Accident Research - Reality Is the Benchmark: Accident Research as a Basis for Improving Safety

Jun 15, 2007
  • Systematic accident research at Mercedes since 1969
  • To date, some 3,800 serious road-traffic accidents reconstructed and analyzed
  • New Mercedes safety systems based on real-life accident research
On a cold, gray winter's day in January 1969, government officials and senior police officers from Baden-Württemberg met up with representatives of the then Daimler-Benz AG for several hours of talks at the state's Interior Ministry. On the agenda was an unusual request on the part of the automotive company - an appeal for police assistance in reconstructing and analyzing road-traffic accidents involving Mercedes models.
The idea of the development engineers was to use data from real-life accidents in order to enhance vehicle-occupant safety. Daimler-Benz had already acquired initial experience in this field during a six-month pilot project held two years previously. During the period January - June 1967, company employees had worked together with police on the investigation of serious road-traffic accidents that had occurred in the district of Böblingen and on the A8 highway.
The prime aim of the meeting at the Ministry was to place this research project on a broader and, most important of all, permanent footing. The reaction was positive, and senior police officers once again signaled a readiness to cooperate. A communiqué was therefore dispatched to the various departments with a request for support. The Accident Research Project was officially launched on April 29, 1969, after which the Interior Ministry issued a directive to all the relevant police departments, ordering them to inform Daimler-Benz by telephone of any road-traffic accidents and to allow company representatives to inspect the accident report and question the duty officers on the actual sequence of events. The justification for this measure was as follows: "The Interior Ministry supports the research of Daimler-Benz AG because of its general import for road safety."
Thanks to successful cooperation with the authorities and the police, the area covered by the Mercedes accident research would expand several times over the following years. Today, it stretches from Baden-Baden to Ulm, from Mannheim to Albstadt, and from Tauberbischofsheim to Freudenstadt - almost 200 kilometers across at its widest point.
When Mercedes started systematic accident research in spring of 1969, this type of work was still rare in Germany. It was only in 1970 that the German Parliament resolved to set up a central unit at the Federal Highway Research Institute that would be concerned specifically with the crucial task of accident investigation. A study project entitled "Accident Scene Statistics" was launched in 1973 by a research team from Berlin Technical University and Hanover Medical School. Today, it bears the name of "GIDAS" ( German In- Depth Accident Study) and annually provides data from around 2,000 road-traffic accidents occurring in the vicinity of the cities of Hanover and Dresden. Such data are representative for Germany, and the Mercedes Accident Research department works closely with the GIDAS project.
Accident researchers on call
Thirty-eight years of accident research at Mercedes translates into 38 years of meticulous data acquisition and detailed analysis. Today, researchers are called out around 80 times a year to carry out first-hand inspection of serious crashes. Since being set up, Mercedes Accident Research has investigated and reconstructed more than 3,800 traffic accidents.
At the scene of the accident, work generally begins with a set of basic questions: How did the accident happen? What was the position of the vehicles after collision? Are there any brake or skid marks? How badly have the body shells been deformed? Were airbags and seatbelt tensioners activated? Is there anything unusual about the interior of the crashed Mercedes model? Were the occupants injured - and if so, what were their injuries?
The answers to all these questions and more are ultimately recorded in an 80-page accident report, which also includes dozens of photos, sketches and eye-witness accounts. Once the relevant information has been collated, researchers can set about systematically reconstructing the actual collision. They are assisted by a computer system that converts data and measurements gathered at the scene of the accident into moving images. By combining, for example, the length of the brake or skid marks with design data and information on the handling behavior of the damaged Mercedes model, the computer is able to reconstruct the actual sequence of events involved in the accident. Researchers can then view onscreen how the vehicle moved before, during and after the collision. What's more, the computer simulation also provides views of the accident from different perspectives.
The results are then compared with data from other accidents, thus enabling automotive engineers to gradually compile an exact picture of the typical injuries involved, and acquire the knowledge needed to develop new and even more effective safety systems. Furthermore, the findings of Mercedes Accident Research show the engineers that the brand's longstanding and uncompromising stance on safety is already paying dividends, as analyses of traffic accidents show that the risk of being injured when traveling in a Mercedes sedan has been consistently declining for many years now. 
