Marijuana Impairment DUI Arrests Face Challenges Due To Inaccurate And Unproven Impairment Studies

By Darren Smith, Weekend Contributor

Marijuana LeafThe standard for which Marijuana Impairment presumptive levels in DUI prosecutions are likely to be under scrutiny due to what some are regarding as unproven scientific evidence. Presumptive impairment levels for THC concentration in blood samples might not satisfy legal requirements from an actual driving impairment perspective. They could in-fact be regarded arbitrary and not scientifically supported.

States do have the legal authority to establish presumptive impairment levels, that is a measurable quantity of a substance sufficient to establish an element of DUI. In fact while the present presumptive alcohol level in the United States for ordinary drivers is .08, states have established .04 for commercial vehicle driving and some states have .02 for those under twenty one years of age who violate analog status offenses that do not define impairment as an element.

Now, the American Automobile Association’s Foundation for Traffic Safety cited a study that differences between individuals can be wide and greatly varied regarding impairment at a set blood THC level. While some drivers show obvious signs of impairment at low levels of THC blood concentration, other persons can have greatly elevated readings and show no outward appearance of signs of DUI.


In the case of driving impairment by reason of ethyl alcohol concentration, decades of various studies have shown a direct relation between blood alcohol levels and DUI impairment. Studies on THC impairment are alas comparatively novel. There is however a level of tolerance of course with nearly all intoxicating substances, some marked, which of course presumptive alcohol concentration level statutes fulfill the required element for DUI prosecution.

On of the first generally used presumptive DUI alcohol concentration level in many states for a reading of breath was .10 grams of alcohol for each 210 liters of breath. Further studies recommended the presumptive level be reduced to .08. The federal government then pressured the states to lower the presumptive levels.

The Recreational Marijuana states: Washington; Colorado; and Montana, place the presumptive THC level at 5 nanograms per milliliter of blood.

The AAA findings suggested, in part, that performing direct comparisons with alcohol impairment is problematic.

Since the time required to administer a THC blood test is often two hours or more after the suspected driving, as compared to breath tests, levels of the intoxicant can drop rapidly. Conversely the study cites that infrequent users of marijuana tend to metabolize THC faster than heavy users, who might in fact carry loads of THC well in excess of 5 nanograms but show no outward impairment. AAA’s position was that such testing and enforcement leads to an unequal treatment of persons when a presumptive level is used.

Another AAA study, released in 2015, found that fatal collisions involving drivers who recently used marijuana had doubled in Washington since the state legalized individual possession in 2012: from eight percent to seventeen percent. Most of the drivers, according to the study, had alcohol or other drugs in the blood at the time of the collision.

In the view of your author there are some weak points in this study. AAA stated that the drivers were not necessarily impaired by marijuana nor were at fault in the collisions. Additionally, in Washington a mandatory blood draw is triggered when a driver is suspected of reckless driving or DUI that results in a fatality. A search warrant also might be obtained or a driver can voluntarily submit to a blood test in lieu of a breath test. There are opportunities where no impairment would be indicated in a test where a positive level of THC is found in a driver’s blood. This is especially evident in cases of Reckless Driving not involving DUI. It usually is the case where alcohol is the primary intoxicant, yet even a minor level of THC will flag the test for this study.

Moreover, arrests for DUI where marijuana impairment prior to legalization was in some jurisdictions uncommon or rare. But, these certainly rose due to the wider availability. It is however difficult to accurately measure a history of non-collision involved DUIs where both marijuana and alcohol are might have been contributory to impairment. Standard practice in DUI enforcement is when alcohol is suspected as being over a presumptive level, despite the presence of other drugs, the de facto rule is to process the suspect only for alcohol impairment due to time and resource constraints. Since only the alcohol tests are required for a DUI element that is all that needs to be satisfied. Thus, historical usage and levels of THC concentration will be difficult to quantify.

By Darren Smith

Source: The Olympian

The views expressed in this posting are the author’s alone and not those of the blog, the host, or other weekend bloggers. As an open forum, weekend bloggers post independently without pre-approval or review. Content and any displays or art are solely their decision and responsibility.

19 thoughts on “Marijuana Impairment DUI Arrests Face Challenges Due To Inaccurate And Unproven Impairment Studies”

  1. So wAit when i caught the cops all wide eyed and bushy tailed sneaking around my porch without a warrant they could have been high? And there is no drug test for that?

  2. Steve Groen

    You bring up two pertinent points.

