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The effects of recreational marijuana legalization on driving under the influence of marijuana in a neighboring state: A cross-border quasi-experiment
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DOI：10.1016/j.jsr.2026.03.005.png)
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Abstract
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Objectives: This study examines whether recreational marijuana (RM) legalization in neighboring states is associated with driving under the influence of marijuana in a non-legalizing state, as measured by motor-vehicle crashes involving a marijuana-positive driver (MP). Methods: Although Pennsylvania has not legalized RM, it borders five states that legalized RM at different time points in 2021 and 2023. This spatial and temporal variation enables a quasi-experimental stepped wedge design that assesses whether Pennsylvania counties that border a state with RM legalization experienced changes in MP motor-vehicle crash counts. Pennsylvania Department of Transportation data provide crash counts at the county-month level (January 2019-December 2024). Of primary interest are MP crashes where the Pennsylvania State Police (PSP) was the reporting law enforcement agency (MP-PSP). Once RM legalization occurs in a contiguous state, a Pennsylvania county (N=27) bordering that state becomes Post-Exposure. Four Pennsylvania counties eventually bordered two states with RM legalization, becoming Post-Second-Exposure. Poisson regression was used to estimate changes in crashes in the Post-Exposure and Post-Second-Exposure periods relative to the Pre-Exposure period. Results: On average, a Pennsylvania county experienced a significant 58.41% increase in MP-PSP crashes Post-Exposure and a nonsignificant 55.48% increase Post-Second-Exposure. Where a border county has an interstate highway (N=20), on average, there was a significant 68.95% increase Post-Exposure and a nonsignificant 56.80% increase PostSecond-Exposure. Practical Applications: RM legalization in bordering states may impact traffic safety in a state that has not yet legalized RM. Future research should identify mechanisms for this association as well as actionable strategies to prevent marijuana-impaired driving.
Keywords:
Marijuana
Motor-vehicle crashes
Traffic safety
Borders
Driving under the influence
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