Why have fatality rates among older drivers declined? The relative contributions of changes in survivability and crash involvement.

OBJECTIVES This study examined the trend in fatality rates per vehicle miles traveled (VMT) among older drivers relative to middle-aged drivers and quantified the contributions of changes in crash involvement and survivability to this trend. METHODS Using U.S. national databases, changes in driver deaths per crash involvement (marker of death risk when involved in a crash) and crash involvements per VMT (marker of crash risk) from 1995-1998 to 2005-2008 among older drivers aged 70 and over relative to changes among middle-aged drivers aged 35-54 were computed. The contributions of these components to the relative changes in older drivers' fatality rates per VMT were calculated using the decomposition methodology. RESULTS Fatality rates per VMT declined more among older drivers than among middle-aged drivers over the study period. Relative to middle-aged drivers, drivers aged 75 and older experienced large declines in crash risk and modest declines in death risk. Relative declines in crash risk accounted for 68-74% of the larger decline in fatalities per VMT among drivers aged 75 and older compared with middle-aged drivers. Drivers aged 70-74 experienced modest relative declines in crash risk and death risk. Declines in death risk among drivers aged 75 and older relative to middle-aged drivers were much larger in side-impact crashes; improvements in crash survivability accounted for nearly half of the relative decline in fatality rates in these crashes. Relative survivability did not change significantly in frontal impacts. Higher death risk was more important than higher crash risk in explaining older drivers' elevated fatality rates per VMT relative to middle-aged drivers during 1995-1998, and the contribution of heightened death risk was even greater during 2005-2008. CONCLUSIONS Many factors may have reduced crash involvements among drivers 75 and older, including changes in travel patterns, health, and roadway design. In side impacts, side airbags and reduced passenger vehicle incompatibility may have improved survivability for older drivers. Because excess fragility now makes an even larger contribution to older drivers' elevated fatality rates, future countermeasures that improve survivability can likely provide large benefits.

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