The Nuts and Bolts of Accident Reconstruction

CHICAGO (Oct. 4, 2005) - Accident Reconstruction (AR) is a lot like automobile service and repair. It requires a braiding of art, science, experience and professional ethics to get the job done right. And similar to the evolution of professional technicians and shop management, AR also has undergone changes in technology - some imposed upon it, some developed from within, some accepted as God-sends and others resisted when seen as being too controversial. 

One of those technological innovations is the Event Data Recorder (EDR), more commonly known as a black box. While there are a number of ethical, legal and other concerns regarding their use, EDRs have transformed the landscape of accident reconstruction and specifically changed the recipe for reviewing and reconstructing accidents.

In accident reconstruction, there is an analysis methodology known as the Haddox Matrix, shown in Figure 1. The Haddox Matrix breaks down the analysis of a crash into three major elements - human, vehicle and environmental - at three different points in the accident - precrash, crash and post-crash. Essentially, the table identifies nine primary evidence boxes that, if and when accurate data can be uncovered, enables a reasoned, full and accurate accident reconstruction to be done. 

Prior to the modern technology's influence, the means to measure and assess accident related data was very limited. According to experts in the field, such as Harris Technical Services, even with adequate experience and methodology, often what resulted in at best, was a well-considered "expert opinion." 

Prior to the use of EDRs, investigators could determine and record information only in some of the nine evidence boxes. There were boxes for which no evidence could be mined reliably, as indicated by the question marks. These information gaps, much like a customer who withholds some relevant information from a technician, could be key in diagnosing what had occurred before moving forwards.

For instance, some of the human and environmental elements could be surmised post-crash, but not before or during. In regards to the vehicular element, information was more limited than what can be conveyed by modern sensors and tools. Analysis of skid marks, calculation of delta-V (velocity change) and collision damage was close to the extent of what an investigator could determine in these areas. Even then, accuracy was in doubt.

The rest of the needed information, if it was even available, was anecdotal and subjective in nature. Examples included eyewitness statements or even information provided by third parties not present (e.g. general weather reports for the vicinity of the crash as opposed to specific conditions at the crash site at the time of the incident). Bottom line? There was simply no way to know for certain if the expert's considered conjecture was what actually occurred, especially if and when the data was based more on subjective rather than objective input. Consequently, the findings rendered by investigators could vary with not only with experience and training, but their individual judgment as well. 

And those expert opinions, whether accurate or not, could impact the lives of people - survivors, family members, defendants and others.

Many individuals and organizations, such as the National Transportation Safety Board (NTSB), the National Highway Transportation Safety Administration (NHTSA), some automakers and parts manufacturers, AR specialists and insurers, saw potential in the use of EDRs as a means to next-generation safety and the collection of accurate accident data.

In late 2004, after years of information gathering, studies and research, the NTSB recommended that black boxes be mandated. Shortly thereafter, NHTSA published a rule in the Federal Register calling for the following: 

* Require that the EDRs voluntarily installed in light vehicles record a minimum set of specified data elements useful for crash investigations, analysis of the performance of safety equipment (e.g. advanced restraint systems) and automatic collision notification systems (ACNs).

* Specify requirements for data format.

* Increase the survivability of the EDRs and their data by requiring that the units function during and after the front, side and rear vehicle crash tests specified in several federal motor vehicle safety standards.

* Require vehicle manufacturers to make publicly available information that would enable crash investigators to retrieve data from the EDR.

* Require vehicle manufacturers to include a brief standardized statement in the owner's manual indicating that the vehicle is equipped with an EDR and describing the purposes of EDRs. 

NHTSA recognized that EDRs were able to provide the missing links in crash events reliably, accurately and objectively. As well, the Agency was aware that while most automakers were installing some sort of EDR in vehicles already, the rule provided encouragement and motivation to those automakers not doing so. Using EDRs in the vehicles that most Americans drive personally would complement the use of black boxes elsewhere in planes, trains, buses and commercial trucks to enable a better understanding of accidents - both in causes and solutions to improve safety for all.

Vehicle airbag EDRs are less sophisticated than those used in trains and planes. They spring into action when an airbag is deployed in the event of a crash. EDRs provide standardized information that is stored onto a microchip inside the black box for a five-second period before the impact. According to Harris Technical Services, the stored information includes vehicle speed, throttle position, engine speed and brake switch activation. EDRs also can monitor and store other pieces of information, including crash pulse, seat belt usage, airbag deployment time and location. 

Storing relevant information within an EDR is just one side of the equation. But it still has to be retrieved.

From the earliest use of EDRs, Vetronix says it worked with automakers such as General Motors and Ford Motor Co., as well as national government agencies like NHTSA and NSTB. In addition, the company has cooperated with certification and standard organizations such as the Society of Automotive Engineers (SAE) and the Institute of Electrical and Electronics Engineers (IEEE), as well as researchers and other interested parties.

As illustrated in the data retrieval system diagram, the system consists of a laptop computer with proprietary software, a CDR interface module and specially designed vehicle interface cables that couple to the EDRs. CDR systems enable an AR specialist to retrieve relevant and useful scientific data before and through to the point of the accident. This information, when collated with other traditional field investigation evidence, results in a more comprehensive report.

The CDR system can retrieve the following data, for five seconds before impact: vehicle speed, engine speed, throttle status and brake status; the on/off status of seatbelts, airbags and SIR warning lamp; time to airbag deployment; ignition cycle count at event time and investigation time; maximum delta-V for a non-deployment of airbags event; delta-V time for a frontal airbag deployment event; and the time from vehicle impact to time of maximum delta-V, crash pulse, which measures the severity and duration of impact; and the time between airbag non-deployment and deployment event if within five seconds of impact.

