EDITORIAL: Driving while high limits nothing but a low point in science and fairness

The erroneous science behind Fields’ bill could lead to serious consequences for Colorado drivers who really weren’t intoxicated or impaired while driving a car

State lawmakers keeping after the right problem can’t seem to avoid coming up with the same wrong answers.

This time, it’s Aurora state Rep. Rhonda Fields who’s trying to make sure that the roads are as safe as possible as the state gears up to make marijuana legal, and the party gets started in earnest.

MarijuanaFields is sponsoring a measure that would treat marijuana consumption very similar to that of alcohol when it comes to driving. Her bill, which seems poised to pass in the state House, would set a blood-level limit for THC, the substance in marijuana that makes people feel high. If you’re caught driving with a blood-THC level above 5 nanograms per milliliter of blood, you would face a charge of driving under the influence of drugs.

Here’s the problem, whereas there is a huge body of science supporting the seemingly arbitrary numbers behind drunk-driving limits and laws, no such science exists with marijuana.

There are some studies, but they’re not definitive, and they’re really not even very reliable.

The bigger problem is twofold: the erroneous science behind Fields’ bill could lead to serious consequences for Colorado drivers who really weren’t intoxicated or impaired while driving a car, and worse yet, the 5ng/ml limit could just as easily allow for very impaired drivers to hit the roads.

Alcohol and THC are two very different substances that affect different parts of the brain in very different ways.

What little reliable science there is in trying to determine blood-THC levels and impairment show that occasional users exhibit substantially lower THC levels, sooner, after smoking pot, than do frequent and heavy users. That’s unlike alcohol, which is not stored in the body the same way THC is. Even though the stored, inactive, THC does not make people high, it is detected in blood tests the same way.

All this means that those who smoke more pot, for either recreational or medical purposes, face a very real chance of having a higher-than-allowed blood-THC level, even though they’re not high, and not “impaired.”

Imposing this level without better science and better answers is not just unfair, it’s plain wrong.

We agree that trying to make allowances for people to consume “some” alcohol or marijuana and still drive a car is a sketchy public policy, but it addresses the reality of a society where alcohol is plentiful and accepted, and driving somewhere to get it is commonplace. It’s not unrealistic to expect that marijuana use in Colorado will follow similar suit. In that vein, scientists and the government have offered a wide range of recommendations to the public, helping them gauge how much alcohol to drink and under what circumstances before getting behind the wheel of a car. It’s part of the Colorado driver test. We agree that the best advice is, don’t drink and drive, and don’t get high and drive. But the iffy science behind Field’s bill begs the question, “for how long?”

There are no clear answers here, and so making law with such serious consequences is a serious mistake.

It’s already against the law to drive a car while under the influence of drugs or alcohol. That allows for police to give roadside tests in addition to testing for the presence of THC in the blood. But to choose a THC limit based on political need rather than sound research doesn’t do the job.

Lawmakers must either wait for credible research to allow for blood-level limits, or find a more scientific way to determine intoxication. As inconvenient as it is, science must prevail over politics.

  • Soccermom

    Police and law enforcement need a measurement by which a person who is smoking or eating pot can be held responsible for their impairment. At this time the legislature needs to use the information available to set a limit on THC in a persons system. If future information shows that this limit is too restrictive or lenient, it can be changed at a later date. We have to start somewhere otherwise there would be a nightmare for law enforcement to prove that someone was impaired from pot use. Ideally there should be NO THC in a drivers system!!! If someone is using pot they should not be driving.

    • Berticus

      Why would it be a nightmare for law enforcement to need to prove their allegations of impairment by providing actual evidence and testimonial to support their assertions? Nobody said it’s supposed to be easy. This bill gives the cops an easy out and perpetuates awful law enforcement practices. They can haul you in for a blood test for running a stop sign or even merely speeding, didn’t you know?

      • Do you want to be the guy getting the unfair DUI while the law tests a limit that they know is unjust. Studies show drivers using marijuana get into accidents at the same rate as straight drivers. DUI is about how much is too much. Why do we need a blood test anyway? A simple impairment test should suffice.

  • This says .5ng/ml is way low and a bad way to do is by single blood test like the law hb13-1114 is proposing. Think of how much this will cost Colorado to defend vs. what is in the bill for costs. Washington State is having a huge problem with this level and legal premise.


    DOT HS 808 078 NOVEMBER 1993.



    In summary, this program of research has shown that
    marijuana, when taken alone, produces a moderate degree of driving impairment
    which is related to the consumed THC dose. The impairment manifests itself
    mainly in the ability to maintain a steady lateral position on the road, but
    its magnitude is not exceptional in comparison with changes produced by many
    medicinal drugs and alcohol. Drivers under the influence of marijuana retain
    insight in their performance and will compensate where they can, for example,
    by slowing down or increasing effort. As a consequence, THC’s adverse effects
    on driving performance appear relatively small. Still we can easily imagine
    situations where the influence of marijuana smoking might have an exceedingly
    dangerous effect; i.e., emergency situations which put high demands on the
    driver’s information processing capacity, prolonged monotonous driving, and
    after THC has been taken with other drugs, especially alcohol. We therefore
    agree with Moskowitz’ conclusion that “any situation in which safety both
    for self and others depends upon alertness and capability of control of
    man-machine interaction precludes the use of marijuana”. However, the
    magnitude of marijuana’s, relative to many other drugs’, effects also justify
    Gieringer’s (1988) conclusion that “marijuana impairment presents a real,
    but secondary, safety risk; and that alcohol is the leading drug-related
    accident risk factor”. Of the many psychotropic drugs, licit and illicit,
    that are available and used by people who subsequently drive, marijuana may
    well be among the least harmful. Campaigns to discourage the use of marijuana
    by drivers are certainly warranted. But concentrating a campaign on marijuana
    alone may not be in proportion to the safety problem it causes.


