Vehicle Damage Correlation to Injury Severity
A recent NHTSA report shows that crash characteristics become more favorable for the occupant as the amount of residual deformation increases. This excludes crush intrusion into the occupant compartment. Robbins concluded that in crashes where there is no intrusion into the occupant compartment, “A common misconception formulated is that the amount of vehicle crash damage due to a collision, offers a direct correlation to the degree of occupant injury.” This author further emphasized that the concept of determining injury risk based from crush depth only is false reasoning. Although crush depth can be used for determining delta-Vs and PDOFs, other variables also must be considered before injury severity can be determined accurately. Many automobile insurance companies promote the myth that collision injuries correlate to the vehicle external structural damage and costs of repair, and have taken this position as a matter of policy. A claims adjuster might reject a claim, concluding that since there was only $1,000 worth of damage to the vehicle on a repair estimate, the person could not possibly be hurt, and not authorize any payment for treatment. On the other hand, the same adjuster might assume that since the car was totaled, the occupant must have significant injury, and authorize payment without any dispute. The assumption that the risk of injuries related to the amount of external vehicle damage in all types of crashes has little scientific basis.
In a recent NHTSA report, Romilly et al. stated, “The mechanics of a high speed collision are relatively well documented. The vehicle structure deforms, converting the system’s kinetic energy into sound, thermal, and strain energies. The rate of deformation is a result of the vehicle’s stiffness characteristics while the amount of recoverable deformation is a function of its elastic properties. At high impact speeds, very little elastic recovery occurs and the vehicle generally behaves as a plastic body. At low impact speeds, however, plastic behavior may be absent allowing most of the total impact injury to be recovered in elastic rebound. For the occupant, the best ride down profile occurs when the vehicle behaves as a plastic body with large deformations to reduce the overall acceleration. This creates a major dilemma for the manufacturer, occupant, and insurer. Each would like the vehicle to provide the maximum protection for the occupant with the minimum material damage to the vehicle during a collision. As the vehicle becomes stiffer, the vehicle damage costs are reduced as less permanent deformation takes place. However, the occupant experiences a more violent ride-down, which increases the potential for injury. This implies that vehicles that do not sustain permanent damage in low speed impacts produce correspondingly higher dynamic loadings on their occupants than those that deform plastically under the same or possibly more severe impact conditions