How many people are injured and killed as a result of aging? Frailty, fragility, and the elderly risk-exposure tradeoff assessed via a risk saturation model.

Crash protection for an aging population is one of the primary drivers of contemporary passive safety research, yet estimates of the potential benefit of age-optimized systems have not been reported. This study estimates the number killed and injured in traffic crashes due to the age-related reduction in tolerance to loading. A risk-saturation model is developed and calibrated using 2000-2007 data for the age distribution of crash-involved adult occupants and drivers and the number of those injured and killed in 2006. Nonlinear functions describing the relationships between age and risk, adjusted for several confounders are developed using 10 years of NASS-CDS data and considered along with published risk functions for both mortality and injury. The numbers killed and injured as a result of age-related fragility and frailty are determined by setting the risk at all ages equal to the risk at age 20 (i.e., risk is assumed to "saturate" at age 20). The analysis shows that risk saturation at age 20 corresponds to 7,805-14,939 fewer driver deaths and 10,989-21,132 fewer deaths to all occupants. Furthermore, 1.13-1.32 million fewer occupants would be injured (0.80-0.93 million fewer drivers) per year. In other words, that number of deaths and injuries can be attributed to age-related reductions in loading tolerance. As the age of risk saturation increases, the benefit decreases, but remains substantial even in the age regime typically considered "elderly". For example, risk saturation at age 60 corresponds to 1,011-3,577 fewer deaths and 73,537-179,396 fewer injured occupants per year. The benefit of risk saturation is nearly log-linear up to approximately age 70, but drops off quickly thereafter due to the low exposures in the oldest age range. The key contribution of this study is the quantification of deaths and injuries that can be attributed to aging and the development of functions describing the relationship between age of risk saturation and the number of deaths and injuries averted.