Vehicular accident reconstruction is the scientific process of investigating, analyzing, and drawing conclusions about the causes and events during a vehicle collision. Reconstructionists are employed to conduct in-depth collision analysis to identify the cause of different types of collisions. This includes the role of the driver(s), vehicle(s), roadway and the environment. The laws of physics and engineering principles such as the conservation of linear momentum, work-energy methods, and kinematics are the basis for these analyses and may make use of software to aid in this task.
The accident reconstruction provides rigorous analysis that an expert witness can present at trial. Accident reconstructions are done in cases involving fatalities, and often when personal injury is involved. Results from accident reconstructions are also useful in developing recommendations for making roads and highways safer, as well as improving safety aspects of motor vehicle designs. These reconstructions are often conducted by forensic engineers, specialized units in law enforcement agencies, or private consultants.
Scene inspections and data recovery involve visiting the scene of the accident and investigating all of the vehicles involved in the collision. Investigations involve collecting evidence such as scene photographs, video and measurements of the scene, eyewitness testimony, and legal depositions. Witnesses are interviewed during accident reconstruction, and physical evidence such as tire marks and gouge marks are examined. The length of a skid mark and the location of gouge marks can often allow the location and speed of a vehicle to be determined. Inspection of the road surface is also vital, especially when traction has been lost due to black ice, diesel fuel contamination or obstacles such as road debris. Data from an event data recorder also provides valuable information.
All new vehicles are equipped with an onboard “Crash Data Recorder” or “Event Data Recorder” (CDR or EDR), commonly referred to as a “black box.” There are commercially available tools that will download the data contained on the black box. Information contained on the black box may include pre-crash data such as vehicle speed, brake status, throttle position, ignition cycles, seat belt status and others. The black box also records conditions at the time of the collision such as impact velocities and the timing of airbag deployment.
Accident reconstruction analysis includes processing data collected, evaluating possible hypotheses, creating models, recreating accidents, testing, and utilizing software simulations. Like many other technical activities, accident reconstruction has been revolutionized by the use of powerful, inexpensive computers and specialty software. Various types of accident reconstruction software are used to recreate crash scenes and to perform other useful tasks involved in reconstructing collisions. Accident reconstruction software is regularly used by law enforcement personnel and consultants to map vehicle damage profiles and debris fields in 3-D. It can also be used to analyze collisions, and to simulate what occurred in an accident. Examples of types of software used by accident reconstructionists are total station mapping, CAD (computer aided design) programs, vehicle specification databases, momentum and energy analysis programs, collision simulators, and photogrammetry software.
After the analysis is completed, forensic engineers compile report findings, diagrams, and animations to form their expert testimony and conclusions relating to the accident. Forensic animation typically depicts all or part of an accident sequence in a video format so that non-technical parties, such as juries, can easily understand the expert’s opinions regarding that event. To be physically realistic, an animation needs to be created by someone with knowledge of physics, dynamics and engineering. A reliable animation must be based on physical evidence and calculations that embody the laws of physics, and the animation should only be used to demonstrate in a visual fashion the underlying calculations made by the expert analyzing the case.
Accident reconstruction follows a reverse chronological order of events, working from the point of rest of the vehicle backward to a point in time before the start of the accident sequence to help determine information such as vehicle speeds and positions before the crash sequence began.
Some important phases involved in an accident reconstruction are Perception-Reaction time, Avoidance-Braking/Steering, Impact, and Post-Impaction Motion. These phases will be explained below:
• Perception-Reaction: This is the phase where the driver perceives a hazard and decides on a response. Perception-reaction time is estimated at 1.1 to 1.5 seconds.
• Avoidance – Braking/Steering: In this next phase, the driver typically engages in some type of avoidance using steering, braking or a combination of both. Physical evidence, such as skid marks and yaw marks, combined with statements from witnesses can give clues as to what type of maneuver occurred.
• Impact: The vehicle may collide with another object like a vehicle or guardrail. Damage caused by impact can be evaluated and combined with deceleration rates to help determine the vehicle’s speed during the accident sequence.
• Post-impact Motion: After impact, additional movement to the point of final rest can occur. Analysis of post-impact travel distance can also help determine speeds associated with the accident.
Accident reconstruction is a valuable tool in explaining to juries how an accident happened and what could have been done to avoid the accident or mitigate the injuries. We are very fortunate to work with some of the top accident reconstructionists in the world. These experts are a valuable asset to us and for our clients. If you need more information on this subject, contact Graham Esdale, a lawyer in our firm who handles product liability litigation, at 800-898-2034 or by email at Graham.Esdale@beasleyallen.com.
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