DUI: Defining & Understanding “Influence”

Everyone should want a DUI regime that balances public safety with the liberty interests of non-negligent drivers. However, the current systems of assessing driver impairment fall short of that optimal balance when assessing cannabis use. Questions of “THC-impairment” can’t be answered just by a snapshot of THC-levels in the body; knowing what counts as “impairment” requires knowing how drivers’ actual motor-skill, attention and awareness, and information processing are impacted by THC — in FACT, not in rough analogy to alcohol.

We are currently so accustomed to the reigning alcohol-impairment prevention regime that we may unconsciously import biases and assumptions into our assessments.  For example, a New York Times Article on driving under the influence of marijuana opened with the following:

If you are pulled over on suspicion of drunken driving, the police officer is likely to ask you to complete three tasks: Follow a pen with your eyes while the officer moves it back and forth; get out of the car and walk nine steps, heel to toe, turn on one foot and go back; and stand on one leg for 30 seconds.

Score well on all three of these Olympic events, and there’s a very good chance that you are not drunk. This so-called standard field sobriety test has been shown to catch 88 percent of drivers under the influence of alcohol.

But it is nowhere near as good at spotting a stoned driver.

The contrast between being drunk and being stoned resonates with many people, as does the notion that law enforcement officers should be able to identify and punish — and thereby deter — drivers whose level of cannabis-impairment is a threat to public safety.

But this article wrongly assumes that “stoned driver” who passes the field sobriety test nonetheless still deserves to be caught out. The article presumes that a “stoned driver” definitively was impaired and a risk to public safety even though the driver demonstrated sufficient attention, fine and gross motor skills, and calmness under the pressure of a scrutinizing public-safety officer to pass the field sobriety test.

Current research cited in the NYT article highlights the unsettled question of cannabis’ impact on driving risk:

[S]everal researchers, working independently of one another, have come up with the same estimate: a twofold increase in the risk of an accident if there is any measurable amount of THC in the bloodstream.

The estimate is based on review papers that considered the results of many individual studies. The results were often contradictory — some of the papers showed no increase in risk, or even a decrease — but the twofold estimate is widely accepted.

What has been definitively established, however, is that the increased risk posed by alcohol-impairment is an order of magnitude greater than cannabis’:

 A recent study of federal crash data found that 20-year-old drivers with a blood-alcohol content of 0.08 percent — the legal limit for driving — had an almost 20-fold increase in the risk of a fatal accident compared with sober drivers. For older adults, up to age 34, the increase was ninefold.

The study’s lead author, Eduardo Romano, a senior research scientist at the Pacific Institute for Research and Evaluation, said that once he adjusted for demographics and the presence of alcohol, marijuana did not statistically increase the risk of a crash.

Our biases — that alcohol and cannabis are equivalent intoxicants, that being stoned must make driving unsafe — run deep. Mr. Romano, despite having authored the study showing that cannabis didn’t increase the risk of crashes versus the sober-baseline, can’t help but succumb to his cultural common-sense, however non-scientific: “Despite our results, I still think that marijuana contributes to crash risk,” he said, “only that its contribution is not as important as it was expected.”

There surely may be legitimate and persuasive reasons why a “stoned driver” shouldn’t be trusted to operate a motor vehicle, perhaps even if such a driver were able to demonstrate otherwise sufficient “field sobriety” before an experienced public-safety officer. Yet the NYT article author, like Mr. Romano, appears to presume that such a driver, merely by virtue of being “stoned”, represents a public safety risk–regardless of the FST results.

Most cannabis-concerned folks are aware that frequent use is likely to build up THC concentrations in the body to such a degree that your blood-THC content might still be five nano-grams per milliliter a day after you last lit up. And cannabis-users and scientists alike understand that such blood-content has little bearing at all on the only question that should matter: is there good reason to believe that the driver was IMPAIRED at the time of driving?

The public is entitled to protection from those who drive while impaired and it may be necessary to establish a certain level of THC-in-the-body as constituting impairment. But, at a minimum, any such threshold should be based on meaningful and scientific evidence of heightened risk.

However, until we can replace the current regime, cannabis-users must be hyper-conscientious in complying with the current prohibitions. Regardless of the state of legal obligations, every person, cannabis-user or not, should take care when behind the wheel.

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