Vehicular Accident Reconstruction

Summary

Vehicle accident reconstruction is the forensic science of determining the factors contributing to individual motor vehicle accidents. By collecting, documenting, and analyzing evidence recovered from and relating to the scene of a motor vehicle accident, experts can reconstruct the event and determine the primary cause as well as any malfunction, negligence, or criminal intent attached to it. Typically performed in cases involving death or injury, this type of accident investigation applies knowledge from various sciences to discern the roles of drivers, vehicles, and the environment in the collision. Data analysis determines how and why a collision occurred and, in some cases, how similar collisions might be prevented.

Definition and Basic Principles

Vehicle accident reconstruction is the forensic science of determining the factors contributing to motor vehicle accidents. The collision of a moving vehicle, such as a car or truck, with another moving vehicle, stationary object, or pedestrian can often result in injury or death. Such an event warrants an investigation into the causative factors and analyses of the evidence are often woven into a reconstruction of the event for presentation in criminal and civil court cases. Physical evidence is collected at the scene, such as the wreckage of all vehicles involved and the scattered debris, alcohol containers, illicit drug paraphernalia, and possible distractions, such as cell phones. Photographs are taken of the environmental conditions of the scene, such as landscaping, snow, skid marks, road design, and traffic signs. Relative distances between points of interest are measured and recorded. Any witness statements are taken, and survivors are interviewed. The physical states of the drivers, any passengers, and any pedestrians are noted, including accident-related injuries and reaction impairment due to alcohol, drugs, or sleep deprivation. All of this information is analyzed in context to reconstruct the conditions that led to the collision and indicate its primary cause as well as any malfunction, negligence, or criminal intent attached to it.

Background and History

In 1959, the Insurance Institute for Highway Safety (IIHS), a nonprofit organization, was founded by three major insurance companies representing 80 percent of the American auto insurance market. Its purpose was to support highway safety research conducted by others to prevent motor vehicle collisions and to minimize injuries in the accidents that still occurred, thus saving lives and reducing financial burdens. Ten years later, IIHS became an independent research organization that studies human behaviors that contribute to collisions, vehicle design and integrity to protect occupants in collisions, and environmental conditions to eliminate obstacles and hazards.

Hugh H. Hurt Jr., a safety engineer, was the first to study motorcycle accidents. His research, initiated in 1976, was published in 1981 as "The Hurt Report," also titled "Motorcycle Accident Cause Factors and Identification of Countermeasures." His methods of data collection and the remarkable findings that came from keen analysis led to the emergence of the field of vehicle accident reconstruction.

National standardization for the field of vehicle accident reconstruction was first funded by the National Highway Traffic Safety Administration (NHTSA) in 1985. The resulting report was titled "Minimum Training Criteria for Police Traffic Accident Reconstructionists." One recommendation in the report was the formation of a certification board. In 1991, the Accreditation Commission for Traffic Accident Reconstruction (ACTAR) was incorporated to promote the recognition of minimum standards outlined in the NHTSA study within the scientific and legal communities.

How It Works

Investigators must approach each vehicle accident reconstruction as a realistic and unbiased narrative of scientific facts in context. Reconstruction involves three phases: investigation, in which evidence is collected; analysis, in which evidence is interpreted in context; and presentation, in which interpretations and conclusions are conveyed to persons who intend to use the information.

Investigation. In the investigation phase, evidence is collected in three areas: the vehicles involved in the collision, the environment in which the collision occurred, and the people involved in the collision. All vehicles are examined to determine the type of collision from the point of impact: head-on, rear-end, right-angle (also called T-bone), oblique (sideswiping), or rollover. Forensic mapping of all surfaces on each vehicle is performed to document the amount and location of damage. The direction of travel before and after the collision and the final resting position are noted for each of the involved vehicles and any collateral vehicles that evaded the collision. Information from event data recorders (EDRs) associated with the airbags is downloaded. Vehicles involved in the collision are thoroughly examined away from the scene. The weight of each vehicle and the engine capability are determined. Mechanical components, including the brakes, tires, and airbags, are analyzed for failure.

