Study: Per Se Drugged Driving Laws Have Little Or No Impact On Traffic Deaths

The imposition of so-called per se drugged driving laws, which create new traffic safety violations for drivers who operate a vehicle with the presence of trace amounts of certain controlled substances and/or their inert metabolites (byproducts) in their blood or urine, do not reduce incidences of traffic safety deaths.

That’s the conclusion of a just-published study by economists at the University of Colorado, Denver and Montana State University. The study is available from the Institute for the Study of Labor (IZA) in Germany as a Discussion Paper.

Since 1990, 11 states have passed so-called zero-tolerant per se drugged driving laws which make it illegal for one to drive with detectable levels of a controlled substance in his or her system. Five additional states have passed similar laws specifying non-zero limits for controlled substances or their metabolites. Fourteen (Arizona, Delaware, Georgia, Illinois, Indiana, Iowa, Michigan, Nevada, Ohio, Pennsylvania, Rhode Island, Utah, Washington, and Wisconsin) of these sixteen states impose these strict liability per se standards for cannabis. Recently, the White House Office of National Drug Control has recommended zero tolerant per se drug standards for all US states.

Using state-level data from the Fatality Analysis Reporting System (FARS) for the period 1990-2010, authors examined the relationship between the adoption of controlled substance per se thresholds and overall incidences of traffic fatalities. They found that the relationship is statistically indistinguishable from zero and concluded that there is no evidence that these limits reduced traffic deaths.

Authors reported: “Despite the fact that these laws have been touted by politicians and academics as an effective strategy for making our roadways safer, we find no evidence that they reduce traffic fatalities. … [W]e cannot determine why per se drugged driving laws do not work, and leave this issue to future researchers. However, our results clearly indicate that, as currently implemented, laws that make it illegal to drive with detectable levels of a controlled substance in the system have little to no effect on traffic fatalities.”

In November, Washington state voters approved Initiative 502, which legalizes the private use and retail sale of cannabis to adults, but also imposes a 5ng/ml THC/blood per se limit for drivers over the age of 21. In Colorado, where voters on Election Day similarly legalized cannabis, Democrat Gov. John Hickenlooper and Republican Senator Steven King are calling for the passage of nearly identical per se cannabis legislation.

NORML has consistently opposed the imposition of stand-alone per se limits for cannabinoids, arguing that the presence of THC in blood, particularly at lower levels, is an inconsistent predictor of behavioral impairment, particularly in more frequent consumers who may potentially test positive for trace, residual THC levels in their blood for periods of time exceeding any period of acute impairment.

Operation of a motor vehicle while under the influence of cannabis is already a criminal offense in all 50 states. However, in order for one to gain a criminal conviction under most state DUI laws, prosecutors must prove that a motorist recently ingested cannabis and that doing so prohibited him or her from driving safely.

Full text of the study, “Per Se Drugged Driving Laws and Traffic Fatalities,” is available online here. A separate paper previously published by the same authors reported that the passage of statewide medical marijuana laws is associated with decreased incidences of traffic fatalities.

38 thoughts

  1. A responsible cannabis user does not support drugged driving.

    [Paul Armentano responds: Agreed, as per NORML’s Principles of Responsible Use:

    II. No Driving
    The responsible cannabis consumer does not operate a motor vehicle or other dangerous machinery while impaired by cannabis, nor (like other responsible citizens) while impaired by any other substance or condition, including some medicines and fatigue.

    Although cannabis is said by most experts to be safer than alcohol and many prescription drugs with motorists, responsible cannabis consumers never operate motor vehicles in an impaired condition. Public safety demands not only that impaired drivers be taken off the road, but that objective measures of impairment be developed and used, rather than chemical testing.]

