Vehicular accident reconstruction
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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 and reconstruction to identify the collision causation and contributing factors in different types of collisions, including 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 analysis and may make use of software to calculate useful quantities. The accident reconstruction provides rigorous analysis that an expert witnesses 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.
The National Highway Traffic Safety Administration funded the first national guidelines for the standardization training in the field of traffic accident reconstruction in 1985. This led to the establishment of Accreditation Commission for Traffic Accident Reconstruction (ACTAR), an industry accreditation group. This field of motorcycle accident research was pioneered by Hugh H. Hurt Jr. His meticulous accident reconstructions of motorcycle accidents helped to explain that proper helmets reduced head injuries, most motorcyclists needed more driver training to control skids, and a large percertage of motorcycle accidents involved left-turning automobiles turning in front of the oncoming motorcycle.
Scene inspections and data recovery involves 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 of the collision, measurements of the scene, eyewitness testimony, and legal depositions. Additional factors include steering angles, braking, use of lights, turn signals, speed, acceleration, engine rpm, cruise control, and anti-lock brakes. Witnesses are interviewed during accident reconstruction, and physical evidence such as tire marks are examined. The length of a skid mark can often allow calculation of the original speed of a vehicle for example. Vehicle speeds are frequently underestimated by a driver, so an independent estimate of speed is often essential in accidents. 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 such as speed of the vehicle a few seconds for a collision.
Vehicular accident reconstruction analysis includes processing data collecting, 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 and crime scenes and to perform other useful tasks involved in reconstructing collisions. Accident reconstruction software is regularly used by law enforcement personnel and consultants to analyze a collision and to demonstrate what occurred in an accident. Examples of types of software used by accident reconstructionists are 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 a knowledge of physics, dynamics and engineering. When animations are used in a courtroom setting, they should be carefully scrutinized. Animation software can be easily misused, because motions which are not physically possible can be displayed. A reliable animation must be based on physical evidence and calculations which 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.
Motorcycle Accident Reconstruction
Motorcycle accident reconstruction is similar to other accident reconstruction techniques and relies on the same basic principles of conservation of energy and momentum as automobile accident reconstruction plus adds the specifics of motorcycle dynamics and rider control. Proper reconstruction of a motorcycle accident requires detailed knowledge of motorcycle dynamics plus knowledge of how motorcycles react to rider input.
Motorcycle accident reconstruction follows reverse a chronological order of events, working from the point of rest of the motorcycle and/or rider backwards to a point in time before to the start of the accident sequence to when possible actions could have prevented the crash.
Motorycle accident reconstruction relies on knowledge of the 5 phases of a motorcycle accident.
Perception-Reaction: This is the phase where the rider perceives a hazard in front of him 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 rider typically engages in some type of avoidance using steering or braking using the front brake, rear brake or a combination. Physical evidence at the scene combined with statements from witnesses can give clues as to what type of avoidance occurred.
Pre-impact Sliding: During braking, riders may overuse the motorcycle brakes, resulting in locking the front and/or rear wheel. If the front wheel locks, the rider will almost certainly lose control and crash. If the rider loses control and crashes while braking, the motorcycle and rider usually separate and slide in the same trajectory they were moving in before the crash.
Impact: The bike and/or rider may collide with other object like a vehicle or guardrail. Damage caused by impact can be evaluated and combined with sliding distance to help determine the motorcycle’s speed during the accident sequence.
Post-impact Motion: After impact, additional movement to the point of final rest can occur. The rider frequently separates from the motorcycle and travels independently to the final point of rest. Analysis of post-impact travel distance can also determine speeds associated with the accident. 
- The History of ACTAR, Retrieved on Feb. 22, 2010.
- Hugh Hurt Jr., Engineer Who Studied Motorcycle Accidents, Dies at 81, Martin, Douglas, The New York Times, 2009-12-03. Retrieved on Feb. 23, 2010.
- "The Ferrari That Split in Half". Slate.com. 2006-04-18. Retrieved 2010-02-24.
- Forensic animator recreates crimes in 3-D and video, Thompson, Jr., Dennis, The Statesman Journal, 2010-02-22. Retrieved on Feb. 22, 2010 [dead link].
- Taoka, George (March 1989). "Brake Reaction Times of Unalerted Drivers". ITE Journal 59 (3): 19–21.
- Motorcycle Accident Reconstruction Techniques, Kittel, Mark, P.E. 2012-06-11.
- Fatal Accident Reconstruction Team
- Forensic animation
- Forensic engineering
- Human factors
- Skid marks
- Total stopping distance
- Accreditation Commission for Traffic Accident Reconstruction (ACTAR)
- National Highway Traffic Safety Administration
- National Academy of Forensic Engineers