A decomposition of the effects of the COVID-19 pandemic on changes in the motor vehicle collision related mortality in Alabama

Background/Objective: Motor vehicle collisions are the leading cause of unintentional injury death in Alabama and at various points during the COVID-19 pandemic there were documented increases in the following risk driving behaviors: speeding, driving under the influence, and seat belt citations. Thus, the objective was to characterize the overall motor vehicle collision (MVC)-related mortality rate in Alabama and the contribution of each component over the first two years of the pandemic compared to before the pandemic by three different road classes: urban arterials, rural arterials, and all other road classes.Methods: MVC data were derived from the Alabama eCrash database, an electronic crash reporting system used by police officers across the state. Data on vehicle miles traveled each year were collected from the U.S. Department of Transportation's Federal Highway Administration estimates of traffic volume trends. MVC-related mortality in Alabama was the primary outcome and year of MVC was the exposure. The novel decomposition method broke down population mortality rate into four parts: deaths per MVC injury, injury per MVC, MVC per vehicle miles traveled (VMT), and VMT per population. Poisson models with scaled deviance were used to es-timate rate ratios of each component. Relative contribution (RC) of each component was calculated by taking the absolute value of the component's beta coefficient and dividing by the sum of the absolute values of all com-ponents' beta coefficients. Models were stratified by road class.Results: Across all road classes combined, there were no significant changes to the overall MVC-related mortality rate (per population) and its components when comparing 2020-2022 to 2017-2019; this was due to the increased case fatality rate (CFR) being offset by decreases in the VMT rate and MVC injury rate. In 2020, among rural arterials a non-significant increased mortality rate was offset by a decreased VMT rate (RR 0.91, 95% CI 0.84-0.98, RC 19.2%) and MVC injury rate (RR: 0.89, 95% CI: 0.82-0.97, RC: 22.2%) when compared to 2017-2019. For non-arterials, a non-significant decreased MVC mortality rate was observed in 2020 when compared to 2017-2019 (RR 0.86, 95% CI 0.71-1.03). When considering 2021-2022 versus 2020, the only significant component for any road class was a decreased MVC injury rate for non-arterials (RR: 0.90,95% CI: 0.89-0.93) but this was offset by an increased MVC rate and CFR, resulting in no significant change to the mortality rate (per population).Conclusions: In a state with one of the highest MVC-related mortality rates in the country, despite decreases in VMTs per population and injuries per MVC, the MVC mortality rate per population did not change during the pandemic due in part to the contributions of an increase in the case fatality rate. Future research should determine whether the increase in CFR was associated with risky driving behaviors during the pandemic.