  2. I keep saying this and I wish someone would seriously look into it:

    for the past 30+ years we’ve been doing an in vivo experiment concerning marijuana use and traffic safety and the results are in. It would appear that permitting marijuana use actually REDUCES incidents of traffic fatalities. Why? B/c drivers under the influence of mj tend to drive slower (not to the point of creating obstruction) and tend to leave more space between themselves and the vehicle ahead of them. also mj may tend to make drivers less aggressive.

    If you compare year by year mj-related laws with same year traffic safety statistics, you’ll find not only that there is no impact of decriminalization of marijuana or permission of medical use on traffic safety, except to lower incidents of traffic fatalities. Check it out for yourself and get back to me….somebody?

  3. Marijuana is safer…Any one want to try it on a moterbike? It’s not like driving a car you know. It takes skill and good judment to get a powerfull 750 cc. motorbike capable of a top speed that’s well over 100 miles an hour down the road without geting killed, just saying…

  4. ive never had a moving violation.been driving for almost 20 years. im stoned probably at least half the time,but i have a very high tolerance….

  5. I rode motorcycles for years and on many occasions have rode under the influence of cannabis and as long as your not an idiot to begin with its perfectly safe. I always rode slower and more cautiously after smoking but i do think its a better idea to drive or ride completely sober.

  6. I don’t think anyone with any sense supports someone driving any vehicle under the influence of cannabis. Cannabis is too special to not be responsible users! Do not drive! Plan ahead, work hard, stand up for what is right!!! I look forward to making this world a better place with you all!

  7. All studies I have read concluded that experienced smokers drove better while high.They couldn’t really say for the inexperienced ones none of them wanted to drive.

  8. I took my road test stoned in 1977. I am under the influence 99% of the time I am behind the wheel and have never caused an accident or been cited for DUI – EVEN WHEN I GOT BUSTED FOR POSSESSION AT A NJ TURNPIKE REST STOP!!!!!!

    Drug testing for weed is all a part of the “masterpiece in brainwashing” cannabis prohibition has become.


  9. That’s a little unfair, seeing as how marijuana is stored in the fat cells in your body, and can stay there for weeks, even months. There’s no accurate way of telling if someone is high or not.

    I, for example, do better on tests, stayed focus on one thing for longer periods of time, drive better, and can stay relaxed and more calm. Red eyes doesn’t prove that someone is high; just that they are either dehydrated, have severe allergies, or just eye irritation. And motor skills? Forget about it.

    There’s no way in Hell that someone can tell if someone else is high, just by looking at them, or a urine test.

  10. I went to jail for six months, house arrest for 7-months, probation for 4 1/2 years, and lost my license at age 22 until im 29 1/2….. All because I was charged with two DUIs for cannabis within the same 48 hours – and was convicted of both regardless of over $40k in legal fees on a high powered attorney…… They never even took into consideration ONCE, the levels of THC present in my blood (less than 1ng/ml)..
    These laws need to change before more and more people like myself are tried, and have there lives turned upside down, because they smoked an L two weeks before getting pulled over…
    Fuck the pigs who arrested me and who continue to arrest innocent victims of the ongoing failed drug war on marijuana…

  11. Umm, I have driven tens of thousands of miles stoned as one can be. I don’t have crashes, I don’t get tickets and I do drive well. There is no correlation to having marijuana in your system and crappy driving. Texting, drinking, being otherwise distracted are what cause accidents. For most people being high makes them more aware.

    Now, if you’re a new driver and/or you do get jittery after smoking, then of course it is a very good idea not to drive to do anything else that might not be safe, like using a gun for target practice. Just play some games and relax.

    But my point is being stoned does not mean one cannot drive and the law must reflect this. Sure, after one fails to drive well, gets pulled over and fails a sobriety test, they should then be chemically tested to see why their condition is unfit and prosecuted as needed. But per se laws are, along with the assumption of being unfit to drive because of recent marijuana use, a sham.