Evidence is collected from and about the scene of the collision. In addition to photographs, forensic mapping of the environment using electronic surveying equipment may be performed to produce a computer-generated scale diagram in either two or three dimensions. The precise location of the impact is identified. The length and location of tire marks are documented. The weather conditions, including temperature, visibility, and precipitation on the road surface, are noted. The road design, surface material, and the presence of significant imperfections are documented. The presence and location of traffic control devices are determined. Similarly, investigators document the presence and location of driver information, such as warning signs, signs of speed limit changes, and notice of other vehicles entering.

Evidence is also collected about the people involved in the collision. Blood samples may be taken to determine the physical condition of the drivers. Driver qualifications and experience are noted. Logbooks of commercial drivers are obtained. Photographs of impact injuries are taken. Statements are obtained from any witnesses to the collision as well as occupants of the vehicles and responding police officers. Video evidence from speed cameras or security cameras on nearby buildings is also obtained.

Analysis. Evidence is then analyzed to place information in the context of before, during, and after the collision. Measurements of tire marks, the degree of vehicle deformation, and the distance that the vehicles traveled after the collision are used to determine speed and the time of braking. The angle and speed of impact are calculated to determine the timing of the accident and any evasive maneuvers taken to avoid the collision. Two physical laws are considered: the conservation of energy and the conservation of linear momentum. The conservation of energy states that because energy can neither be created nor destroyed, it simply changes forms; in driving, the kinetic energy of motion is normally converted into heat from friction between the tires and the brakes and also the road. In a collision, kinetic energy is dissipated via a skid and the deformation of the vehicle and its occupants. The conservation of linear momentum relates the weights of the vehicles, the angle at which they collided, and the places where they came to rest. Momentum is the product of the vehicle's mass and velocity. Upon impact, the energy of momentum from one vehicle may be transferred to another vehicle, stationary object, or person. Thus, the colliding vehicles may be pushed off the road, a stationary object may be uprooted and displaced, and a pedestrian may become airborne, landing some distance away. One fundamental outcome of this analysis is determining the vehicles' speeds and relative positions at various points during the collision sequence.

To analyze the environmental evidence, investigators may use planar photogrammetry, a method that accurately measures three-dimensional objects in photographs and transforms points on multiple photographs to points in scale on a single, comprehensive two- or three-dimensional diagram. In addition, the characteristics of the road design, surface, and maintenance are analyzed to determine their effects on the momentum of the vehicle and the friction value for the dissipation of energy. One fundamental outcome of this analysis is to represent accurately the external conditions under which the collision occurred and the relative location of the collision in time and space. Of particular interest is the perspective of each driver before, during, and after the impact.

To analyze human behavior, blood samples are analyzed to determine alcohol or drug use or other medical conditions affecting a driver's reaction time. Logbooks are analyzed to determine whether a commercial driver was sleep-deprived. Impact injuries are examined to determine each occupant's position in the car, whether a seat belt was worn, and whether an airbag deployed. Evidence is examined to determine whether drivers accelerated, braked, or steered to avoid the accident. One fundamental outcome of this analysis is to calculate time-distance relationships and determine the point of perception for unimpaired and impaired drivers.

Presentation. The interpretations of evidence and the conclusions drawn regarding primary and contributory causes, criminal action, and civil liability may be presented in several forms. Written expert reports propose the most likely scenario of the collision to police and private clients and may include recommendations for preventing similar events. Oral trial testimony and depositions present educated opinions and hypotheses supported by evidence and science to attorneys, judges, and juries. Computer-generated scale diagrams provide easily understood visual information and animation produced from the time-distance correlations of the evidence. They can present evidence in real-time, so observers can appreciate the brevity of the driver reaction time and the length of time that the vehicles continued to travel after the collision. Animation can also present the same scenario from different vantage points, such as those seen by the drivers of the two vehicles.

Applications and Products

Vehicle accident reconstruction is performed in cases of collisions that result in injuries, deaths, and significant property damage. It may be performed to determine criminal action or negligence, including which, if any, traffic laws were violated. Forensic evidence may also indicate intentional action, such as homicide, suicide, deliberate property damage, or attempted police evasion. Collision reconstruction may also be performed to determine liability and financial responsibility, particularly in cases in which the parties involved dispute the circumstances of the accident and deny responsibility.

Collision reconstruction may be performed for various clients, including prosecuting attorneys, attorneys for both plaintiffs and defendants, insurance company claims adjusters, trucking companies and other fleets of commercial vehicles, manufacturers contemplating a product recall, and automobile manufacturers and consumer advocates trying to determine crash test ratings.