    One of the program’s objectives was to determine
    whether it is possible to predict driving impairment by plasma concentrations
    of THC and/or its metabolite, THC-COOH, in single samples. The answer is very
    clear: it is not. Plasma of drivers showing substantial impairment in these
    studies contained both high and low THC concentrations; and, drivers with high
    plasma concentrations showed substantial, but also no impairment, or even some
    improvement. The first driving study showed that impairment in the road
    tracking test was nearly the same in the first and second test, executed
    between 40-60 and 100-120 minutes after initiation of smoking, respectively.
    Plasma concentrations of THC and THC-COOH, however, were not the same during
    the tests: both were lower during the second than the first. The same pattern
    was found for ratings of perceived “high”. It has been said that
    behavioral signs of intoxication, though small, outlast physiological and
    subjective reactions to THC (Reeve et al. 1983; Yesavage et al., 1985). to
    examine this hypothesis, future research should extend actual driving
    performance measurements to 4, 8, 16 and 24 hours after smoking. If driving
    impairment still occurs after THC disappears from plasma, it could mean that
    previous epidemiological research has underestimated the proportion of drivers
    who were driving under the influence of marijuana at the times their accidents

    Mean speed was the only measure of driving
    performance that was even moderately related to plasma concentrations of the
    drug. Subjects with higher THC concentrations in plasma drove slower in the
    standard road tracking test (correlations varying from r = -.18 to r = -.72
    between conditions). This effect might have been even more pronounced if the
    subjects had not been instructed to drive at a particular speed, and if they
    had had no feedback from the speedometer.


    The major conclusions from the present program are
    summarized as follows:

    * Current users of marijuana prefer THC doses of
    about 300 ug/kg to achieve their desired “high”.

    * It is possible to safely study the effects of
    marijuana on driving on highways or city streets in the presence of other

    * Marijuana smoking impairs fundamental road
    tracking ability with the degree if impairment increasing as a function of the
    consumed THC dose.

    * Marijuana smoking which delivers THC up to a 300
    ug/kg dose slightly impairs the ability to maintain a constant headway while
    following another car.

    * A low THC dose (100 ug/kg) does not impair driving
    ability in urban traffic to the same extent as a blood alcohol concentration
    (BAC) of 0.04g%.

    * Drivers under the influence of marijuana tend to
    over-estimate the adverse effects of the drug on their driving quality and
    compensate when they can; e.g. by increasing effort to accomplish the task,
    increasing headway or slowing down, or a combination of these.

    * Drivers under the influence of alcohol tend to
    under-estimate the adverse effects of the drug on their driving quality and do
    not invest compensatory effort.

    * The maximum road tracking impairment after the highest
    THC dose (300 ug/kg) was within a range of effects produced by many commonly
    used medicinal drugs and less than that associated with a blood alcohol
    concentration (BAC) of 0.08g% in previous studies employing the same test.

    * It is not possible to conclude anything about a
    driver’s impairment on the basis of his/her plasma concentrations of THC and
    THC-COOH determined in a single sample.

  • Thank Aurora Sentinel for object coverage of this bill – too many Democrats at the House think a limit is needed without any substantive evidence to support a low threshold. Having been a part of defeating this bill for the last two years, I appreciate the demand for science behind this standard instead of sensationalism.

    Lets not forget that we’ve had cannabis and cars in our society for over 50 years and that fatal car accidents have been on the DECLINE since MMJ laws came into effect. This bill threatens to leverage police and prosecutor powers to target patients and other adults without proper determination of impairment.

  • M. Walker

    Thank you for being a voice of reason about these policies. They follow the well-worn path of policies based on “moral panic.” Voices like yours help to reveal them for what they are–hugely flawed and unscientific.

  • Douglas

    we will hope science and logic prevail I did roofing by reefer ,about a thousand roofs…never fell what is the real issue

  • Thank you Aurora Sentinel! Drill down into the convoluted HB13-1114 and you’ll find that, if you’re one of the 12 of 6,000 who go to Court (from the fiscal note) on the misdemeanor charge of DUI, DWAI, or UDD, your accuser no longer has to come to Court to bear witness, a clear infringement on Amendment VI, US Constitution. From HB13-1114: ((2)(b) In any prosecution for the offense of DUI per se..the trier of fact (the jury) is allowed to infer the tests were defective or inaccurate (with evidence).. for impeachment of the analysis of the person’s blood or breath.