Should New Zealand Decriminalize Driving After Cannabis Consumption?

January 08 2020 – Guest Blogger

Should New Zealand Decriminalize Driving After Cannabis Consumption?
Should New Zealand Decriminalize Driving After Cannabis Consumption?

Guest blogger Trismegistus takes a look at the evidence and finds it indicates no basis for criminalizing drivers with THC in their bloodstream.


A year or two ago I was strolling through a shopping mall somewhere in New Zealand, when I noticed an ad pop up on an electronic billboard. It was a public safety reminder from our transport agency about the perils of mixing cannabis with driving. The image showed a car that had apparently fallen straight out of the sky and hit the road nose first. The poor driver must have been pretty damned high to have pulled that off.


The implication was clear enough, stoned drivers are much too far removed from reality to be able to drive safely. Big bold letters claimed that a driver on cannabis was twice as likely to be involved in a fatal crash. This immediately struck me as being odd. ‘Double the risk’ might impress the less statistically savvy, but my first thought was, “Twice? That’s not very much.” I found online literature from our transport agency earnestly warning people not to listen to anyone trying to doubt the danger by pointing out that, “Recent studies show drivers with cannabis (and no other substances) in their systems were almost twice as likely to be blamed for their fatal car crash than unimpaired drivers. ” The studies are not cited, but we are left to assume that this is the most damning piece of evidence against stoned driving they could find at the time since it was chosen for for the ad.


I had a wee look around for studies about other risk factors for driving. This Ministry of Transport document states that a driver aged 20-24 is three to four times more likely to crash. And this study found that drinking a non-alcoholic drink while driving increased the risk by 1.8 times. Thus evidence exists to suggest that cannabis being twice as likely to be involved in a crash makes it about as dangerous as drinking water while driving, and less dangerous than driving while being 24 years old. Aren’t statistics great?


But more telling is that here another NZ government department has a graph showing that a driver aged 20-29 with the current legally allowed blood alcohol concentration is nearly 20 times more likely to have a fatal crash. ActionPoint states explicitly that, “In New Zealand, drivers aged 20-29 with a BAC of 0.05mg/100ml are about 17 times more likely to be involved in a fatal crash than their sober counterpart.” A 17x risk from alcohol is legally allowed, but a 2x risk from cannabis is not?


Official guidelines recommend one or two standard drinks per hour to remain under the blood alcohol limit. If cannabis has only one eigth as much risk, as officially endorsed studies suggest, then that makes cannabis about as dangerous as one eigth to one quarter of one standard drink. Roughly 60ml of beer.


The ‘twice as likely’ claim is no longer seen on similar ads. These days the prefered line is that “1 in 4 drivers who crash and die are affected by cannabis”. This claim appears to be based on this study, which also contains gems like, “In terms of crash risk, most studies find odds ratios (ORs) of around 2 for cannabis alone,” and “With regard to the role of cannabis in crash responsibility, the majority of studies have failed to find ORs significantly different from 1 for cannabis alone.” An OR of 2 means double the risk and 1 means no difference. A study of fatally injured drivers is quoted:


In a more recent study, blood samples from 1,046 fatally injured New Zealand drivers were examined and it was found that almost half (48%) contained alcohol or other drugs (eg 30% had cannabis). In most cases the level of alcohol was above the legal limit, and 54% of those who had been drinking had also taken other impairing substances. Overall a greater proportion of fatally injured drivers had taken alcohol and cannabis in combination (14%) compared with either substance alone (alcohol 13%; cannabis 9%).


The devil is in the always in the detail. First off it is not stated whether the drivers were at fault or not. Secondly as you can see only 9% of the fatally injured drivers had cannabis in their system alone. So most of the ‘one in four’ drivers that the ad is referencing had alcohol or other drugs in their system as well. This makes it very difficult to draw any conclusions at all about whether cannabis was the main culprit.


And what does “affected by cannabis” mean? Too often in these kinds of studies it simply means that THC was found to be present in the blood stream. But as we know, cannabis can be thus detected for weeks after taking the drug, while the supposedly driving-impairing high (60ml of beer folks), lasts only two to three hours. Consider that one in six New Zealanders aged 15-64 defined themselves as ‘regular users’ of cannabis in a recent survey. A regular user, (depending on how that is defined), is likely to have THC in their blood stream constantly. One in six of us will test positive for cannabis at all times. Therefore the significance of “1 in 4 drivers who crash and die are affected by cannabis” starts to look very slim indeed. At the very least the fact of THC remaining in the system for so long reduces such claims to meaninglessness.