  12. First off! They don’t care how many people die in car wrecks. If they did they would not let cars do 140 miles per hour. Where in America can you drive 140? They would shut them down at 75. But that would take to much money away from the fuzz in tickets and court costs. It would take money from the insurance company in lower rates. We have to keep those gas prices high as well.
    So I don’t even want to hear it!!!! Its all about the all mighty Dollar!!
    When the Gov can make more from legalizing weed than they do in court costs, fines and forfeitures it will be legal. Not one day before.

  13. This is something that depends on the person. Some people can drive safe while smoking marijuana others can’t. Instead of all this per se crap they should focus on people who drive dangerously regardless of what they are on. If you drive like a madman but are not on anything you get a fine but drive perfectly safe and happen to get caught driving high and you go straight to jail and get your license taken away. The law lets you drive as dangerous as you want as long as you are willing to pay for it and do it sober but no matter how safe you drive after smoking any amount of marijuana you go straight to jail. Does anyone see a problem with this?

    Also I have done some tests on this with some friends. We used the game Guitar Hero which takes an extreme amount of hand eye coordination and we were trying to get the best score in the world so we wanting to play at our best. There were 3 of us and we all played on expert we kept note of our scores while sober, drinking alcohol, and smoking marijuana. Surprisingly, all three of us consistently scored better while smoking marijuana. Alcohol was obviously the worst our scores started to go down even after 1 beer or less and continued to drop as alcohol consumption increased. My friend who is one of the best Guitar Hero players in the world got the highest score he has ever gotten on the hardest song in the game after smoking a pretty large amount of marijuana. He mainly smoked at my house so most of his play time has been at his house completely sober and he has not been able to reproduce that score even after several thousand tries. As a matter of fact all three of us got our best score on that song (Through the Fire and Flames) after smoking marijuana even though we have all played it hundreds of times sober. I would have never believed it unless I actually experienced it myself and I recommend more research be done on hand eye coordination and marijuana use. The only theory we could really come up with is marijuana seems to slightly slow down the speed of the games making the notes easier to hit and it also relaxes your muscles so you are not so tense while playing.
    I do not believe that it affects everyone like this as all people are different but it must be a substantial portion as it happened to all 3 of us. It also makes we wonder if marijuana use in musicians is actually helping them play better and help them relax while playing which makes you way less sore later. I know a lot of people will reject these ideas but I have seen no evidence that marijuana itself causes unsafe driving unless maybe you are ingesting some of the really strong concentrates and I still think the impairment is minimal even compared to a small amount of alcohol such as a beer or 2. The people that I have witnessed being unsafe drivers under the influence of marijuana where just generally reckless people no matter what substance they took but I don’t see anyone taking their license away.

  14. I agree with NORML, the responsible consumer does not drive stoned. And this is really only to make the public feel safe (and law enforcement’s job easier) in the newly emerging legal states when they have been told for decades by the government that marijuana is dangerous; and to protect inexperienced and moderate users and the public.

    The government has been pushing that marijuana causes impairment, they hide the difference between an inexperienced user compared to an experienced user. Lots of people get stoned and play video games or get stoned and go snowboarding without experiencing any form of impairment of their task. There is a huge difference the way marijuana effects the new or even moderate users compared to the way it effects someone who uses it everyday.

    To the inexperienced user and most moderate users, the marijuana high can be overwhelming to the consciousness and a person can experience mental and physical impairment. This is why the government can say that marijuana gives you memory loss and people lose control because they are only telling you half the truth. But a user who consumes or medicates everyday has become familiar with the stoned experience and can carry out any task with ease, probably even better because they have become better observers of reality.

    My research has found that the marijuana experience amplifies reality. That is why food tastes better, music sounds better, sex is better, etc. And the same thing is happening to your consciousness when you are under the effect. Your mind is kind of like a radio, it is receiving thoughts and broadcasting. To the inexperienced user they are caught off guard and confused by the often bizarre, funny, horrifying thoughts, that are amplified as part of the normal pulse/impulse consciousness. But these are normal thoughts nonetheless, just amplified, and can be strange to someone not familiar with an altered consciousness, that’s all.

