Marijuana Legalization Was Not Linked to Higher Traffic Fatality Rates in a 2016 State Comparison
A 2023 analysis by Quartz Advisors found no increase in traffic fatality rates during the first three years after four states adopted adult-use marijuana legalization in 2016. The analysis compared California, Maine, Massachusetts, and Nevada with national trends and with five states that had not legalized recreational cannabis: Idaho, Indiana, Kansas, Nebraska, and Wyoming.
From 2016 through 2019, traffic fatality rates fell in three of the four legalization states and remained roughly unchanged in Maine. Massachusetts recorded the largest decline, at 28.6 percent. Across the four states, vehicle death rates fell 11.6 percent—slightly more than the 10.6 percent national decline during the same period.
Those figures are descriptive comparisons, not proof that legalization made roads safer. The Quartz analysis did not establish a causal relationship, and the states differed in population, traffic patterns, enforcement, economic conditions, and the timing of commercial cannabis sales. It also relied on a small group of states rather than a peer-reviewed, nationwide research design.
When the analysis was extended through 2021, the picture became less clear. Traffic fatality rates increased in the four legalization states between 2016 and 2021, but the increase—about 6 percent—was slightly below the national rise of 6.2 percent. The selected comparison states, meanwhile, recorded a small decline. Quartz treated 2020 and 2021 separately because traffic deaths rose sharply across the United States during the COVID-19 pandemic, making it difficult to isolate any effect from cannabis policy.
Other research has produced mixed results. A 2022 report from the Casualty Actuarial Society, which examined U.S. and Canadian data, found no statistically significant persistent change in fatalities or insurance-claim frequency after marijuana legalization or decriminalization. Academic studies, however, have reached different conclusions in different settings. For example, a JAMA Internal Medicine study found an increase in traffic fatalities in Colorado but not Washington after recreational cannabis laws took effect.
The absence of a clear population-level increase in fatality rates does not mean cannabis is safe for drivers. A systematic review and meta-analysis published in Addiction found that cannabis alone impaired measures such as lateral control, while combining cannabis with alcohol produced greater driving-performance impairments than either substance alone.
The Centers for Disease Control and Prevention says cannabis can slow reaction time and decision-making, impair coordination, and distort perception. Testing presents an additional challenge: detecting THC in a person’s system does not reliably show when cannabis was consumed or whether the person is impaired at that moment. Unlike alcohol, blood THC concentration does not provide a simple, universally accepted measure of driving impairment.
The evidence therefore supports a cautious conclusion. The Quartz comparison did not find higher traffic fatality rates in the four states that legalized adult-use cannabis in 2016 during 2016–2019, but it cannot show that legalization reduced deaths or had no effect under different conditions. Regardless of a state’s cannabis laws, driving while impaired—and especially combining cannabis with alcohol—remains a significant road-safety concern.
