This article provides an introduction to heavy truck crash reconstruction, including an explanation of why the Conservation of Energy (COE) method is crucial for accurate and reliable reconstructions.
In reconstructing vehicle crashes involving heavy trucks, several important factors must be considered. These issues may be less relevant in automobile to automobile crashes.
Size: Trucks are bigger and heavier than automobiles, up to 40 tons, compared to 1-2 tons. As the difference in mass between colliding vehicles increases, some calculation models may become less reliable.
Configuration: There are many different configurations of heavy trucks, from a single unit straight truck to 3 trailer triples. Trailer types and payload conditions of these truck configurations affect vehicle maneuvering and stopping characteristics.
Damage: Damage to the truck in a truck-automobile crash is usually minimal compared to the auto. This may require alternate approaches to calculating forces.
Most automobile crash reconstructions are performed using the Conservation of Momentum (COM) method. This method is acceptable and appropriate for collisions involving vehicles of similar mass; however, as the difference in mass between the colliding vehicles grows (such as heavy truck-automobile collisions), the COM method becomes increasingly sensitive to uncertainties in impact and departure angles. Using the Conservation of Energy (COE) method may be more reliable in heavy truck-automobile crashes as it does not depend on the angles of impact and departure.
Energy calculations require a quantification of the total energy dissipated in the crush of the vehicles and any post impact travel. Energy being conserved means the total energy after the collision is equal to the total energy prior to the collision. There is usually little damage done to the heavy components of the truck; the plastic bumper and hood may be damaged, but the energy used for this is relatively low. The energy to crush the automobile can be calculated accurately by measuring crush on the passenger/light truck or SUV vehicle. Most energy formulas for automobiles are developed from crash tests run at or below 35 mph into a solid barrier. Barrier tests commonly provide an acceptable model for measuring automobile crush against a heavy truck.
Once the crash speed is established, the vehicle movements before the crash should be analyzed to establish pre-crash speeds. The calculations for the auto are no different than in an auto to auto crash, but a heavy truck brings more issues that need to be investigated to calculate a proper brake factor for the truck.
Skid marks are often used to estimate critical speeds and deceleration rates, but with 5 or more axles on a heavy truck determining what type of tire mark and what axle made the tire marks, it is more complicated.
In order to provide a reliable analysis, an expert should have training, education, and experience in physics as well as heavy truck dynamics/systems to understand the forces and energy involved and accurately reconcile those forces with the crashed vehicles.
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