Collisions may involve single vehicles meeting barriers, such as guardrails, trees, overpasses, and walls. They may occur between multiple passenger or commercial vehicles. Vehicles may also collide with pedestrians, animals, and other vehicles, such as motorcycles, bicycles, golf carts, snowmobiles, all-terrain vehicles, construction equipment, farm equipment, and coupled trailers.

In determining mechanical failure, environmental hazards, and operator error, analysis is based on precise scientific formulas, accurate detailed measurements, and certain knowledge of the multiple and variable conditions present. Environmental measurements are taken with electronic survey equipment, such as a total station, which uses trigonometry and triangulation to determine absolute locations, elevations, and road camber. It measures distances, horizontal angles, and vertical angles. However, it must be planted upon a known point and have a clear line of sight to landmarks. Vehicle data may be processed by finite element analysis, a mathematical method used in the analysis of elasticity and structure in engineering. It is used in the design and development of vehicles to determine strength while minimizing weight and cost. It is also used to determine the distribution of stresses and displacements in a vehicle collision.

Anthropomorphic test devices, commonly called crash test dummies, come in various sizes corresponding to all genders from infants to adults in the fifth, fiftieth, and ninety-fifth percentile of the American population. They are used to determine how bodies are affected in a crash—what they hit within the interior of the vehicle, how they are ejected, and what injuries may result. The height, weight, and body measurements of the test dummies can be modified to model the actual participants in a specific accident. Injuries that commonly result from a vehicle accident are found in the spine, shoulder, and knee.

Conclusions learned from vehicle accident reconstruction may be applied to amusement ride safety, especially as roller coasters become more complex and exert greater stress on riders' bodies, including potential brain injuries. In addition, the impact testing of motorcycle helmets has shown that while a significant blow can reduce the protective capability of the helmet, even after ten more blows, a helmet still retains some capacity to protect the skull, suggesting that wearing a helmet that has already received a forceful impact is still better than not wearing a helmet.

Studies of accident reconstruction data have led to improvements in roof strength requirements to protect occupants in the event of a rollover. Fuel tank integrity requirements have also been upgraded to reduce the likelihood of impacted vehicles bursting into flames, possibly trapping the occupants. Along with airbags, energy-absorbing steering columns have become standard equipment to protect drivers in a collision by preserving the inside space around them. Advanced side-view mirrors and camera-assisted backup systems reduce blind spots, thus reducing the risk of collision. Additionally, technology, such as sensors and radar, have increasingly been incorporated in car models to allow for distance and potential collision warnings as well as automatic emergency braking systems.

Careers and Course Work

Vehicular accident reconstructionists typically come from one of two backgrounds: criminal justice or engineering. While the educational paths are different for these two fields, the specialized field of vehicular accident reconstruction has basic principles and methods and requires proficiency in the studies of mathematics, physics, forensic investigation, photography, computer-aided design (CAD) software, mechanical engineering, and human anatomy and physiology.

Police officers reconstruct collisions to determine if any criminal action contributed to the event. They investigate for evidence of speeding, mechanical violations (such as use of seat belts and headlights or faulty tires, windshield wipers, or brake lights), alcohol use, drug use, and hours-of-service violations, which may cause commercial truckers to become sleep-deprived. They earn a degree in criminal justice and then specialize in vehicle accident reconstruction by taking certification courses at accredited universities.

Independent vehicular accident investigators are typically hired to determine liability and financial responsibility. While they may be retired or off-duty police officers or automotive technologists, they are more commonly licensed professional engineers in the automotive, materials, mechanical, biomechanical, safety, or structural dynamics engineering fields. They first earn a Bachelor's degree in civil or mechanical engineering and then pursue Master's and Doctoral degrees to gain depth of specialized knowledge as well as credentials for acting as an expert witness in civil and criminal court cases. Such investigators may be hired by attorneys, insurance companies, corporations, or private individuals. Some choose to become professors and conduct research into subspecialties, such as tire marks, impact injuries, and motorcycle safety.

Social Context and Future Prospects

Vehicular accident reconstruction will remain an in-demand service as long as there are vehicular accidents, which will likely be as long as there are vehicles. While the essential nature of the job remains the same, the techniques and technology involved evolve as systems improve. Computer software is becoming increasingly sophisticated and plays an ever-increasing role. Digital photographs may be entered immediately into software programs for instantaneous measurements. Computer-aided modeling videos offer three-dimensional perspectives of vehicle accident reconstructions that are easily understood, especially by juries. Videos can demonstrate real-time conditions, such as how sight lines were obstructed as the vehicle traveled and how little time was available for drivers to react.

