By on December 14, 2015


Puff, puff, pass that bill. Federal authorities want to know how stoned is too stoned for drivers, according to a provision in the recently signed Federal Highways Bill.

The new law directs U.S. Department of Transportation Secretary Anthony Foxx to study the effects of marijuana on drivers and present those findings to Congress by the end of 2016.

As more states legalize marijuana — Oregon and Alaska joined Washington and Colorado with legal pot, and 12 states have decriminalized possession — Congress asked the department to determine how to train police to spot stoned drivers and how to test them.

According to a Gallup Poll this year, 47 percent of American surveyed said they thought marijuana would make the roads less safe in states with legalized cannabis.

Authorities in Colorado initially struggled with how to test drivers and measure levels of THC in their systems. Colorado’s threshold of 5 nanograms of THC to qualify as “too stoned to drive” was met with opposition in 2012. Medical marijuana proponents said the per se limit was too low, but the limit was passed into law anyway.

Interestingly, Westword’s pot critic in Denver, William Breathes, had a resting THC level three-times the legal limit the newspaper discovered in 2013.

This year, the University of Iowa discovered that the marijuana equivalent for 0.08 blood-alcohol content (the legal limit for drunk driving in many states) is roughly 13 nanograms of THC. But marijuana and alcohol are very different drugs. Marijuana lasts far longer in users’ blood streams and is difficult to metabolize.

“Everyone wants a Breathalyzer which works for alcohol because alcohol is metabolized in the lungs,” Andrew Spurgin, a postdoctoral research fellow with the UI College of Pharmacy said in a statement announcing the results. “But for cannabis this isn’t as simple due to THC’s metabolic and chemical properties.”

Nonetheless, the feds want to know how stoned is too stoned, and how many stoned drivers are drunk too. (Anecdotally: Many Denver police officers say that they issue more DUI and driving while stoned tickets at the same time than they issue drugged driving tickets alone.)

It looks like the feds just got a lot of money to find out.

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32 Comments on “How Stoned is Too Stoned to Drive? The Feds Want To Know...”

  • avatar

    “The new law directs U.S. Department of Transportation Secretary Anthony Foxx to study the effects of marijuana on drivers and present those findings to Congress by the end of 2016.”


    Seems like being Secretary of Transportation, would be the dream of every stoner!

  • avatar

    Oh wow man. I forgot what I was going to say.

  • avatar

    By the way, given the knuckle headed thinking in DC these days, I would propose this headline for a companion article:

    “How Stoned is Too Stoned to Drive? The Feds Ought To Know…”

  • avatar
    George B

    It’s likely we could create a reaction time test, but the results would be inconvenient. My elderly parents appear to have relatively poor reaction time and they haven’t been intoxicated in more than a decade. To their credit, my parents know their limitations and avoid difficult driving conditions.

  • avatar

    Is it really an issue since in the states that have legalized marijuana accidents have gone down?

    • 0 avatar

      You keep making excellent comments.

      I’ve got to look this one up.

      • 0 avatar



        I think the biggest reason is that if people are getting stoned on marijuana, they might be less likely to drink. Every study seams to suggest that drinking impairs driving more than marijuana. Obviously I wouldn’t condone either and driving.

        • 0 avatar

          Thanks for the links. I absolutely would rather have a road full of stoners than of drunks.

          And not just because I’m an alumnus. They’re already getting all the rush they need between their ears and don’t need one from their car.

          Dazed and confused, maybe, but at much lower speeds.

        • 0 avatar

          “I think the biggest reason is that if people are getting stoned on marijuana, they might be less likely to drink.”

          I would think that it’s more likely that MJ doesn’t make people as aggressive as alcohol does.

          • 0 avatar

            Your chances of being taken off the road due to an unexpected lengthy romantic encounter are greatly improved if you have a sufficient supply of high quality marijuana. You’re not likely to travel until well after the height of the euphoric marijuana induced climax. One may not evacuate such an encounter until the effects have mostly or completely worn off. The male participants in particular may not even notice that the other gender has bigger shoes than he does until well after the effects have worn off, and, having so noticed may “shake off” the marijuana effects suddenly and with perfect clarity and sobriety hit the highway.

            Don’t ask me how I know these things. I just do.

  • avatar


    Why do we park on a driveway and drive on a parkway?

  • avatar

    A BAC limit of .08 means you are sober, so it stands to reason the THC equivalent will seem unreasonably low. Meanwhile, distracted driving is probably equivalent to a BAC of .30.

    • 0 avatar

      I’m not sure .08 mg/ml for a BAC indicates sobriety, it is simply the threshold of being legally intoxicated.

      Whats of particular interest is even at .08, lower than .10 of only fifteen years hence, is among the highest legal tolerances in the world:

    • 0 avatar

      I played around with one of those breathalyzers once when doing some soldering. It turns out that once I got over the initial buzz, my BAC was still above .08 and I was able to solder just fine and didn’t feel “drunk” or buzzed at all. I felt completely normal.

      Not that I would DND but in my anecdotal account, I would have been perfectly fine to drink and perfectly “drunk” too.

      • 0 avatar

        I remember when they changed from .10 to .08 and remarked at the time, it was all about the “business” of drunken driving. Seeing the chart the US, Canada, and Mexico are actually the most lenient in this regard which surprised me.

      • 0 avatar

        I remember testing a driving video game. After one drink, scores went up (though not any more than controls drinking coke. Presumably the extra practice helps). After the second, the scores went down. I haven’t a clue about the strength of the drinks, but I’m willing to bet they were stronger than the “offical drink”. (first BAC chart duckduckgo found).

