Accident Reconstruction

The fundamental objective of accident reconstruction is to determine what happened at one of several points in time.

The reconstruction of accidents is scientific work under established practical conditions. An accident case requires intensive thinking with respect to solution formulation, mathematical models, and required data input.

The five specific objectives of Accident Reconstruction are:

• Collision Analysis
• Injury Analysis
• Accident Avoidance Analysis
• Injury Avoidance Analysis
• Accident Causation Ranking

Collision Analysis:

In the collision analysis, all significant parameters of the crash itself are determined. In particular, vehicle speeds and travel directions immediately before and after the impact are computed. After-impact vehicle motion are analyzed and matched against existing scene data. Factors include points of impact relative to the roadway, impact configuration of the vehicles, crush damage analysis, vehicle rotation, occupant dynamics, accident scene markings, occupant ejection portals, and others.

In most cases, except for simple accident reconstructions, impact speeds are computed by use of computer programs to ensure mathematical accuracy.

Injury Analysis

In the injury analysis all human and physical factors that might define and describe how the injuries were produced are analyzed. The analysis can include collision speed, occupant dynamics, kinematics, injury data and vehicle damages. Included are the occupant motion and contact relative to the vehicle interior, occupant-to-vehicle damage, vehicle interior design, safety devices (such as seat belts, airbags, head restraints, and padding), occupant seating, human tolerances to impact forces and deflections, and occupant injury data evaluation.

Accident Avoidance Analysis

With the overall accident circumstances established, such as pre-impact and impact speeds, as well as distance prior to impact, the accident avoidance analysis is conducted to determine if and how the accident could have been avoided or made less severe. Included in the accident avoidance analysis are vehicle motion computations or tests that show how a driver could have avoided the crash by braking, steering, or accelerating. Driver reactions are analyzed in the terms of view obstructions, night visibility, and appropriateness of driver response. In particular, the accident re-constructionist determines the maximum speed from which the vehicle could have stopped at the point of impact through braking, or arrived sufficiently later so that the other vehicle or pedestrian can clear the impact area.

The mechanical condition of the vehicle in terms of design, maintenance, or alterations are analyzed relative to its ability to respond safely to driver control inputs.

The roadway condition and traffic contribution to accident causation and hence potential for accident avoidance is analyzed in terms of basic roadway design, maintenance, sign, and control devices.

Injury Avoidance Analysis

In the injury avoidance analysis all factors involved of mitigating or avoiding bodily injuries are determined. Included are the study of medical data; effectiveness and use of seat belt, head restraint, airbag, and child restraint; interior vehicle design, dash geometry, steering wheel, padding, handles, knobs, and vehicle structure.

Accident Causation Ranking

In the causation analysis, all accident causation factors are studied based upon reasonable probability considering driver, vehicle, road, and environment.

Investigative Methodology

NFPA 921 Guide for Fire & Explosion Investigations, is designed to produce a systematic, working framework or outline by which effective fire investigation and origin and cause analysis can be accomplished. It contains specific procedures to assist in the investigation of fires and explosions. These procedures represent the consensus judgment of the committee on a system that, if followed, can be expected to lead to sound conclusions with supporting evidence. Deviations from these procedures, however, are not necessarily wrong or inferior but need to be justified.

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Risk factors related to fire are often interlaced. These include a fire’s source and magnitude, an occupant’s ability to escape from a burning vehicle, the time needed to escape, the location and type of emergency exits, and the flammability of the interior materials.

S4.2

Flammability of Interior Materials: When tested in accordance with S5, materials described in S4.1 and S4.2 shall not burn, nor transmit a flame front across its surface, at a rate of more than 4 inches per minute.

This test is normally done as a horizontal burn test rather than the more realistic burn test.