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A theoretical, mathematical, risk assessment procedure was developed to estimate the fraction of drivers that incurred head and thoracic AIS3+ injuries in full-engagement frontal crashes. The estimates were based on numerical simulations of various real-world events, including variations of crash severity, crash speed, level of restraint, and occupant size. The procedure consisted of four steps: (1) conduct the simulations of the numerous events, (2) use biomechanical equations to transform the occupant responses into AIS3+ risks for each event, (3) weight the maximum risk for each event by its real-world event frequency, and (4) sum the weighted risks. To validate the risk assessment procedure, numerous steps were taken. First, a passenger car was identified to represent average field performance.

This paper describes improvements made to the injury risk curves for peak neck tension, peak neck extension moment and a linear combination of tension and extension moment that produce peak stress in the anterior-longitudinal ligament at the head-to-neck junction. Data from previously published experiments that correlated neck injuries to 10-week-old, anesthetized pigs and neck response measurements of a 3-year-old child dummy that were subjected to similar airbag deployments are updated and used to generate Normal probability curves for the risk of AIS ≥ 3 neck injury for the 3-year-old child. These curves are extended to other sizes and ages by normalizing for neck size. Factors for percent of muscle tone and ligamentous failure stress as a function of age are incorporated in the risk analysis. The most sensitive predictor of AIS ≥ 3 neck injury for this data set is peak neck tension.

Risk curves are developed for several crash data sets, expressing the probabilities of injury as a function of HIC, Extension Moment, Neck Tension and Maximum Deflection, respectively. The statistical method uses concept of thresholds that are interval censored and right censored. A combined evaluation method is used to select a “best” curve among the curves derived from various methods.