Legalizing marijuana causes more crashes...or does it?

June 27, 2017

Legal weed is a big deal these days, with advocates claiming that marijuana has the ability to help those with chronic medical conditions and also raise millions in tax dollars. But is all that high praise really warranted?

Two reports issued this week suggest that the answer is a definite "maybe".


First, some bad news for the residents of Stonerville: the Highway Loss Data Institute reports that legalizing marijuana for recreational purposes causes an uptick in car crashes.

To reach that conclusion, the HLDI looked at insurance claims in three states where voters have approved recreational pot usage: Colorado, Oregon, and Washington. To generate the most accurate results, the organization also looked at claim rates before and after marijuana was legalized. It also examined insurance claims in neighboring states where weed was not legal at all (Idaho) or was legal only for medical use (Montana, Nevada, Utah, and Wyoming).

The effects were most noticeable in Colorado, which began allowing retail sales of marijuana in January 2014. The HLDI says that afterward, collision claims in Colorado soared 14 percent compared to neighboring states. The effects were more muted in Washington (where claims rose six percent) and Oregon (up four percent).

When data from the three states was combined and proper controls were added, it showed an increase of three percent in collision claims following the legalization of recreational pot.

The HLDI is in the process of conducting a longer study to assess the impact that legalizing marijuana has on crash severity and fatalities. That report should be published by 2020.

Riding high

And now the good news: a completely different report from the National Highway Traffic Safety Administration appears to contradict the HLDI study. It shows that although the use of drugs like marijuana is increasing, weed itself doesn't play a statistically significant role in causing collisions. Here's the important bit:

"[T]he 2015 Drug and Alcohol Crash Risk Study, initially seemed to find a statistically significant increase in unadjusted crash risk for drivers who tested positive for use of illegal drugs (1.21 times), and THC (1.25 times). However, when the crash risk analysis was adjusted for other well-known risk factors, such as age, gender, race, and ethnicity, there was no longer a statistically significant difference in crash risk associated with the presence of these drugs. This finding indicates that these other variables (age, gender, race, and ethnicity) accounted for the detected increase in risk. This may be due, at least in part, to the fact that young males are more likely to test positive for illegal drugs and marijuana, and they are also more likely to be involved in crashes (Compton & Berning, 2015). Alcohol use was highly correlated with increased crash risk, even after adjusting for other known risk factors." (emphasis ours)

And so, NHTSA is assessing the risks that legalized marijuana--both for recreational and medical purposes--poses to automotive safety. Among the topics that NHTSA will cover are how to determine when someone's driving is impaired by pot; how to test drivers in the field; and how to sentence those found guilty of driving while high. 

That's important for several reasons--most notably because 29 states and the District of Columbia now allow residents to use marijuana for medical purposes; four of those states allow recreational use; and 13 states are either voting on legalized use or are gathering signatures for ballot measures. As legal weed becomes common nationwide, it's important for states and municipalities to have guidelines on best practices.

For example, while we have well-established means of determining blood alcohol content for those suspected of drunk driving, there's no set standard to measure THC levels. (Some states have set five nanograms of THC as the acceptable amount, but courts have thrown out such laws, saying that the limit is arbitrary and that science doesn't support the assertion that impairment occurs at that level.) The NHTSA-led study hopes to address such issues and more.

You can download a PDF of the NHTSA report by clicking here

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