State-level COVID-19 lockdown stringency associated with increases in motor-vehicle mortality rates

Motor-vehicle collision fatalities increased dramatically during the COVID-19 pandemic in the United States, but significant variation existed between states. The objective of this study was to examine the relationship between state-level COVID-19 public health policy stringency and changes in motor-vehicle fatality rates.

This ecological cross-sectional time-series study used public mortality data from the National Highway Traffic Safety Administration's Fatality and Analysis Reporting System (NHTSA FARS). Our primary exposure was the stringency of COVID-19 lockdown policies, derived from the Oxford University COVID-19 Government Response Tracker (OxCGRT) Stringency Index. The primary outcome was changes in motor-vehicle collision mortality rates, calculated as the rate ratio of 2020 and 2021 to 2018 and 2019. Associations between motor-vehicle collision fatality rate ratios and OxCGRT Stringency Index were assessed using univariate linear regression.

After linear regression, changes in intoxicated driver (β = 0.025, r = 0.33, p = 0.02) and unrestrained/not helmeted (β = 0.013, r = 0.30, p = 0.03) motor-vehicle mortality rates demonstrated a significant positive association with COVID-19 stringency for the age group of 21-34. The regression results showed that 11 out of the remaining 14 groups had a positive association between motor-vehicle mortality and stringency, but none reached statistical significance.

This study shows limited evidence linking state-level COVID-19 policy stringency with motor-vehicle collision fatalities. Adults aged 21-34 exhibited increased intoxicated and unrestrained/not helmeted driving deaths during stricter lockdowns. However, other subgroups and behaviors did not reveal significant relationships.

These findings highlight that while broad associations between lockdown policy stringency and MVC mortality were limited, specific subpopulations, particularly younger adults, may be more susceptible to behavioral changes during periods of heightened social restriction, warranting further investigation and targeted prevention strategies.