift in automobile safety, affecting – and potentially saving – the lives of drivers around the world.

Situational Awareness

Improving the driver’s awareness of road hazards is the foundation of safe driving. If a driver is not informed quickly of potential dangers, reacting appropriately to them becomes more difficult and the probability of an accident occurring rises dramatically. Since improving the driver’s ability to anticipate danger has such potential to reduce the frequency and severity of accidents, some of the most effective modern automobile safety technologies function by enhancing the driver’s situational awareness.

Adaptive Headlights

Ironically, one of the most effective active safety technologies employed in vehicles today is based on the most basic of active safety devices: the headlight. Along with making the vehicle highly visible to other drivers, headlights serve a simple purpose: illuminating the road ahead at night. However, standard headlights only light up the terrain directly ahead of the car; there is an unavoidable reduction in visibility when driving into a curve (Fig. 2) as the light points uselessly off the outside of the bend. This loss of visibility can lead to a dangerous situation if there is an obstacle in the curve that is not illuminated in time for the driver to react.
Sebastian Ballard/​.uk
Figure 2: Narrow, curved roads can pose great danger to those automobiles not outfitted with adaptive headlights.
However, automakers have devised an effective solution to this dangerous shortcoming: adaptive headlights. Adaptive headlights turn to illuminate the vehicle’s path whenever it turns, allowing the driver to see into curves when driving at night. This is accomplished by housing the headlight in an assembly that can be rotated horizontally by small electric motors to point the headlights in the vehicle’s direction of travel. By rapidly processing information such as steering wheel angle, yaw, and the speed of the vehicle, adaptive headlights can anticipate where the car is going and direct the light accordingly. Adaptive headlights anticipate the path of the vehicle and turn to illuminate curves in the road ahead.
While this improvement in visibility may seem minor, real-world data indicates that adaptive headlights are a highly effective safety feature. In a study conducted by the IIHS, adaptive headlights were responsible for a 10% reduction in accidents in cars equipped with them [5]. If every car on the road were equipped with adaptive headlights, approximately 142,000 crashes could be prevented every year [6]. Clearly, the improvement in visibility has a significant positive effect on safety, but adaptive headlights only work at night. Other active safety systems must be utilized to warn drivers of the hazards that can escape the attention of a driver even in broad daylight.

Blind Spot Information System

A vehicle’s blind spot represents a treacherous gap in a driver’s situational awareness. The blind spot is defined as the area around the vehicle that is obscured from the driver’s view. In passenger vehicles, this is most commonly the hidden area that lies between the field of view of the rear view mirror and side view mirrors. If a driver is unaware that there is another vehicle hidden in the car’s blind spot and changes lanes suddenly, a collision is likely to result. A recently developed protection against this threat is the blind spot information system (BLIS). This active safety system uses cameras on the side of the car to detect the presence of other vehicles within the car’s blind spot and alerts the driver to their presence with a warning light on the corresponding side of the car. If the driver activates the turn signal on the side of the car where the unseen hazard is lurking, a more intrusive audio, visual, or haptic warning is issued to urgently discourage the driver from changing lanes.
The blind spot information system is a valuable addition to the driver’s own visual inspection of the surrounding road. However, as useful as warning technologies like BLIS can be in preventing accidents, a new generation of active safety technologies aims to make driving safer than ever by correcting for the vehicle’s most unreliable element: its human driver.

Driver Assistance

Technologies such as the blind spot information system and active steering headlights certainly make driving a safer endeavor, but they have a major shortcoming; the driver alone bears the responsibility for taking action to avoid a dangerous situation. While keeping drivers informed of their surroundings on the road makes a vital contribution to safety, human error often results in an accident despite the frantic warning of active safety systems. This is the impetus behind the rise of driver assistance systems: technologies that not only warn the driver of hazards, but also have the capability to take partial control of the vehicle to prevent a collision.

Collision Avoidance System

Rear-end collisions are the most frequently occurring type of accident, and they are also often easily preventable [7]. In many cases, a distracted driver will simply fail to notice that the leading car has slowed or stopped and crash into it, which could be deadly for either driver involved at sufficient speeds (Fig. 3). The technology that was developed to prevent this is known as the collision avoidance system. Collision avoidance systems utilize a radar unit mounted in the front of the vehicle to track the distance and speed of the leading car. If the radar senses that the leading car is slowing rapidly, a warning will sound to encourage the driver to brake. If no action is taken and the distance between the two vehicles is decreasing quickly enough to make an accident inevitable, the system will automatically apply the vehicle’s brakes to prevent the collision or at least reduce its impact. It is estimated that collision avoidance would be helpful in 1.2 million accidents per year, including 66,000 crashes resulting in serious or moderate injury and 879 fatal crashes [6]. As effective as collision avoidance systems may be, they only serve to prevent one driver from rear-ending another. Automobiles must rely on another active safety system to protect against more drastic driver errors.
W. Robert Howell/Flickr
Figure 3: Dangerous (and potentially life-threatening) collisions at high speeds can be prevented or mitigated with collision avoidance systems or lane departure prevention.