    Washington State’s supreme court tossed public intoxication laws back in the 1980’s, citing essentially that the state was punishing for a biological function and that the state could articulate no public interest in regulating a person who was merely intoxicated. Furthermore, nearly all other intrusions into a person’s body, except for mostly DUI type offenses, require a search warrant. This includes swabs of a person’s mouth for DNA profiling (except in cases of commitment to the state for a felony) and medical procedures to retrieve bodily fluids.

    I don’t know exactly how urine samples are dealt with regard to warrantless searches, but I suspect they must be requested unless the person is under the supervision of the DOC. We had an appellate case (I don’t remember off-hand the citation) where a person (the suspect) was ordered to retrieve an item from their curtilage that otherwise would have required a search warrant by the police, the person was ruled to be acting as an instrument of the state and the search was suppressed. I can see this being argued for urine samples if the person provided the sample under protest.

    For DUI mandatory blood draws they originate out of implied consent as a condition of being issued a driver’s license. As you indicate the courts consider driving on state highways to be a privilege so it has upheld implied consent. I suspect if the courts ever decided driving is a form of right then implied consent will disappear. Oddly, a person may walk on a sidewalk virtually unimpeded by the state but if they ride a bicycle, which is not required to be licensed, they are subject to traffic law.

    For commercial vehicles one of the reasons cited for the .04 presumptive CDL DUI level is that these type of vehicles are very capable of causing great amounts of damage and injury due to their size and the items transported. In fact, state departments of licensing will issue CDL (commercial driver’s license) suspensions based upon the type of material transported. If the driver is carrying hazardous material they can face a lifetime revocation of their CDL. There is a situation where a person might have their CDL suspended but retain their personal driver’s license (PDL) That can happen for presumptive readings between .04 and .079. The CDL might be suspended but their personal license will stay. But if they are driving a commercial vehicle while over the legal intoxicated limit, then a standard DUI can be enforced and they will lose both licenses.

    1. Darren writes, “For commercial vehicles one of the reasons cited for the .04 presumptive CDL DUI level is that these type of vehicles are very capable of causing great amounts of damage and injury due to their size and the items transported. In fact, state departments of licensing will issue CDL (commercial driver’s license) suspensions based upon the type of material transported. If the driver is carrying hazardous material they can face a lifetime revocation of their CDL.”

      Thanks for the interesting follow-up. I get the reasoning behind commercial versus personal BAC limits. I just don’t think it’s rational. First, there should be zero tolerance for alcohol when driving hazardous materials; and, 2) “great amounts of damage and injury” can be caused by anyone, not just carriers of goods, driving down the sidewalk in Santa Monica. That’s why I have a more than a suspicion the drafting of these laws have been influenced by the alcohol and food and beverage industries.

      And, on the related issue, I fully support some time of regulation of THC while driving, but is there really a need for invasive DUI testing for pot? Wouldn’t a standard field sobriety test satisfy the standard? I think pot use while driving is more an issue of taking one’s mind off the task of driving, by daydreaming more than anything else, similar to texting messages while driving, and rather than DUI prosecution it should be viewed as criminal negligence/recklessness.

      For instance, LEO sees dude swerving onto the shoulder or another lane already occupied, and not reacting fast enough. Sounds like a ticket or worse to me.

  3. Karen S.- As far as I known, marijuana is still grouped with heroin, cocaine, etc. as a Schedule 1 restricted drug under federal law.
    Researchers have complained that the Schedule 1 classification greatly complicate their efforts to do research/ trials.

  4. If you use, do not drive for 2 days. I’m a pedestrian.

  5. Plus different combinations of drugs and alcohol can have a synergistic effect.

  6. Nick – good point. It would be really difficult to test for impairment rather than quantitative. DUI standards are far behind marijuana laws.

    Since cannabis was illegal until fairly recently, it was not a material used in very many research labs. So even though it has a long history of use, there is not a long history of data.

  7. One issue I’ve not seen extensively discussed is the consumption side vis-a-vis alcohol. Alcoholic beverages fall into generally recognizable/accepted ranges in terms of consumption. BAC can be reasonably estimated by the consumer based on body weight and number of standardized drinks. Marijuana strength has increased exponentially over the years, so how much can one consume before reaching a blood concentration of “intoxicated?” Same for ingestibles.

    And one gripe I have about the legalization laws currently in effect or proposed is that they’re based on weight (ounces or grams) of product, without regard for potential effects.

  8. Neighbordave, You got a high THC tolerance level?

    Pot, Afghanistan hashish, hash oil, spiked weed that is modified, makes driving dangerous.