Consider also, that this statistic relates only to members of the population who crashed and died in cars. But the vast majority of people do not crash and die in cars. Therefore this statistic tells us nothing about the general population of drivers. It might be objected that even so, 1 in 4 seems disproportionately high. And even I find it hard to believe that 1 in 6 New Zealanders are regular smokers. However a greater proportion of fatally injured drivers having THC in their systems might simply be a reflection the type of person who is more likely to have a fatal car crash. They are more likely to be younger - younger people are more likely to smoke weed. They are more likely to be risk-takers, irresponsible, or flout the law - these people are surely more likely to do illegal drugs, the most common of which is cannabis. In other words it may well be that the type of person who is more likely to be killed in a car crash, happens to be the type of person who is more likely to smoke.


Maybe people who are into putting “bad boy” stickers and tinted windows on their cars boy-racer style are also more statistically likely have a fatal crash. If so would that mean that “bad boy” stickers and tinted windows are dangerous for driving? Of course not, stickers and tints don’t cause crashes, bad driving does. But that is the same logic on display in the ad. Correlation might be interesting, but it is not proof of causation.


Or the statistic might come from this report containing, “Analysis of the blood samples of drivers killed in crashes between January 2013 and May 2018...” Which found, “29 percent had used alcohol  27 percent had used cannabis  10 percent had used methamphetamine  15 percent had used other drugsAll of my above objections would still apply. This report does not even bother to say how many had used cannabis alone - a footnote blithely states, “Drivers may have used more than one of the identified drugs.” Which, again, makes the numbers a bit useless for drawing any inferences about cannabis. Odd then, that a government department saw fit to use the numbers to push inferences about cannabis onto the public anyway. But of course, state or corporate sponsored anti-cannabis propaganda has a history that goes back to the days when cannabis was supposedly causing people to chop up their familes with axes, jump out of windows, turn into frantic compulsive rapists, and, “This marijuana causes white women to seek sexual relations with Negroes, entertainers and any others.” Quelle horreur!


In the end this statistic held up to scare us off smoking and driving tells us nothing about whether or not smoking actually contributed to the crashes. The paucity of available evidence against against cannabis and driving is on display on a billboard.


Time and time again we see news items about cannabis and driving take the tone that it is a problem that we need to fix with more and better roadside testing and/or tougher penalties. Statistics are pulled out to show that not only are large numbers of people driving after smoking weed, but that a good percentage of them don’t even see a problem. The question of whether or not they might be right never seems to come up. Instead it’s just assumed that the silly weed smokers must have obviously had their judgement clouded by their chosen poison, and gosh what are we going to do about it. Its a special kind of logic where the people who don’t drive while high think that they probably know more about driving while high than the people who do drive while high. 


Here’s a good one:


Drug Foundation chief executive Ross Bell said many New Zealanders have bought into a "mythology" that driving high was safe, because they often drove more slowly. "Back in the 60s or 70s, people used to say they drove better drunk. It's that same argument."


The NZ Drug Foundation has an excellent website with great information and advice, but the argument here is that if that now out-of-date public attitude about drinking and driving was wrong, then it’s probably wrong for cannabis and driving too. No doubt this resonates with readers of a certain generation. But this is just plain old wonky inductive reasoning. It turns out that alcohol and cannabis are quite different things. Alcohol is known to seriously impair motor function and coordination, while boosting the ego and confidence, and leads us to make ill-considered snap decisions. This is clearly a nightmare combination of effects for driving a car, but cannabis does none of those things. (I’ve heard of plenty of smokers who liked to get high and do physical activity - extreme sports, martial arts, etc. Similar for alcohol? Not so much - that would be completely insane.) But lets not base our decision on our own personal biases on either side. Let’s take a look at the evidence.


What does the science actually say? Research about alcohol and driving is clear cut and simple: the more you drink, the more you crash. As noted above, there is no ‘safe’ lower level. But regarding cannabis interpreting the research is a minefield. How to measure driving impairment? Does it correlate to THC levels in the blood? Does the pot smoking experience level of the driver matter? If so what is a regular user? What level of effect on driving is significant enough for us to be worried about? Different studies answer these questions in different and utterly arbitrary ways. This creates a major headache for trying to understand the research and to compare results across studies. Takeaway, bullet point headlines such as those mentioned above, must be scrutinized by looking hard at the methodology and definitions in the relevant studies.


