Driving Under The Influence Of Marijuana In California


Driving under the influence of marijuana is an evolving subject of concern to safety experts and law enforcement. Last week I wrote about the difficulties California and other states are having establishing at what levels marijuana use presents a driving risk and how those risks are assessed. There is yet to be a consensus. This has happened before. In the 1930’s and 40’s as automobile ownership reached the masses, there was no general agreement among the states regarding drunken driving and until the 1950’s no reliable way to measure a driver’s level of inebriation. Before the advent of the breathalyzer, whether someone was too drunk to be on the road was left to the subjective decision of law enforcement and all too often, that mean the officer would just follow the driver home to make sure he or she made it home safely.

With the legalization of marijuana, we face similar dilemmas, and just like the early days when drunken driving laws were evolving, there is yet to be a reliable method to test a driver for marijuana testing and there is no agreed-upon limit where THC levels are considered too high to drive. In the mid-twentieth century, there were honest debates about whether a moderately intoxicated driver was dangerous and most states, even up to the late 1960’s, did not prosecute a driver if his or her BAC was under 0.15%. Statistical analysis and scientific studies later established that a BAC over 0.08% makes a driver dangerous and the trend is going lower, towards a 0.05% BAC threshold.

So why do I bring all of this up? It’s “déjà vu”. As I mentioned in last week’s blog post, the research is unsettled on the marijuana effects on drivers with some studies even suggesting that drivers under the influence of marijuana are actually more cautious than sober drivers.

But the National Academies Sciences recently published a compressive “Consensus Study Report” that concludes that there is substantial evidence that links cannabis use with increased motor vehicle accidents. This study looked at systematic reviews of research studies on the effect of marijuana on driving from 2007 to the present across many countries. According to this review, the presence of THC in a driver’s system presented 20 to 30 percent higher odds of being involved in a motor vehicle crash. As noted, however, there are limitations to these findings due to controversy over the association between THC levels in a person’s system and intoxication or driving impairment.

The report also considered laboratory and simulator studies, which can control for when and how much THC is ingested prior to the study. There it was found that the psychomotor skills necessary for safe driving were increasingly compromised with higher doses of THC. But as the report noted, these results may not transfer to real-world applications as there are variables that can’t be accounted for in the lab.

When drunken driving at what we now know are dangerous levels was still considered relatively safe, many people, even the cops, didn’t worry too much about “one for the road.” Now we know how dangerous drunken driving is. Before the states started tightening up on drunken driving, drunk drivers were involved in close to 50 percent of all traffic fatalities in this country. Now that statistic is closer to 30 percent. Will driving under the influence of marijuana go through a similar evolution. I suspect it will. While driving under the influence of marijuana is illegal, there is no objective measure of “influence.” The safest bet is to treat being under the influence of marijuana just like you would treat being under the influence of alcohol: Designate a sober driver.

William Weinberg has been defending DUIs and DUID cases in Orange County for almost 25 years. He is available for a free consultation. Contact Mr. Weinberg at his Irvine office at 949-474-8008 or by email at bill@williamweinberg.com.

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