Traffic fatalities fell in states that legalized marijuana, while those that maintained criminalization saw a “slight increase,” according to a new study.

States that legalized marijuana in 2016 saw significant declines in traffic fatalities in the years immediately following the policy change, according to a new study from Quartz Advisor. But the findings were less clear over a longer period of time, spanning years that the report describes as “anomalies” across the country.

Ultimately, the paper concludes that motor vehicle safety “should not be a significant concern in marijuana legalization initiatives,” particularly when compared to alcohol.

“To date, studies have not shown that the legalization of cannabis has resulted in a significant increase in traffic fatalities in the places where it has been legalized,” it said. “But the same cannot be said for alcohol, an intoxicant that remains legal, widespread and deeply embedded in our culture.”

In states where marijuana was legalized, “traffic fatalities declined or remained the same over the following three years, while states where marijuana remained illegal saw a slight increase.”

The findings, which were not peer-reviewed, examined traffic fatality data from four states that legalized adult-use cannabis in 2016: California, Maine, Massachusetts and Nevada. Quartz Advisor then compared these states’ traffic fatality rates to the national average, as well as to rates in five states where marijuana remained illegal during that period: Idaho, Indiana, Kansas, Nebraska and Wyoming.

In the three years after the change, the report says, none of the four legalized states saw an increase in traffic fatalities. Most actually experienced declines.

“Three of the four states saw significant declines in traffic fatalities during this period,” the paper says, “while the rate in Maine did not change.” The largest decline was in Massachusetts, where rates fell in the three years after legalization 28.6 percent fell.”

Combined, the four states that legalized marijuana saw an 11.6 percent decrease in traffic fatality rates from 2016 to 2019. That’s a steeper decline than the national average, which fell 10.6 percent over the same period.

That’s a far better result than in the five states the report examined where marijuana remained illegal and which collectively saw a 1.7 percent increase in traffic fatality rates from 2016 to 2019.

But what might seem like a clear picture became murkier when researchers expanded the analysis to include data from 2020 and 2021, the most recent years for which figures from the National Safety Council (NSC) were available. During this period, traffic fatalities actually increased in states that legalized marijuana, although less than in the U.S. as a whole. In states where cannabis was illegal, the number of traffic deaths fell.

“Among states that legalized marijuana in 2016, the traffic fatality rate increased 6.0 percent between 2016 and 2021,” the report said. “While this is an increase, it is slightly lower than the national average, which saw a 6.2 per cent increase in the road fatality rate over the same period. In the five states that did not legalize cannabis during this period, vehicle fatality rates fell by an average of 0.7 percent.”

Why consider ignoring two whole years of data? The report explains:

“The years 2020 and 2021 were anomalies in many ways, and this also applies to the evolution of car accidents. After decades of declining accident rates in the U.S., traffic fatalities rose in 2020 and remained high through 2021. In the U.S. as a whole, traffic fatality rates increased by 18.9 percent from 2019 to 2021. States that legalized marijuana in 2016 saw a similar increase of 18.9 percent to 19.9 percent. In states that have not yet done so – and which are significantly more rural than those that have – the traffic fatality rate fell by 2.3 percent over this period.”

“For this reason, we thought it was important to see what the rates look like when 2020 and 2021 are removed from the data set,” it continued. “And it turns out they look completely different.”

Quartz Advisor called the observations “interesting and nuanced – but ultimately limited.” So the publication spoke with Judi Watters, public information and consumer protection officer for the Maine Bureau of Insurance, who cited a December 2022 report from the Casualty Actuarial Society that examined U.S. and Canadian data from 2016 to 2019.

“The tests of decriminalization effect on deaths failed to detect a statistically significant change,” the 2022 report said of its U.S. results. Likewise, the analysis showed “no statistically significant changes in average cost per claim and claim frequency following marijuana legalization in Canada.”

Quartz Advisor’s new report states: “Although there is no evidence that legalizing or decriminalizing marijuana makes the roads more dangerous, that does not mean it is safe to drive while under the influence of cannabis.” It refers to one Meta-analysis published in 2010 in the American Journal of Addictions found that marijuana “causes impairments in all performance domains that can reasonably be associated with the safe operation of a vehicle.”

Strangely, however, this does not always seem to make driving behavior correspondingly more dangerous.

The 2022 Actuarial Accident Insurance Study found that while marijuana use has an impact on driving, “the behavior is not always riskier; For example, slower speeds and longer following distances of impaired drivers have been reported.”

The American Journal of Addictions report contains a similar caveat:

“Given the alarming results of cognitive studies, it is surprising that most marijuana-intoxicated drivers show only minor impairments in actual road tests,” it says. “Experienced smokers who drive a fixed route show almost no functional impairment under the influence of marijuana.”

Above and beyond the widespread concerns about cannabis-related driving impairment is the fact that there is no reliable test that specifically screens for cannabis-related impairment. Standard drug tests make it difficult or impossible to know whether someone is under the influence of marijuana or has used it days or even weeks ago.

This summer, a congressional report for the Transportation, Housing, Urban Development, and Related Agencies (THUD) bill said that the House Appropriations Committee “continues to propose the development of an objective standard for measuring marijuana impairment and an associated field sobriety test.” Location supported.” Ensuring road safety.”

In February, the head of the American Trucking Association (ATA) discussed the issue with a congressional committee, arguing that lawmakers needed to “step in” to address the conflict between state and federal cannabis policies as the industry faced shortages.

Tens of thousands of truck drivers are testing positive for marijuana as part of federally mandated testing, Department of Transportation (DOT) data shows.

Sen. John Hickenlooper (D-CO) sent a letter to the DOT last year asking for an update on the status of a federal report on research obstacles hampering the development of a standardized test for marijuana roadside impairment. Under a sweeping infrastructure bill signed by President Joe Biden, the department must complete the report by November.

Experts and advocates have emphasized that there is no clear evidence linking THC levels in the blood and impairment.

For example, a study published in 2019 concluded that those who drive at the legal THC limit – which is typically between two and five nanograms of THC per milliliter of blood – are statistically no more likely to be involved in an accident than people who do this have not consumed marijuana.

Separately, the Congressional Research Service noted in 2019 that “while marijuana use can impair a person’s reaction time and motor performance…studies on the effects of marijuana use on a driver’s risk of being involved in a crash have yielded conflicting results.” led, with some studies coming to the conclusion: “little or no increased risk of accidents due to marijuana use.”

Another study last year found that smoking CBD-rich marijuana had “no significant effects” on driving ability, even though all study participants exceeded the per se limit for THC in their blood.

This article originally appeared on Marijuana Moment.