I’ve been waiting to hear about Iowa driving simulator studies for a while now.
Time reports: How Much Does Marijuana Impact Your Driving?
The researchers looked at 250 parameters of driving ability, but this paper focused on three in particular: weaving within the lane, the number of times the car left the lane, and the speed of the weaving. While alcohol had an effect on the number of times the car left the lane and the speed of the weaving, marijuana did not. Marijuana did show an increase in weaving. Drivers with blood concentrations of 13.1 ug/L THC, the psychoactive ingredient in cannabis, showed increase weaving that was similar to those with a .08 breath alcohol concentration, the legal limit in most states.
The fact that this paper focused on three of the 250 parameters of driving ability means that we’ll probably be getting a lot more of these in the future.
The concern to me is not learning actual science, but more often how the science is presented or skewed (junk science). I don’t doubt that the science at the National Advanced Driving Simulator in Iowa is rigorous. But I do have concerns about how it will be used, particularly based on the agenda of its funder (NIDA) and its lead researcher (Marilyn Huestis).
So, basically, this particular paper looked at SDLP (standard deviations of lateral position) and concluded that cannabis didn’t have nearly the effect of alcohol, even at fairly high levels, and yet, according to the researcher:
Huestis believes that the 5 ug/L limit is not strict enough, particularly when you take into account those with low tolerance.
Of course, also not mentioned in the article is a small point that was brought up in the study:
“SDLP is not directly validated to predict crash risk”
Ah, yes. SDLP results don’t necessarily equate to unsafe driving. It is simply an interesting variable worth looking at. That didn’t, however, stop the researcher from giving the opinion that marijuana driving laws are too lax. We’re likely to get a lot of that.
I remember when I first heard about the long-term simulator study in Iowa: University of Iowa testing effects of pot on drivers (the date of the article online wrong, it was actually September 9, 2012). I wrote to Marilyn Huestis back then, but never got a response.
What I wanted to know was whether the simulator would assess actual overall safety of driving or whether it would simply focus on elements of driving that were different. For example, stoned drivers are known to slow down because they tend to be aware of their condition (much more so than those on alcohol), but a simulator test could well interpret that caution as failure.
Based on the first results to come from the simulator, I think we have our answer.
I had additional concerns about Huestis based on this article back in 2013:
While the majority of scientists say the effects of marijuana dissipate relatively quickly, Huestis reports that both THC and impaired performance linger in the brains of daily users for weeks after their last puff. The chronic users Huestis observed were still excreting THC from their tissues even after a month of abstinence, and did not respond as well as the control group in psychomotor and divided attention tasks.
“Individuals may say they haven’t used cannabis in a day, a week, whatever—but guess what? Your brain is still recovering and changing from that abstinence,” said Huestis in a phone interview. “Some people might ask what that has to do with real driving ability. Well, now we have data to show that it affects psychomotor impairment.”
Huestis sees support for her work in several studies done throughout Europe, and Australia, but to those familiar with the bulk of the literature, Huestis’s claims have left many shaking their heads—especially considering the influence it would have on policy.
According to Heustis’s conclusions, all regular cannabis consumers—including patients who have demonstrated a medical necessity—would automatically become a traffic risk in the eyes of the law even after weeks of abstinence.
Yeah, that’s not someone I trust to present cannabis-related science fairly.