Vehicle safety equipment is also becoming more complex, often providing significant data for accident reconstruction. Airbag modules receive data from numerous sensors to determine if the airbag should be deployed; some store this information in an event data recorder (EDR). That data can be downloaded for reconstruction purposes, although it was initially intended to analyze airbag failures. These EDRs vary with the vehicle model in which they are installed; those in passenger vehicles generally demonstrate the vehicle deceleration pattern due to the collision. Others can record information from the five seconds preceding the accident, including vehicle speed, engine performance, brake light activation, and seat belt use.

Additionally, the ubiquity of smartphones and other devices with sophisticated sensor capabilities and internet connectivity offers further opportunities to collect evidence relevant to an accident. However, collecting and using such information raises questions about data privacy and fair use. Furthermore, more cars are equipped with advanced driver assistance systems in the twenty-first century, including lane departure warnings, adaptive cruise control, forward collision warnings, and active automatic braking systems. Reconstruction investigators thus have an even more significant amount of electronic data to analyze the collision and study the effectiveness and limitations of such technology in preventing collisions.

As the body of vehicle accident reconstruction experience grows, so do libraries of information on characteristics of vehicle materials, tires, driving surfaces, and visibility factors. The mass of data on causative factors continue to be used to make recommendations to improve transportation safety at both the manufacturing and legislative levels. Innovations in accident reconstruction also continue to be made. 3D imaging creates animated models of the accident scene, and drones capture aerial views. The software that recreates aspects of accidents is becoming more intuitive and advanced. Accident reconstruction also uses new technology from artificial intelligence to create algorithms from the data analysis of past accidents. Finally, the biomechanical analysis of injuries provides an even more in-depth event analysis. 

Bibliography

Brach, Raymond M., and R. Matthew Brach. Vehicle Accident Analysis and Reconstruction Methods. 3rd ed, SAE International, 2021.

Brown, John Fiske, Kenneth S. Obenski, and Thomas R. Osborn. Forensic Engineering Reconstruction of Accidents. Springfield, Ill.: Charles C. Thomas, 2002.

Flynn, Tom, and Mike Yang. "The Role of Driver-Assistance Technology in Accident Reconstruction." MEA Forensic, 4 Mar. 2020, www.meaforensic.com/advanced-driver-assist. Accessed 28 Mar. 2024.

Franck, Harold, and Darren Franck. Ethical Standards in Forensic Science. Boca Raton, Fla.: CRC Press, 2020.

Franck, Harold, and Darren Franck. Mathematical Methods for Accident Reconstruction: A Forensic Engineering Perspective. Boca Raton, Fla.: CRC Press, 2010.

"History of ACTAR." Accreditation Commission for Traffic Accident Reconstruction, 2018, actar.org/about/history. Accessed 28 Aug. 2018.

“How Technological Advancements are Reshaping Accident Reconstruction.” Evidence Solutions, www.evidencesolutions.com/accident-reconstruction-articles/how-technological-advancements-are-reshaping-accident-reconstruction. Accessed 28 May 2024.

Noon, Randall K. Forensic Engineering Investigation. Boca Raton, Fla.: CRC Press, 2001.

Rivers, R. W. Evidence in Traffic Crash Investigation and Reconstruction: Identification, Interpretation, and Analysis of Evidence and the Traffic Crash Investigation and Reconstruction Process. Springfield, Ill.: Charles C. Thomas, 2006.

Vangi, Dario, Filippo Begani, Florian Spitzhuttl, and Michelangelo-Santo Gulino. "Vehicle Accident Reconstruction by a Reduced Order Impact Model." Forensic Science International, vol. 298, 2019, pp. 426e1-426e11, DOI: 10.1016/j.forsciint.2019.02.042. Accessed 6 June 2022.

Van Kirk, Donald J. Vehicular Accident Investigation and Reconstruction. CRC Press, 2001.

“What Is Accident Reconstruction.” Austin Visuals, 26 Mar. 2024, austinvisuals.com/what-is-accident-reconstruction. Accessed 28 May 2024.