Technological edge through research
The many years of accident research at Mercedes-Benz have played a major role in preserving the brand's technological edge over rival automakers. That's because engineers in and are quick to apply this knowledge in a practical manner. Over the years, the findings of such research have repeatedly provided the basis for the development of new and pioneering safety systems:
  • Interior design
At the end of the 1960s, when Mercedes-Benz first began systematic accident analysis, experts initially focused on improving protection inside the passenger compartment. Although Mercedes models were already then fitted with seatbelts, very few people actually bothered to use them. For many front-seat passengers, this carefree attitude led to serious head injuries, resulting from an impact with the steering wheel, instrument panel or windshield. Accident researchers therefore set about identifying dangerous impact points inside the vehicle and suggested improvements to the design of various switches and handles responsible for severe injuries. Likewise, the instrument panel and interior trim materials were also reconsidered with safety in mind. Since then, design engineers have favored energy-absorbing materials.
  • Test procedures and body structure
Once the interior had been made safe, the attention of accident researchers and engineers turned toward improving the body structure. Once again, this followed on from initial accident analyses. Although 51 percent of all serious passenger car accidents involve a head-on collision, experts have known since the beginning of the 1970s that the reality behind this term is often much more complex than it seems.
When reconstructing typical collisions with oncoming traffic, accident researchers quickly realized that vehicles usually hit one another asymmetrically, with the result that the front part of the body is more heavily impacted on one side. Experts describe this type of crash as an offset collision. In around half of all so-called head-on collisions on German roads, the impact actually affects only 30 to 50 percent of the left-hand side of the vehicle front. In a further 25 percent of such collisions, the impact occurs on the passenger side of the vehicle front.
This discovery had major consequences for automotive design. Given that a full front-end collision against a flat wall - legally required as a safety test for passenger cars - only represented a fraction of real-life accidents, Mercedes-Benz decided to go it alone. On the basis of results from the company's own accident research, engineers introduced the first offset crash tests as early as 1974 and went on to develop a design principle that provides high occupant safety even when the vehicle front is subject to extreme partial loads. The solution came in the form of forked members - rigid longitudinal sections on both sides of the front part of the body structure, each of which forks in front of the front wall and toward the side skirts and the drive shaft hump. These cause the force of impact from a collision to spread equally between the hump, floor and side panel, with the result that the passenger compartment remains largely undamaged. The S-class sedans of the W 126 series, as launched in 1979, were the first Mercedes models to feature forked members designed specifically to protect against offset front-end collisions. Today, a new design principle provides even more effective protection for vehicle occupants - and not only in the event of an offset crash.
Years of continuous accident observation later revealed the need for a further modification of the test procedure, whereupon Mercedes-Benz developed the offset crash test against a deformable barrier. Here, an aluminum structure serves to replicate the crash crumple zone of the opposing vehicle, thereby enabling a more realistic analysis of how the body deforms during impact than is the case with a collision against a rigid concrete or steel barrier. Jointly developed by Mercedes-Benz, the crash test with a deformable barrier is now part of Euro NCAP (New Car Assessment Program) and, as such, compulsory for all new passenger cars in Europe.
  • Seatbelts
Further analysis of real-life accidents in the 1970s and '80s led to the development of additional pioneering safety features. The most important of these was the three-point seatbelt, which was first introduced by Mercedes-Benz in 1968 and, along with headrests for the driver and front-seat passenger, became standard equipment in all the brand's models in 1973. The seatbelt remains the most important element of occupant safety and has saved hundreds of thousands of drivers and passengers from death or serious injury over the years.
Once again, however, accident research showed Mercedes engineers that there was still room for improvement. This included enhanced seatbelt geometry and fixing the lower mounting point to the frame of the seat. This ensures optimal positioning of the seatbelt irrespective of the seat's position. In 1971, the Mercedes-Benz 280 SL debuted as the world's first car to feature this important safety feature.
