Work

The effects of recreational marijuana legalization on driving under the influence of marijuana in a neighboring state: A cross-border quasi-experiment

Year: 2026

Type: article

Abstract: 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 Post-Second-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.

Source: Journal of Safety Research

DOI: 10.1016/j.jsr.2026.03.005

Author: Ruth A. Moyer

Institution: University of Pennsylvania

Language: English

Topic: Traffic and Road Safety

Subfield: Safety, Risk, Reliability and Quality

Field: Engineering

Domain: Physical Sciences

SDGs: Peace, justice, and strong institutions, Good health and well-being

Open Access status: hybrid

Estimated APC paid: $3,220