Information obtained from vehicle black boxes by the CDR is presented both in graph and printed form. As illustrated in Figure 5, the basic metrics are displayed on a graph for the five second period immediately preceding and at impact - in this case vehicle speed, engine speed, throttle position and brake switch status. For accident reconstruction investigators, this data answers such questions as how fast the vehicle was going, was it accelerating or slowing, if/when brakes were applied and the severity and duration of the crash impact. An alternate video view of the information can be seen at Harris Technical Services' Web site at www.harristechnical.com/cdr80.htm.

Some have criticized the reliability and accuracy of black boxes. NHTSA notes that credible organizations have developed standards that are accepted within the industry. SAE has published data retrieval guidelines, and the IEEE has developed standards for EDRs (IEEE1616 ISBN: 0-7381-4499-1). NHTSA also has established through broad vehicle crash testing that data collected from EDRs by CDR systems have a much more scientific and objective nature, are more consistent and have a known and narrower degree of error compared to traditional field investigative techniques. When incorporated into accident reconstruction reports, based on all the evidence reviewed, a more complete understanding is made possible. 

In an age of ever more complicated vehicles and integrated systems, few technicians today would rely solely on their experience and best guess in determining what was ailing a vehicle; they use the diagnostic tools now available. So, too, with AR, wherein investigators use tools such as a CDR to assist in their gathering of reliable evidence regarding an accident

In a letter to NHTSA, Dr. Ricardo Martinez, president of Safety Intelligence Systems Corp. and a former NHTSA administrator, had expressed concern about relying on only traditional field investigation in accident reconstruction: "There is a significant difference - sometimes more than 100 percent - between derived [field] crash severity calculations and those directly measured by a vehicle. A measurement is worth a thousand opinions." 

Joseph E. Badger, an accident reconstruction consultant with Harris Technical Services insists that proper training and experience is vital to ensuring a sound accident reconstruction results. Being qualified to conduct an AR is not a function of training only. This applies not only in the use of CDR system tools but in the traditional field methods as well. 

He cites concerns about some police academies that allocate between two hours to five days for accident investigation. "Even a five-day course - nay, not even a five-week course - makes a qualified accident reconstructionist. Neither does a five-year physics or engineering course. It not only takes training in the mathematics and engineering principles involved, but also years of practical hands-on, in-the-field experience," Badger says, "We find that some officers, including those who have had no more than a couple of weeks of reconstruction instruction, are holding themselves out as accident reconstruction experts, yet make grievous blunders. Sometimes without even realizing it." 

Investigators also require a good understanding of the relationships of accident factors, circumstances and modifiers, and sufficient data, before an accident can be analyzed, causation determined and the conclusions effectively presented. For instance, being intoxicated may simply be a factor in an accident, but not a cause of an accident - such as if a drunk driver had legally halted at a stop sign, was then rear-ended, with both drivers dying and no witnesses to the event present.

Besides cause-and-effect errors, Badger has seen mistakes in traditional field investigation of physical, as opposed to EDR, evidence. Errors in speed calculations, misinterpretations of yaw, flips and skid tests, inexact science such as rounding errors, misleading photographs of the accident scene and lack of thoroughness are just some of the mistakes he has observed. Competence is a choice.

Martinez provided an example of this concern in his letter to NHTSA. With the shift in automobile technology from mechanical to electrical systems and sensors, reliable physical evidence of the crash is diminishing. He shared how modern antilock brakes reduce skid marks, resulting in the old calculation methods understating some traditional field determinations about wheel and vehicle behavior. Errors in miscalculations of this type could incorrectly shape the consideration and final judgment of a court. 

Badger also expressed the concern that when EDR evidence is to be considered for admission by judges or later considered by jurors, a number of inherent problems can manifest themselves. First, an understanding of traditional field investigation without EDRs is lacking, as is an awareness of the types of errors that Martinez alluded to above. Secondly, they are also unlikely to understand the nuances of how the modern EDRs work. It is important to seek adequate education so that conclusions and decisions that are made are based on sound understanding.

It is also clear that human investigation and EDR data storage both have degrees of error. What has been established over time is that the margin of error using modern CDR tools is less than those that occurred without them and that more objective scientific data is made possible by employing EDRs. There are numerous court cases on record wherein the EDR data and human-reported data differed, if not being in outright conflict. Badger and those like him argue that ethical reconstructionists will ensure that discrepancies between technical and physical evidence that are known to them, are included in the report submitted to authorities. In addition, when evidence conveyed in an AR report is being considered, the known margins of error should be applied in that consideration to ensure all decisions fall within the bounds of reasonable doubt.

Badger emphasizes that accident reconstruction investigators must be beyond reproach in their methodology. "Before you hold yourself out as an accident reconstructionist, be sure you can back up your methodology. Such support is not simply saying you read it someplace or some teacher told you," he says.

Truth can be elusive. An accident is much like a jigsaw puzzle, with all the pieces hidden to begin with. While traditional field investigation methods can turn some of those pieces over, too many gaps are left to put the puzzle together. The advent of EDR devices and CDR tools enable the rest of the pieces to be seen. But ultimately it is the element of experience - the blend of training, hands-on thoroughness, patience and ethics - that determines whether the whole picture is put together in a way that not only makes sense, but also is accurate and defensible.

(Sources: Vetronix, Harris Technical Services, NHTSA, NTSB, SEMA)