  • Seatbelt tensioners
It was in the early 1970s that accident researchers first realized that conventional seatbelts were not sufficient to protect vehicle occupants from impact with the steering wheel or instrument panel in the event of a severe front-end collision. The reason for this was the slack in the seatbelt, which results from the design principle of the component, and which Mercedes engineers were able to offset with the invention of the seatbelt tensioner. In the event of a crash, the tensioner tightens the seatbelt in a matter of milliseconds. Development of this practical component began in 1970. Yet it was only with subsequent advances in microelectronics, which are required to trigger its mechanism, that the seatbelt tensioner achieved a realistic chance of entering series production. Mercedes-Benz first introduced seatbelt tensioners for the front seats in 1980, and they have been standard equipment in all the brand's passenger car models since 1984.
Today, there is no doubt as to whether this complex development was worthwhile. In the event of a front-end collision, the seatbelt tensioner not only prevents the head and upper body from tilting dangerously forward but also reduces the overall stress load on vehicle occupants.
  • Airbag
The quality of occupant restraint systems was further enhanced by the development of the airbag - another flash of inspiration on the part of Mercedes engineers and a milestone in safety technology. Development of this pioneering piece of equipment began in 1967. It was patented by Daimler-Benz in October 1971 (DE 2152902 C2) and first introduced into series production at the end of the 1980s, following a full 13 years of development and testing. The airbag inflates within milliseconds of a front-end collision to prevent the driver's head from hitting the steering wheel or instrument panel, thus substantially reducing the risk of serious injury. Mercedes-Benz has fitted a driver airbag as standard equipment since 1992.
With the launch of the S-class (W 220 series) in 1998, Mercedes engineers showed that the airbag can be tailored to deal with different accident situations. The engineers developed an innovative two-phase gas generator that enables the airbag to be inflated in line with the severity of the impact: If the sensor system registers a medium collision, it activates merely the first phase of the gas generator, with the result that the airbag is only partially inflated. If, however, a more severe impact is detected, the first phase is followed milliseconds later by a second phase that further inflates the airbag. This adaptive control system for both the driver and front-seat passenger airbag is today a standard feature of all Mercedes passenger cars.
From the word go, Mercedes engineers had designed the airbag to supplement the three-point seatbelt, the primary function of which is to provide protection in the event of a front-end collision. Accident research at Mercedes-Benz confirms the wisdom of this approach. Back in the 1970s, around 30 percent of Mercedes car drivers involved in a severe front-end collision suffered life-threatening injuries despite wearing a seatbelt. Today, however, injuries of such a severity are a thing of the past thanks to the excellent interplay between airbag, seatbelt, seatbelt tensioner and other safety systems.
If these Mercedes accident research results are extrapolated to cover all passenger cars fitted with this technology, it means that the airbag has helped save the lives of more than 2,500 people in Germany alone since 1990. The National Highway Traffic Safety Administration in the United States has ascertained that airbags protect one in three car occupants against serious injury in the event of an accident. Moreover, around one in six drivers and front-seat passengers involved in an accident owe their lives to airbags. Indeed, the airbag has saved the lives of more than 14,200 vehicle occupants in the U.S. since 1987.
  • Seatbelt force limiters
In the mid-1990s, the analysis of accident reports revealed that standard fitting of airbags and seatbelt tensioners for drivers and front-seat passengers had created scope for further fine-tuning of the restraint system as a whole. In response, Mercedes-Benz developed the seatbelt force limiter, which reduces the restraining force of the seatbelt as soon as vehicle occupants are cushioned by the airbags. This significantly lessens the load on the upper body of front-seat passengers.
  • Sidebags and windowbags
Mercedes-Benz's longstanding commitment to enhancing occupant safety has had a huge impact: By early 1998, accident researchers were already able to confirm that the risk of suffering life-threatening or fatal injuries in the event of a front-end collision had been substantially reduced over the preceding two decades. Indeed, fatalities among passenger car occupants wearing a seatbelt were almost exclusively limited to extremely severe front-end collisions.