Having had a close look at numerous studies with conflicting conclusions, I can report that this is not a small problem. It’s possible for people on both sides of the argument to cherry pick studies that support their case somehow or other. All manner of misleading statistics can be conjured from such a situation and tossed into the spin-swamp of modern life.  My own ’60ml of beer’ line qualifies as such, it’s a reductionist claim meant only to highlight the very low level of  relative risk as described in NZ government literature. But ‘60ml of beer’ is helps us very little for describing the difference in risk between a driver who has had one puff of weed, and a driver who has just finished an hour-long spotting sesh.


Having said that, the basic question is simple: do THC levels in the blood correlate to impairment as relates to unsafe driving? There are two obvious places to start, studies that test stoned subjects in driving tests or simulations, and studies that report crash statistics where data is available about the THC levels of the drivers.


Simulations and driving tests do not produce any greatly concerning results for the safety of cannabis and driving. Those that conclude that cannabis does cause some driving impairment usually offer little on the significance of the effect. Typically on the negative side researchers note that stoned drivers have decreased reaction times, and are thus not as good at reacting to unexpected driving events. There are also suggestions that they don’t do as well at maintaining position while driving in a lane. Some tests however observe neither of these problems, “Reaction time and all other measures of driving performance remained unaffected.” In the studies that do find these negatives, it is almost always noted that their stoned driving subjects seem to be aware of these issues, and compensate accordingly by driving more slowly, more cautiously, with more intense concentration, and by increasing following distances. (Notice that this is completely opposite to the drunk driver, who is prone to over-confidence and underestimating impairment.) The authors often admit that by and large this compensation strategy seems to be effective - the negatives are cancelled out by extra-cautious driving. Here’s an example:


“Detrimental effects of cannabis use vary in a dose-related fashion, and are more pronounced with highly automatic driving functions than with more complex tasks that require conscious control, whereas with alcohol produces an opposite pattern of impairment. Because of both this and an increased awareness that they are impaired, marijuana smokers tend to compensate effectively while driving by utilizing a variety of behavioral strategies.”


Here’s another, “Drivers under the influence of marijuana retain insight in their performance and will compensate when they can, for example, by slowing down or increasing effort. As a consequence, THC’s adverse effects on driving performance appear relatively small.” And another, “Evidence from the present and previous studies strongly suggests that alcohol encourages risky driving whereas THC encourages greater caution, at least in experiments. Another way THC seems to differ qualitatively from many other drugs is that the former users seem better able to compensate for its adverse effects while driving under the influence.” The ‘myth’ of the stoned driver being ok by slowing down and concentrating is in fact a repeatedly scientifically observed phenomenon.


Of course, simulations and tests are one thing, real world driving on the road is another. The true battle ground for both sides of the debate is crash statistics. In a spasm of sanity several US states have legalized cannabis years ago. (Many. Years. Ago.) This study looked at fatal crashes in Colorado and Washington state and concluded that “Three years after recreational marijuana legalization, changes in motor vehicle crash fatality rates for Washington and Colorado were not statistically different from those in similar states without recreational marijuana legalization.” Insurance claim data often shows a small increase in minor accidents however, which makes sense since cannabis clearly does cause some minor driving impairment, like drinking bottled water and other things that we don’t criminalize people for.


This culpability meta-analysis (statistical analysis of a group of studies), looked for a relationship between THC-positive drivers and who was at fault in a crash, concluding, “Culpability Ors exaggerate risk increases and parameter uncertainty when misinterpreted as total crash Ors The increased crash risk associated with THC-positive drivers in culpability studies is low.” And this culpability study looked at blood samples from 2,500 injured drivers and found that, “There was a clear relationship between alcohol and culpability. … In contrast, there was no significant increase in culpability for cannabinoids alone. While a relatively large number of injured drivers tested positive for cannabinoids, culpability rates were no higher than those for the drug free group. This is consistent with other findings.”


This study even dared to suggest that legalizing cannabis medicinally might even lower traffic fatalities. No one is trying to claim that cannabis makes one a better driver. Rather it might be, for example, that some people have switched from using the outstandingly dangerous ethanol named alcohol, to the not much dangerous cannabis.