    Now some people do not like marijuana because it amplify the truth; so people who tend to lie to themselves with usually say no to marijuana and choose alcohol. People who have a bad ‘trip’ on marijuana are not used to the bombardment of an amplified reality on their often limited, fantasy view of themselves and the world around them. So marijuana is indeed for the truthful, open-minded person.

    I like to use a surfing analogy to better explain the difference. There are many people who look at surfing and think it is impossible yet there are others who can easily do it. Before you learn how to surf you paddle out to the seemingly uncontrollable water that is thrashing you around; and when you try to catch a wave you get slammed underwater. At first the marijuana experience can seem bizarre and confusing and bewilder the user; and the high seems like your mind is being taken for a ride and you seem to lose all concentration. But eventually a surfer learns to catch the wave and take control of the water; just as the experienced user has taken control of the experience and uses it for pleasure, inspiration, spirituality, mental health, etc. I like to medicate and ride my bicycle or paddle my kayak. I can do this as well if not better than anyone who is ‘sober.’

    But for the respect of a legal marijuana framework of laws and responsibilities I support drug free driving.

  15. Yes, Jeedi, that is why these thing need to be explained clearly so people can make good decisions. In driving class, they should tell you not to smoke up and drive for the very reasons you mentioned, not some made-up-bullshit. I didn’t start smoking and driving until practicing both for a couple of years. At first, it just didn’t seem safe; someone that is drunk can not take accurate measure of how they feel while marijuana literally has the opposite effect.

    Anyway the numbers don’t lie, having marijuana in your system only increased the chance of an accident by 0.06 times. Having a cold and taking an over the counter med can increase that risk somewhere between 2 and 3 times. Being drunk is 3 to 8 times more likely to cause a crash.

    Effectively, there are more people fucked up on cold medications causing accidents right now. So why are we even hearing about the non-existant “dangerous of marijuana’ed driving”??? We need to focus on real problems, not stories.

  16. wbs 101 quote:

    “The only theory we could really come up with is marijuana seems to slightly slow down the speed of the games making the notes easier to hit and it also relaxes your muscles so you are not so tense while playing”.

    I think that has been observed in different ways from many cannabis users over the decades or centuries.Even in most textbook descriptions, describing marijuana impairment, excuse me,”enhancement”describe the sensation ‘of time slowing down’.

    I think a good description would be akin to sitting in a passenger side of a car and looking out the window at the landscape,when the car is doing 20 miles an hour,you can see detail,(individual houses,trees ect)the faster you go everything becomes more of a blur. This means you have more time to react within a situation(when time is slowed down) as opposed to going super fast and losing focus on the details until everything looks like a solid line

    This attribute of cannabis could apply to activities that require cordination such as a sport’s inhancement(getting into the zone) and enjoyment, as well as task that require creativity.
    or even critical thinking…I know this goes against the propoganda we have been taught,but in needs to be explored further.

    Think of all the artist,and musicians over the ages, lets say they all had to pass a piss -test to validate their works and skills…I bet a lot of musical recordings,performances,literature and artwork would never see the light of day.

  17. I dunno, it could be me, I’ve just never been high to the point where I felt impaired. Back in “the day” I had a toyota that I’d bought new and put 275000 miles on without a single accident or citation beyond speeding, which totalled maybe 3 over 12 years. When I had that toyota I was in a situation where I was smoking high quality weed pretty much on a daily basis. I don’t recall ever being incapable of driving well enough to comply with traffic signs and signals, or being unable to navigate traffic. Never been pulled over for questionable driving moves. Just has never happened.

  18. Studies have shown marijuana users are Safer Drivers than either drunk drivers, or sober ones.

    One study, entitled “Medical Marijuana Laws, Traffic Fatalities, and Alcohol Consumption” conducted in November 2011 provides evidence that marijuana is a safer substitute for alcohol when it comes to health and also makes for safer drivers.