The focus therefore shifted to another type of accident: the side-on collision. The proportion of such collisions among all accidents resulting in serious injury to vehicle occupants has risen continuously since the 1990s. Although only 14 percent in 1985, it had risen to 30 percent by 1995. Similarly, side-on collisions were becoming an increasingly significant cause of fatalities among vehicle occupants: A study by Mercedes Accident Research actually revealed the proportion of all road traffic fatalities involving this type of collision to be 44 percent.
In response to this trend, safety engineers put together a package of measures that included not only stronger door locks and hinges but also special deformable elements and foam padding in the interior trim of vehicle doors. In addition, Mercedes passenger cars were fitted with protective reinforcement in the lower part of the doors. This protection against side impact was further enhanced with the introduction of sidebags in 1995 and windowbags in 1998.
The development of the windowbag was based on intensive research at Mercedes-Benz, which had shown that side-on collisions can lead to serious head injuries, either because occupants are struck by foreign objects entering the vehicle or because the force of the impact causes passenger heads to move outward. A large windowbag, which is inflated along with sidebags and covers the inner surface of the side window, provides effective prevention against this type of injury. Mercedes-Benz also developed a similar safety system for its roadsters and convertibles, as well as for the compact A-Class. Such models are fitted with special head/thorax sidebags to protect the upper body and head of front-seat passengers.
Thanks to automatic seatbelts, seatbelt tensioners, airbags and many other innovations, Mercedes models have reached such a high level of safety in recent years that it is virtually impossible to better this with technology already available. In other words, new ideas and approaches are required to achieve further advances in occupant safety. Once again, accident research has provided the necessary impetus: Some time ago, experts determined that over two-thirds of all traffic accidents are preceded by a critical driving situation such as skidding, emergency braking, or sudden evasive action - situations that already indicate an imminent collision. In the past, these precious few seconds before the crash could not be utilized for the benefit of passive occupant safety. That's because established protection systems such as seatbelts, airbags and seatbelt tensioners would only engage after impact.
Such insights from accident research led to the development of PRE-SAFE®, an innovative occupant protection system that ushered in a new era in vehicle safety at the end of 2002, and which has since won a number of awards for Mercedes-Benz. PRE-SAFE® is a preventive system that can anticipate an impending accident and immediately go into action to prepare the vehicle and its occupants for a possible collision by initiating a precautionary tightening of the seatbelts, for example. It thus makes the best possible use of the brief period before a collision to initiate a variety of preventive safety procedures. A comparison with nature is apt here: PRE-SAFE® gives the car "reflexes."
PRE-SAFE® is able to recognize an impending accident because it offers a unique synergy of active and passive safety features. It is networked to Brake Assist and the Electronic Stability Program (ESP®) - standard safety systems whose sensors recognize potentially dangerous driving situations and then transmit this information to their control units within milliseconds. Mercedes-Benz also uses this data for the purposes of anticipatory occupant protection, thus creating a new dimension in automotive safety.
  • NECK-PRO headrests
A further advanced safety development from Mercedes-Benz is known as NECK-PRO. This is a new type of headrest, likewise developed on the basis of an analysis of real-life accident situations. NECK-PRO provides effective reduction of the risk of injury to the cervical vertebrae in the event of a head-to-tail collision. These so-called whiplash injuries, caused by the sudden jolting movement of the head and the resulting strain on the cervical vertebrae, are one of the most common types of accident injury and, according to estimates of the EU Commission, generate costs of around €8 billion annually.
NECK-PRO is a sensor-controlled, crash-responsive headrest that is activated in the event of a head-to-tail collision. As soon as the sensors detect an impact of a predefined severity, the system releases pre-tensioned springs inside the headrests. These move the padded surface of the head restraints forward by around 40 millimeters and upward by 30 millimeters in a fraction of a second, thus providing enhanced support for the heads of front-seat passengers in advance of the impact, as well as preventing strain on the cervical vertebrae during a collision.
  • Details
A range of other technical innovations also contributes to the exemplary safety of Mercedes passenger cars. Although rarely mentioned and literally hidden away under the body shell, they are no less important in terms of occupant protection than innovations such as NECK-PRO, PRE-SAFE®, seatbelt tensioners or airbags. Many of these patented developments are what set Mercedes models apart from other cars, thus underlining their role as safety pioneers.