Since 1996, 28 states have legalized marijuana for medical use. Deaths dropped 11 percent on average in states that legalized medical marijuana, researchers discovered after analyzing 1.2 million traffic fatalities nationwide from 1985 through 2014. The decrease in traffic fatalities was particularly striking – 12 percent – in 25- to 44-year-olds, an age group with a large percentage of registered medical marijuana users... the results mirror the findings of another study of data from 19 states published in 2013 in The Journal of Law and Economics. It showed an 8 to 11 percent decrease in traffic fatalities during the first full year after legalization of medical marijuana. “Public safety doesn’t decrease with increased access to marijuana, rather it improves,” Benjamin Hansen, one of the authors of the previous study, said in an email.


Yes friends, there is evidence that anyone campaigning against legalization is working against public safety on our roads. 1.2 million is quite a decent sample size is it not?


In the driving section of a prominent NZ anti-cannabis website, the first piece of offered evidence is a study claiming that, ”habitual users of marijuana have about 10 times the risk of car crash injury or death compared to infrequent or non-users.” ‘Habitual user’ was defined in the study as someone who smokes once per week or more, a rather broad definition which could include extreme all day bong hit artists. The sample size was only 57. 10x grabs the attention a bit more than 2x for sure, but recall that the risk multiplier for a driver at the legally allowed blood alcohol concentration is 17x. What I learned from this study, was that even the most hideous weed monsters among us, are still less dangerous drivers than someone who has had one or two standard drinks of alcohol. The website declines to mention that the same study also looked for a link between crashes and “acute use” of cannabis, i.e. where drivers had smoked less than three hours before crashing. After adjusting for confounders like alcohol, they found that acute users had less crashes (OR = 0.8), although this result was not statistically significant. In other words, the authors found no link at all between driving stoned and crashing more. Instead they ended up performing a statistical analysis to determine whether stoned drivers crashing less was significant, since that’s what they observed.


There is another major problem for the criminalization of driving on cannabis. There is positive evidence that the measured level of THC in the blood is simply not a reliable indicator of driving impairment. Any chosen cut-off  for conviction is hopelessly arbitrary. The strength of reactions to THC vary greatly by individual and by experience, one size does not fit all. In 2016 the AAA Foundation for Traffic Safety commissioned a study which concluded, “Based on this analysis, a quantitative threshold for per se laws for THC following cannabis use cannot be scientifically supported.” [Their emphasis.] If there is no scientific basis for THC levels being a reliable measure for driving impairment, then what will the state use as evidence to obtain a conviction in a court of law? Stand on one foot and touch your nose? Please... More research that supports this conclusion could see the state’s case for arresting stoned drivers collapse completely. Yet another example of the uselessness of trying to shove cannabis into an alcohol shaped box.


Every now and then there is some awful tragic accident where the culprit tests positive for cannabis. I don’t really blame any grieving family members for concluding that ‘drug driving’ is a problem. It’s human to seek an explanation when such a thing happens, and when the blood test says ‘cannabis’ I imagine it’s also human to think you’ve found it. But correlation is not causation. Drinking and driving is a black and white thing, easy to understand. Cannabis and driving is tricky, complicated, and not easy to understand.


Let me be very clear: I’m not giving anyone the green light to smoke and drive without fear. I’m not trying to pretend there is no risk - there is risk. Smoking and driving should be actively discouraged. I’m saying it’s long past time to cut through the hysteria and scaremongering: it’s time to get real about the relative risk of cannabis and driving.


If the state wants to wreck people’s lives with a criminal conviction for a supposed offence, then surely the onus is on the state to prove their case. The status quo seems to be, “We’re not sure what to do about cannabis and driving, so while we’re waiting for evidence that suits us, even though the question has been studied for many years, better safe than sorry, we’re going to wreck your life anyway.” Guilty until proven innocent. Well, just ‘guilty’ actually. The NZ government consistently claims to make laws based on evidence. Yet regarding the danger of cannabis and driving they offer only weak, easily debunked junk statistics.


There is simply not enough evidence of a public safety concern for the state to justify a criminal conviction for driving while being a pot smoker. There’s not even enough evidence to suggest that driving straight after smoking is a serious concern. Also there does not seem to be any good way to equate THC levels in the blood with driving impairment, which is the one and only evidential requirement in a court of law. And the reason for these things is not a lack of research, instead the research indicates that the big bad danger simply isn’t there.


There is no justification for a ‘drugged driving’ conviction for cannabis. There is no need for tougher laws and penalties. There is no need for roadside drug tests. Instead police should put more resources into the obvious, well known, and well scientifically documented problem of drinking and driving.