    Price of body bags are cheap.

  9. Jerry, Really, plain unadulterated weed, that gives you the same effect as LSD?
    LSD is an entirely different reality so I don’t think you should put that out there.
    Back in the sixties I did both, including some Thai sticks and Hawaiian weed, which was the best we could get then. Nothing even close to LSD, which made the ceiling fluctuate like spaghetti, etc.

  10. You don’t think folks are modifying pot products?

    Watch out for the Thai stick. Weed spiked with opium.

    It tastes somewhere between vinegar, marijuana, and flowers. The scent that comes off the bowl is very small to non-existant, and doesn’t smell like incense burning. It crackles a little bit when lit, but does not bubble.

    Don’t drive after smoking this stuff. Stay at home.

  11. “Toxicologist’s Wash. History may taint Calif. Cases”.- from May 25, 2010 Seattle Times.
    I previously mentioned the WA. State crime lab scandal of c. 2008.
    There were at least 2 resignations of top crime lab officials in the wake of the scandal.
    Both of these officials got similar jobs in other states.
    The article I cited here talks about Ann Marie Gordon’s “new” position as forensic toxicologist for San Francisco.
    Her history in WA. State was either not checked, or not a disqualifier.
    My concerns about crime lab testing, BAC or THC levels, go beyond their arbitrary nature.
    I think forensic fraud is a bigger concern, and the events covered in this article show just how sloppy controls for “scientific” crime lab testing can be.

  12. Darren, an interesting post. It appears DUI laws are way behind medicinal/recreational-pot-use laws. There’s certainly a need to regulate driving under the influence of THC if my long-term, empirical data is valid. I’m not big into blood testing however, Breathalyzers are invasive enough if not overly so, but driving is a privilege, so I suppose blood testing is reasonable.

    Digression: By the same token, taking someone into custody, who’s done nothing more than walk down the street and who isn’t exercising a privilege but an inalienable right to privacy in his or her bodily integrity, should not be subjected to blood draws, involuntary emesis, stomach pumping, and other such nonsense, which seems to me beyond the limitations on government set by our federal Constitution. I’m reminded of Justice WO Douglas’s concurring opinion in Rochin v. California where the Court laid out in Justice Frankfurter’s majority opinion the “shock the conscience” test for unconstitutional overreach (since overruled). Justice Douglas and Justice Black felt that it was a violation of the defendant’s Fifth Amendment right against self-incrimination, and so do I.

    I can only guess that the reason a commercial driver’s lawful blood alcohol content level is lower than Joe Six Pack’s is that he or she is hauling someone else’s precious cargo, whether human or chattel, and the relative increase in time spent driving. It begs the question ‘why is there a difference in lawful BAC between commercial and non-commercial driver, who both have been vetted by the state licensing agency and who both can hit a pedestrian just as easily as the other?’ It seems to me that the disparity in these laws is to protect business establishments selling alcohol. This Saturday, June 4th, such laws make no sense to me. Perhaps tomorrow they may.

  13. Pot impairment is an issue with driving a vehicle or using machinery.

    Some weed is so potent, it can produce out of the body sensations and psychedelic illusions just like LSD.
    Stories of the disappearing telephone pole or magic chain saw don’t have happy endings.

  14. Tolerance is something not acknowledged in BAC tests. Let me say up front, I have seen the ravages of drunk driving more than almost all folks and I am hardcore on the subject. However, a heavy drinker w/ a .08 BAC is significantly less impaired than an occasional drinker. That’s something the law has never dealt w/. I get it. You need uniform standards. Well, it’s even more difficult in coming up w/ tests and standards on cannabis. A Heavy cannabis user will have illegal limits of THC in their system even if they don’t use cannabis for 12 hours, and have no impairment. At least w/ alcohol, it leaves our bodies quickly @ a fairly uniform rate for all.

  15. Grammar Nazi here: you don’t need a hyphen in the phrase “in fact.” In that clause it stands as a normal adverbial prepositional phrase.

  16. If government would focus on Smartphone distracted drivers we would be safer and the world would be better off. Distracted drivers. Pot is the least cause. Smile when you crash.

  17. I think .15 BAC was the legal limit in Washington State, and many others, in the 1970s.
    If I remember correctly, it was then lowered to .10, then .08 over the years.
    Given the major scandal in the Washington State crime lab, about 8-10? years ago, I think a number of DUI convictions were challenged.

Comments are closed.