The following are examples of the intelligent and effective features that help make a Mercedes what it is:
  • Wheel support during offset front-end collision
    A forward extension to the side skirts supports the wheel in the event of an offset frontal crash, thus preventing it from penetrating the footwell. This set-up also enables more energy to be absorbed through the wheels.
  • Foam padding in the footwell on the driver's side
    In all new Mercedes models, the footrest, the footwell carpet and the area behind the gas pedal are all covered with energy-absorbing foam, which cushions any possible impact, thus reducing the danger to feet and legs.
  • Metal footwell panel for the passenger
    The footrest in the footwell on the front passenger side comprises a metal panel covered with energy-absorbing foam, which cushions the impact should the passenger's feet strike the footrest. In addition, the metal panel is designed to deform and thus absorb impact energy. When subject to particularly high loads, the lower mounting points of the footwell plate are designed to release.
  • Impact-absorbing elements in the interior pillar trim
    In the event of a side collision, the sturdy body structure and special impact-absorbing elements in the interior pillar trim and seats combine to create a kind of roll cage. This also ensures adequate space for proper inflation of the sidebags.
  • Wooden trim with splinter protection
    The wooden trim in the interior of the E-class is made up of multiple layers. Metallic strips mounted on the back of the trim prevent the wood from splintering in the event of a collision.
  • Automatic emergency cutoff for fuel system
    To reduce the risk of fire, the engine and fuel pump are switched off in accidents that exceed a certain severity. In addition, the injection valves are automatically opened in order to reduce the pressure in fuel lines. Certain portions of the fuel lines are also steel clad ("armored hoses").
  • Flashing brake lights
Accident research shows that three-quarters of all accidents could be avoided if drivers received clear advance warning of the impending danger. Mercedes-Benz has therefore developed the adaptive brake light. This can make a major contribution toward preventing head-to-tail collisions, because, as studies show, reaction times in emergency braking situations are shortened by up to 0.2 seconds when conventional brake lights are replaced by flashing red hazard lights. As a result, the braking distance of a car behind can be reduced by around 4.4 meters at a speed of 80 km/h and by as much as 5.5 meters at 100 km/h. In other words, flashing brake lights are an effective means of preventing head-to-tail collisions. Moreover, this technology also enhances safety for those on the roads not driving a Mercedes-Benz.
Mercedes experts initially tested various types of hazard lights. They discovered that brake lights that flash around four times as rapidly as conventional orange hazard lights are particularly effective in warning drivers of an emergency stop and therefore a possible head-to-tail collision. The Mercedes study also revealed that activating conventional hazard lights in dangerous situations had only a minor effect on drivers' reaction times.
Mercedes accident researchers at work: the Accident Research unit at Mercedes-Benz has been analysing and reconstructing traffi c accidents since 1969, the aim being to fi nd out more in order to further improve the safety of Mercedes models.
Mercedes accident researchers at work: the Accident Research unit at Mercedes-Benz has been analysing and reconstructing traffi c accidents since 1969, the aim being to fi nd out more in order to further improve the safety of Mercedes models.
Mercedes accident researchers at work: the Accident Research unit at Mercedes-Benz has been analysing and reconstructing traffi c accidents since 1969, the aim being to fi nd out more in order to further improve the safety of Mercedes models.
Mercedes accident researchers at work: the Accident Research unit at Mercedes-Benz has been analysing and reconstructing traffi c accidents since 1969, the aim being to fi nd out more in order to further improve the safety of Mercedes models.
Mercedes accident researchers at work: the Accident Research unit at Mercedes-Benz has been analysing and reconstructing traffi c accidents since 1969, the aim being to fi nd out more in order to further improve the safety of Mercedes models.
Mercedes accident researchers at work: the Accident Research unit at Mercedes-Benz has been analysing and reconstructing traffi c accidents since 1969, the aim being to fi nd out more in order to further improve the safety of Mercedes models.
Mercedes accident researchers at work: the Accident Research unit at Mercedes-Benz has been analysing and reconstructing traffi c accidents since 1969, the aim being to fi nd out more in order to further improve the safety of Mercedes models.