All that is required is a good awareness campaign with some decent advice:


    • When you smoke plan to not drive for at least three hours.
    • If the need arises use your own judgement about whether or not to drive. This is a problem for drunk persons, but not for stoned persons - no matter what your sensitivity or level of experience with cannabis, if you’re too high to drive, you’ll know it. When in doubt - don’t.
    • If you do drive - concentrate, be aware of a slightly lessened reaction time, slow down, don’t overtake, increase your following distances, double check your decisions at intersections, avoid distractions.
    • Never drive after mixing cannabis with alcohol. There is evidence to suggest that the combination is worse for driving than either drug alone. But you already knew not to drink and drive anyway right?


Every now and then a NZ politician is asked why our cannabis laws are stuck in a time warp while the rest of the world is moving on. Mostly I think they are afraid that softening the laws as much as they should be softened won’t go down well with their voter base. That, and they don’t much fancy listening to their political opponents howling “Show us your bong!” ad nauseum. But the line of reply that amuses me is, “Well, we don’t want to send the wrong message to our young folk.” Yes, think of the children. I’ve got news for anyone who believes that. Today’s younger generation has grown up with a thing called the internet and they’re not as dumb as you think. Witness the fact that they are going on strike over climate change.

They’re also quite capable of figuring out that our cannabis laws are based on a hangover from decades of deliberate reefer madness propaganda, and Richard Nixon’s attempt to attack the hippies for being so insolent as to protest his precious war in Vietnam. One of Nixon’s top advisors John Erlichman admitted the truth in a 1994 interview:


"You understand what I'm saying? We knew we couldn't make it illegal to be either against the war or black, but by getting the public to associate the hippies with marijuana and blacks with heroin. And then criminalizing both heavily, we could disrupt those communities," Ehrlichman said. "We could arrest their leaders. raid their homes, break up their meetings, and vilify them night after night on the evening news. Did we know we were lying about the drugs? Of course we did."



Nixon was a paranoid ideologue, who believed that the rise of cannabis was a lefty communist plot to destroy minds, thus the lies to the public were justified in his mind by the greater good. Science? Public health and safety? Evidence based? Not so much. Nixon’s war on drugs turned out to be a war on drug users. He commissioned a report on the dangers of cannabis after realizing that no hard evidence of such existed, and then tried to stop its conclusion being presented because the conclusion was the same as all other similar subsequent reports around the globe: decriminalize. The USA then placed pressure on other nations to conform to their lying vision of drug policy, (because you do what ya gotta do to stop a lefty commie plot now don’t-cha). In NZ these lies manifested as The Misuse of Drugs Act 1975 which, incredibly,  informs our drug policy to this day.


It might be in some politicians’ own interest, if they began to realize that the message that our current cannabis laws send to the younger generation is that the people who occupy The Beehive clearly do not work in the interests of  the people. They are willing to throw a percentage of their citizens on the scrapheap for no good reason at all, just because they feel a need to appease and reinforce an ignorant and biased glow of manufactured moral superiority and disapproval for certain voters. Great work thanks for that. And why should young people respect the police, who enforce these unjust laws? This is the message we are sending to our next generation. New Zealand is dragging it’s heels on cannabis law reform against all evidence because it works for the careers of certain politicians.


As far as I can tell NZ has no chosen THC level for a drugged driving conviction. All that is required is the mere presence of THC in the blood. It is unfortunately illegal in New Zealand to possess cannabis, but it is not illegal to be a person who smoked cannabis last week. Until you drive a car, then it suddenly is illegal to have smoked last week. Lives are being wrecked over this ridiculousness.


Given that THC can remain detectable for weeks after the relatively minor impairment has worn off, this effectively means that our current laws are persecuting pot smokers. Just as Nixon intended. Criminalizing them with spurious and moralizing reasons while ignoring the evidence. Just like Nixon did.


Stop criminalizing people who neither deserve nor need to be criminalized. You’ll sleep better.

And we could all use one less official bogeyman if that’s alright.


This article was written by our guest blogger: Trismegistus.

Trismegistus is a philosopher, musician, writer, and psychonaut.

Sometimes guest writers contribute to our blog here at MindFuel. These writers come from a wide range of backgrounds and experiences, making their knowledge invaluable. Read more about our writers.

See also: Study on driving and cannabis finds CBD alone doesn't impair driving ability.

1 comment

  • Tim: November 06, 2019
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