The Ins and Outs of Vehicular Accident Reconstruction, From the Experts Point of View

TASA ID: 417

In vehicular accident reconstruction, it is always a concern when attorneys wait until the eleventh hour to call in an engineering expert to first analyze a case. The accident reconstructionist will do his best work when there is ample time to visit the site as soon as possible in order to take measurements, observe the evidence, and analyze the case. If the expert cannot visit the scene soon after the event, good, clear and detailed photographs are critical. Photographs will enable the expert engineer to use photogrammetry to determine measurements of the damage and observe any photographed debris on the roadway.

The use of computer accident reconstruction software, or Simulation Model of Automobile Collisions (SMAC), such as McHenry, PC-Crash, or Visual Statement Software, among others, aids in the analysis of the event. Each of the software programs requires that the specifications of the vehicles involved, such as weights and dimensions, be known. The programs allow for the input of steering and braking information and the times for such activity by the drivers, as well as the various surfaces traveled on.

The SMAC programs are time-dominated mathematical models in which the vehicles are represented by differential equations derived from Newtonian mechanics, combined with empirical relationships for some components, such as crush properties and tires. These are solved in successive time increments by digital integration. The SMAC computer model is an open form of reconstruction, wherein the user specifies the dimensional, inertial, crush and tire properties of the vehicles, the initial speeds, angles and driver control inputs. The program produces detailed time-histories of the vehicle trajectories, including the collision responses. The user compares the SMAC predicted trajectories and collision deformations with the physical evidence to determine the degree of correlation. Iterative runs are performed, varying initial speeds, heading angles and control inputs, until an acceptable match of the physical evidence is obtained.

Crash data can be estimated based on NHTSA (National Highway Traffic Safety Administration) crash tests for various tested vehicles. This allows for the hardness/softness of the vehicle crush, which will relate to the amount of g's (deceleration) and delta-V (change in velocity) that the vehicles will encounter during impact, which in turn can relate to the occupant injury.

Sketches drawn in CAD programs can be imported into software to illustrate where the vehicles impacted and where their rest positions are located. Obstacles can be inserted to reveal how a vehicle behaves when it strikes an obstacle other than another vehicle.

Damage profiles of the vehicles are created so that comparisons can be made between the photographs of the crushed vehicles and the damage profiles. The rest positions of the vehicles are important because the computer programs allow the vehicles to come to rest after impact. The closer the simulation allows the vehicles to come to rest, as depicted in police report measurements or photographs, the more accurate the simulation of the event in terms of vehicle speed and post-impact motion.

The development and use of computer-based accident reconstruction programs have provided the ability to view images so that the events that led up to the crash can be easily understood.

This article discusses issues of general interest and does not give any specific legal or business advice pertaining to any specific circumstances.  Before acting upon any of its information, you should obtain appropriate advice from a lawyer or other qualified professional.

This article may not be duplicated, altered, distributed, saved, incorporated into another document or website, or otherwise modified without the permission of TASA.

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