    Top Ten Reasons Marijuana Users Are Safe Drivers

    When you combine all of the main results of these two decades worth of scientific research studies, the following 10 reasons marijuana drivers are safer than drunk drivers comes out like this:

    1. Drivers who had been using marijuana were found to drive slower, according to a 1983 study done by U.S. National Highway Transportation Safety Administration (NHTSA). This was seen as a factor in their favor, since drivers who drank alcohol usually drove faster and that is part of the reason they had accidents.

    2. Marijuana users were able to drive straight and not have any trouble staying in their own lanes when driving on the highway, according to a NHTSA done in 1993 in the Netherlands. The study determined also that the use of marijuana had very little effect on the person’s overall driving ability.

    3. Drivers who had smoked marijuana were shown to be less likely to try to pass other cars and to drive at a consistent speed, according to a University of Adelaide study done in Australia. The study showed no danger unless the drivers had also been drinking alcohol.

    4. Drivers high on marijuana were also shown to be less likely to drive in a reckless fashion, according to a study done in 2000 in the UK by the UK Transport Research Lab. The study was done using drivers on driving simulators over a period of a month and was actually undertaken to show that pot was a cause for impairment, but instead it showed the opposite and confirmed that these drivers were actually much safer than some of the other drivers on the road.

    5. States that allow the legal use of marijuana for medical reasons are noticing less traffic fatalities; for instance, in Colorado and Montana there has been a nine percent drop in traffic fatalities and a five percent drop in beer sales. The conclusion was that using marijuana actually has helped save lives. Medical marijuana is allowed in 16 states in the U.S.

    6. Low doses of marijuana in a person’s system was found by tests in Canada in 2002 to have little effect on a person’s ability to drive a car, and that these drivers were in much fewer car crashes than alcohol drinkers.

    7. Most marijuana smokers have fewer crashes because they don’t even drive in the first place and just stay home thus concluded more than one of these tests on pot smoking and driving.

    8. Marijuana smokers are thought to be more sober drivers. Traffic information from 13 states where medical marijuana is legal showed that these drivers were actually safer and more careful than many other drivers on the road. These studies were confirmed by the University of Colorado and the Montana State University when they compared a relationship between legal marijuana use and deaths in traffic accidents in those states. The studies done by a group called the Truth About Cars showed that traffic deaths fell nine percent in states with legal use of medical marijuana.

    9. Multiple studies showed that marijuana smokers were less likely to be risk takers than those that use alcohol. The studies showed that the marijuana calmed them down and made them actually pay more attention to their abilities. All of these tests and research studies showed that while some people think that marijuana is a major cause of traffic problems, in reality it may make the users even safer when they get behind the wheel.

    10. Marijuana smoking drivers were shown to drive at prescribed following distances, which made them less likely to cause or have crashes.

    .. stick *that* in your pipe, and smoke it!

  19. Is Driving High on Marijuana Safer Than Driving Drunk? [ or driving sober?!! ]
    For decades, marijuana advocates have argued that pot has a significantly different effect on driving ability than alcohol. But if you take the word of one auto insurance company, stoned is actually the safest way to drive. is making that case based on years’ worth of scientific studies, including some from the US National Highway Transportation Safety Administration that found motorists under the influence of marijuana tended to drive slower and have accident responsibility rates lower than those of drug-free drivers.

  20. A 2002 review of seven separate crash culpability studies involving 7,934 drivers reported, “Crash culpability studies [which attempt to correlate the responsibility of a driver for an accident to his or her consumption of a drug and the level of drug compound in his or her system] have failed to demonstrate that drivers with cannabinoids in the blood are significantly more likely than drug-free drivers to be culpable in road crashes.” [Chesher et al. Cannabis and alcohol in motor vehicle accidents. In: Grotenhermen and Russo (Eds) Cannabis and Cannabinoids: Pharmacology, Toxicology, and Therapeutic Potential. New York: Haworth Press. 2002: 313-323.]

