Traffic collision reconstruction is the process of investigating, analyzing, and drawing conclusions about the causes and events during a vehicle collision. Reconstructionists conduct collision analysis and reconstruction to identify the cause of a collision and contributing factors including the role of the driver(s), vehicle(s), roadway and general environment. Physics and engineering principles are the basis for these analyses and may involve the use of software for calculations and simulations. Collision reconstruction is sometimes used as the basis of expert witness testimony at trials. Collision reconstructions are performed in cases involving fatalities or personal injury. Results from collision reconstructions are also sometimes used for making roads and highways safer, as well as improving safety aspects of motor vehicle designs. Reconstructions are typically conducted by forensic engineers, specialized units in law enforcement agencies, or private consultants.
History Crash analysis dates back to shortly after the first car crashed. The field got more analytical in the 1930s and in 1940 there was the first judicial opinion accepting the analysis of speed through measuring skid length and using that information with the principle of Conservation of Energy. NY State City Magistrate Horn, 20 N.Y.S. (92nd) 149 (1940) 174 N.Y. Misc 235. The National Highway Traffic Safety Administration funded the first national guidelines for the standardization training in the field of traffic collision reconstruction in 1985. This led to the establishment of "Accreditation Commission for Traffic Accident Reconstruction" (ACTAR), an industry accreditation group. The field of motorcycle collision research was pioneered by Hugh H. Hurt Jr. His reconstructions of motorcycle collisions helped to explain that proper helmets reduced head injuries, most motorcyclists needed more driver training to control skids, and a large percentage of motorcycle collisions involved left-turning automobiles turning in front of the oncoming motorcycle.
Investigation Scene inspections and data recovery involves visiting the scene of the collision 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 collision 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 collisions. 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 the speed of the vehicle a few seconds before the collision. As part of the investigation of a vehicle collision, an investigator typically documents evidence at the collision site and the damage to the vehicles. The use of 3-dimensional laser scanning has become a common method for documentation. The product of scanning is a 3D point cloud that can be used to take measurements and create computer models used in the analysis of the collision. The 3D data can be incorporated into many of the computer simulation programs used in collision reconstruction. The 3D point clouds and models can also be used for creating visuals to illustrate the analysis and to show views of witnesses and the involved drivers.
Technology and data sources Modern collision reconstruction relies on data from a variety of electronic sources within vehicles. While physical evidence remains important, this digital data provides an objective record of a vehicle's behavior before, during, and after a collision.
Event data recorders (EDRs) Many modern vehicles are equipped with an event data recorder (EDR), often referred to as a "black box." The primary purpose of an EDR is to record and save data for a few seconds immediately before, during, and after a crash is detected. Investigators can use a commercially available tool, such as the Bosch CDR-Tool, to download this data. The report typically includes pre-crash parameters such as vehicle speed, brake status (ON/OFF), throttle position, seat belt status, and steering wheel angle. Some manufacturers, like Tesla, provide their own proprietary EDR retrieval tools.
Modern telematics and fleet data In addition to post-crash EDR data, reconstructionists increasingly use data from real-time telematics systems, which has created a dedicated market for crash reconstruction with telematics. A telematic control unit or an aftermarket GPS tracking unit provides a continuous log of a vehicle's activity. While standard systems may log data every second, some advanced aftermarket devices can record high-resolution telemetry data, including accelerometer readings, at intervals as frequent as milliseconds. This granular data, sometimes called a crash trace, allows for a detailed "slow-motion" reconstruction of a vehicle's movements immediately before and during an impact.
Video evidence Video footage provides a visual record of a collision. The use of video as a data source has become widespread with the adoption of dashcams.
Dashcams: Both consumer and commercial vehicles are often equipped with forward-facing cameras that record the events of a journey. Video telematics: In commercial fleets, video telematics systems use AI to automatically identify and upload video clips of harsh events (like a collision) to the cloud. This preserves the evidence and provides an objective view of the incident, which can be used to supplement the data from the EDR and the telematics system for a more complete reconstruction.
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