Lane Departure Prevention

While they may not be as common overall as rear-end collisions, a large proportion of fatal crashes are caused by a vehicle leaving the roadway and colliding with another vehicle head-on [5]. Because of the extreme damage and injury characteristically caused by these collisions, automotive engineers have developed an active safety system that can literally take the wheel to prevent an imminent accident. Lane departure prevention is a driver assistance system that uses cameras mounted in front of the rear-view mirror to monitor lane markings on the road ahead. If the system senses that the car is drifting out of its lane without a turn signal activated, the driver will be warned by a combination of lights, sounds, and vibration in the seat or steering wheel that is reminiscent of driving over a rumble strip. If no corrective action is taken, the lane departure prevention system can take over the vehicle’s electromechanical steering mechanism, turn the steering wheel, and stay in the lane. The IIHS estimated that 7,529 fatal crashes could be prevented every year if all cars were equipped with lane departure warning alone, with far more prevented if lane departure prevention were included as well [5].


While these automotive driver aids undoubtedly have the ability to save lives and to reduce injury and property damage, they are not without their limitations. One factor that reduces the effectiveness of active safety systems is the inconsistency of real-world road conditions. For example, a modern lane-keeping system will only be functional on a road with clear lane markings. In a study conducted by the National Highway Safety Association, the lane departure warning system being tested was available 76% of the time on freeways, and only 36% of the time on non-freeways [8]. Some of these safety systems are also very expensive, particularly ones that rely on specialized hardware, such as thermal cameras or radar range finders. The prohibitively high cost limits the impact of some safety technologies because they are initially only available on high-priced luxury models that sell in lower volumes. Finally, there may be some resistance from the public to systems that intrusively warn of hazards or take control of the vehicle to prevent collisions. Active safety systems must be diligently and responsibly designed to minimize false alarms and unnecessary intervention; otherwise, the potentially life-saving technology may simply be deactivated.

Future Developments

With the proliferation of computerized safety systems, the gradually declining cost of components, and the adoption of new technologies such as light detection and ranging (LIDAR), automotive driver aids are simultaneously advancing rapidly in their capabilities and becoming standard on more and more new vehicles. One of the biggest areas for future improvement of driver aids is cost; the more affordable these life-saving systems are, the more cars they will be included in, and the more drivers will benefit from their protection. The effectiveness of existing active safety systems will also continue to improve in the future, as technologies underlying computer vision and artificial intelligence are developed further. For example, a lane keeping system that is only active 36% of the time on non-highways stands to be improved dramatically by more sophisticated image processing software.
Along with the cost reduction and performance improvement of current active safety systems, there is an entirely new category of active safety systems being developed. Known as vehicle-to-vehicle and vehicle-to-infrastru​cture systems, these technologies capitalize on the recent explosion of Internet connectivity to make driving even safer. One theoretical implementation of these systems would be a “road-train” of cars on a freeway, all communicating constantly with each other. Because of this close cooperation, the vehicles would all travel close together at the same speed, independent of driver input. If the lead car applied the brakes, every car in the train would be instantly notified and could slow automatically. Such a system would improve safety and fuel economy while making freeway travel more convenient. Another promising possibility is a system in which the driver is informed of when upcoming traffic signals will change by the road infrastructure itself, allowing them to safely anticipate when they will have to stop.
While the troubling statistics for automobile accidents are trending downwards, there are still tens of thousands of deaths every year that can be prevented by well-engineered safety solutions. As these technologies become more and more common, there will be an ever-growing group of people that owe their lives to the protective power of automotive active safety systems.


    • [1] (2012, Dec.). 2011 Motor Vehicle Crashes: Overview [Online]. Available: http://www.nrd.nhtsa​​.pdf
    • [2] K. F. Benz, "Fahrzeug mit Gasmotorenbetrieb," German Patent 37435, Jan. 29, 1886.
    • [3] Appointments of the new Ford [Online]. Available: http://www.oldcarbro​​/Ford/1930_Ford/1930​_Ford_Brochure_02/19​30%20Ford-14-15.html​
    • [4] (2006, June 13). Electronic stability control could prevent nearly one-third of all fatal crashes and reduce rollover risk by as much as 80% [Online]. Available:​news/rss/​ml
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    • [8] B. H. Wilson et al., “Evaluation of a Road-Departure Crash Warning System,” NHTSA, Washington, DC, Rep. DOT HS 810 854, Dec. 2007.