    But, unlike with alcohol, the accident risk caused by cannabis, particularly among those who are not acutely intoxicated, appears limited because subjects under its influence are generally aware of their impairment and compensate to some extent, such as by slowing down and by focusing their attention when they know a response will be required. [Allison Smiley. Marijuana: On-Road and Driving Simulator Studies]

    This response is the opposite of that exhibited by drivers under the influence of alcohol, who tend to drive in a more risky manner proportional to their intoxication.[United Kingdom’s Advisory Council on the Misuse of Drugs. The Classification of Cannabis Under the Misuse of Drugs Act of 1971. 2002: See specifically: Chapter 4, Section 4.3.5: “Cannabis differs from alcohol; … it seems not to increase risk-taking behavior. This may explain why it appears to play a smaller role than alcohol in road traffic accidents.”]

  21. Cannabis use is associated with only marginal increases in traffic accident risk, comparable to anti-histamines and penicillin.

    An investigator from Aalborg University and the Institute of Transport Economics in Oslo assessed the risk of road accident associated with drivers’ use of licit and illicit drugs, including amphetamines, analgesics, anti-asthmatics, anti-depressives, anti-histamines, benzodiazepines, cannabis, cocaine, opiates, penicillin and zopiclone (a sleeping pill). His study reviewed data from 66 separate studies evaluating the use of illicit or prescribed drugs on accident risk; the study found that cannabis was associated with minor, but not significantly increased odds of traffic injury (1.06) or fatal accident (1.25). By comparison, opiates (1.44), benzodiazepine tranquillizers (2.30), anti-depressants (1.32), cocaine (2.96), amphetamines (4.46), and the sleeping aid zopiclone (2.60) were all associated with a greater risk of fatal accident than cannabis. Anti-histamines (1.12) and penicillin (1.12) were associated with comparable odds to cannabis.

  22. Oh dear oh dear oh dear ! Where do I begin with the flaws in this ? Here are a couple :

    1) The object was to achieve X. It did not achieve Y. Therefore it does not work ? At best “Ignoratio elenchi” !
    2) The “do not drive while blindfold” law did not reduce the number of deaths whiile driving. We conclude that there is no evidence that driving while blindfolded is dangerous. What are you guys on ?

    I think that you guys have been consuming far too much of your product, and as the REPUTABLE PEER REVIEWED research shows, regular consumption has both short AND long term affects on cognitive ability.

    I think that you have just provided significant additional evidence that it should NOT be legalised !

  23. Denis, get a clue please! If you’re doing something harmful, then why should you be punished for it? Drunk driving kills people. High driving doesn’t. The law needs to reflect what happens in the real world, not some subjective shitfest.

  24. Having just been in a verbal disagreement can make your driving worse than the strongest pot, because even your state of mind is stronger than marijuana’s effects on perception.

  25. Denis,c’mon… lighten up.It must be disturbing to know that cannabis does not effect you’re cognitive abilities and cordination in the same way alcohol does.The “reputable peers” that you have put your faith in,are not necessarily reputable, because they can easily be bought out to the highest bidder.And that has nothing to do with paranoia,just logic.

    But ill tell what is psychotic,the notion of a perfect future “drug free society” propoganda that started during the 80s.The people that are profiting on this notion,know that everything would change as far as their earnings and their corperate institutions,(if there was a drug free society),so they actualy are dependent on those “evil& misguided drug users for their livelihood.It has nothing to do with the innocent children that have their families torn apart by the “drug war,” because they need fresh new bodies to keep the dynamics going.

    Thank god people are waking up to this,but it also has to do with generational differences as well…Where talking about princeables like-honesty,values and morality.

  26. Well, Implementation of laws against drug driving seems to punish the law breakers, but its very unfortunate to see people play with their own lives and what laws are supposed to perform to prevent these deaths.

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