    • 0 avatar

      In the US, .08 or higher = DUI.

      That does not mean that a BAC of less than .08 = not DUI. But at lower BACs, the state has a more difficult case to prove because it has a higher burden of proof, so such cases are uncommon.

  • avatar

    I wonder how a level test could possibly work as everyone knows plenty of drunks who mange just fine at BAC levels that would have me on the floor….

    THC is the same ~ I remember people dying from the stupid shit they did when stoned but many more who managed to drive, work , play music , write , on and on….

    The comments to this should be interesting to say the least .


  • avatar

    Based on experience gained back in my bad old days (ancient history by now), I suggest that driving stoned promotes less aggressive driving than driving drunk. Not that I recommend either, of course. If anything, a stoned driver tends to be over-cautious if not a bit paranoid, but of course this does not take into account impaired reaction times or a lessened ability for dealing with the unexpected.

  • avatar

    The key difference between driving stoned and driving drunk is that you don’t feel invincible when you’re high. On cannabis, you feel good, you may even feel great, but you are aware of your impairment. Alcohol on the other hand, gives you a sense of being able do just about anything.

    Drunk Driver – “I can drive just fine, maybe even better!”

    Stoned Driver – “I really shouldn’t be doing this, better slow down.”

    • 0 avatar

      Alcohol doesn’t have that affect on me…

      It just makes me sleepy, and it sometimes has a mildly relaxing effect. Drinking heavily just makes me sleepier and dries out my mouth. Getting drunk is a pretty meh experience for me.

      Im not a teetotaler. I enjoy flavorful craft beers instead of dessert sometimes, its just that the alcohol provodes a bite but is otherwise a mildly annoying inconvenience.

      I bet that alcohol hits different people in different ways. It sounds like its way more fun to be you!

  • avatar

    Since blood levels and the slow metabolic decay of THC in the body make any sort of parts/unit concentrations dodgy, how about a straight forward test of sensory motor coordination and reaction times. It is not confiscating some one’s blood, and it is an entirely documentable objective measurement. Alcohol and cannabis are two different paradigms. Apple and oranges. Too many people in their ignorance draw direct parallels between the two. It is clearly a case of comparing apples and oranges.
    I used to (quit it in the 80’s), and who still know plenty of people who do slide off into the woods while out skiing and get quite baked, and go right back out and ski bumps no problem. Think driving is demanding of sensory motor skills and instant judgements? Granted it does but if you don’t know what bump skiing is . . .search engines and online videos will show you.

    • 0 avatar

      One summer session in college I aced all my classes and set up a JIT cart-exchange system for the nursing wards in a new U of Iowa hospital wing while being perpetually baked as a haddock.

      Weed is different.

    • 0 avatar

      Have you skiied Montana ? Or Colorado ? or Vermont ? or New Jersey, for that matter ? Yup. I’ve seen some blazed characters rip off maneuvers I only wish I could on skis….

  • avatar

    Cyclists can smell the marijuana fumes from inside passing cars. Sometimes it seems like 20% of the passing cars have people smoking up inside them. Of course the cyclist won’t know if the driver is high, but a lot of them must be. Given that driving while high is so common, the lack of statistics to link this to lots of accidents, it always seemed to me that it was very possible stoned drivers have less accidents than sober drivers. I have seen claims that both support and refute this. Certainly the answer isn’t clear.

  • avatar
    healthy skeptic

    I would never drive either drunk or stoned.

    Drunk, my reflexes and coordination go, and I would probably drive more recklessly due to lack of inhibition.

    Stoned, I just can’t concentrate. My mind wanders badly. I could see myself cruising serenely right through a red light.

  • avatar

    Instead of spending $50 million in typical Federal government fashion to seek obvious answers to stupid questions, why not just recommend zero tolerance as a guideline to the states and be done with it? Anything more than that is splitting hairs and is an unnecessary cost to the US taxpayer (albeit, a water molecule in a 5-gallon bucket, but still. It’s waste).

    Go ahead, light up, I don’t care what you consume. It’s none of my business nor my concern what you put in your body. Just stay off of the roadway, and don’t expect the public to pick up the tab for your imminent drug-related health problems.

    This is another example of a state-level issue.

  • avatar

    “12 states have decriminalized possession”

    What does this mean, you just get a fine but not a ride in a police car?

  • avatar

    Decriminalization just means it is not a criminal code violation. One way to look at is a speeding ticket versus speeding causing death. There will be infractions but they won’t mean criminal court or a criminal record. Too many violations would mean a bump up to criminal court. Canada looked at decriminalization a long time ago but once Conservatives got elected the whole idea went up in smoke ;)

    With that being said, what constitutes an impairment threshold will also depend on which side of the political Isle (chasm) that you sit.

    The problem with testing for blood levels of marijuana is getting a person to a qualified lab and getting the blood work drawn and run. IIRC Marijuana has a fairly long serum 1/2 life so testing expediency might not be an issue but are you going to detain every suspect during the time it takes to confirm blood levels?

    Urine tests are cheap, quick and easy to administer but all they provide is a yes/no answer.

    THC tends to accumulate in adipose so i can see the court defense now….. my client is a former marijuana smoker who just went on a crash diet or the famous Canadian snowboarder who kept his Olympic Gold medal by claiming a failed test was due to “passive” 2nd hand smoke. (Aren’t all marijuana smokers passive? LOL)

    This will be an interesting legal maze to navigate.”

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