An issue with having the legal limit at ~2-5ng/ml is that it makes habitual users be over the limit if they have smoked recently or not.[0] Making the prohibition seem unserious to some, not about safety but about punitive control, and in turn making it matter less if you smoke and drive as you are taking the risk of getting into trouble in any case.
The impairments of driving under the influence of alcohol have been extensively studied, but unless I have overlooked the literature it seems that the same investigations have not been carried out with THC.
Since then, [0] has been published and I think it's worth at least a skim. Since it's quite recent the introduction summarizes some of the most recent research.
The things that jump out at me are:
- [0]: Habitual users with baseline concentrations above legal limits perform just as well as habitual users with baseline concentrations below the legal limit, indicating that for habitual users, the legal limit doesn't have any relation to impairement.
- [1]: A study in Canada analyzed crash reports and blood tests to look at the state of drivers responsible for accidents. While alcohol had a very clear and statistically-significant influence on the risk of a driver causing an accident, THC did not.
To steelman the idea that THC causes accidents, [0] only looks at habitual users with baseline levels of THC and [1] only looks at non-fatal injuries.
My conclusion right now is that the number of drivers in accidents with THC in their blood is going up because the number of people with THC in their blood is going up, not because drivers who use THC cause accidents.
The law's assumption that this level of THC is evidence of impairment seems to be invalid.
The law would be better off measuring impairment in some way and perhaps intensifying penalties when an impairment test fails and the user has THC concentration above some threshold.
> the number of drivers in accidents with THC in their blood is going up because the number of people with THC in their blood is going up
This.
In just the short time since legalization, recreational use in my immediate vicinity (a small Ohio village, one stop light) has decidedly, undeniably increased.
I offer only an anecdotal observation, but my evening walks around town are now accompanied by a dank potpourri of skunk scents, representing I-don't-know-how-many strains of Sativa...
Indica to me that at least 30% of the population here is puffing.
- [1]: A study in Canada analyzed crash reports and blood tests to look at the state of drivers responsible for accidents. While alcohol had a very clear and statistically-significant influence on the risk of a driver causing an accident, THC did not.
I don't understand how this study can make that claim just looking at crash report data. The assumption that not at fault drivers are representative of people who aren't in accidents at all is pretty generous? It seems likely that folks who are unimpaired are also better at avoiding accidents / driving defensively
My preferred way to wade through a political research topic like this is to look at the aviation industry. If a pilot can not use a medical substance, then it is very likely that there is some thing there. Pilots are generally fairly high investment, and they are also fairly international in research and standards. All nations with an airforce tend also be interested in such research, regardless of current political flavor.
"The results support our preliminary study and suggest that very complex human/machine performance can be impaired as long as 24h after smoking a moderate social dose of marijuana, and that the user may be unaware of the drug's influence. "
I’ve never been a smoker, but I’ve known a lot of friends who went through periods of smoking multiple times per week or even daily for periods of time.
Every single one of them denied impairment during those periods. Often vehemently so, belittling anyone who suggested they might be impaired as having succumbed to propaganda.
Every single one of them remarked that they were sharper, more alert, and had better memory after stopping.
It’s an interesting phenomenon to watch. I think it’s becoming more socially acceptable to acknowledge that marijuana causes impairment even after the obvious effects have subsided, which was a taboo topic in the years when saying anything negative about marijuana would get you attacked as being pro-prohibition or pro-imprisonment of drug users. I even remember one of the big technical forums in the 2010s had a long debate thread where people were claiming that THC made them better drivers and citing YouTube videos and “studies” to back it up. It would be rare to see anyone try to make that claim in today’s environment.
If you calmed down and stopped snapping at everyone, you might understand that I'm writing about how the law and a lack of studies could make some people more willing to drive high. You are substantially diminishing the quality of the discussion here.
The average (presumably arithmetic mean, though it could technically be any of a wide variety of measures) is not particulatly interesting, the median specifically would be more interesting, as a single figure.
This seems like an intentionally misleading title, since they don't mention that the study was for one county (Montgomery County) in Ohio, which is basically just Dayton, OH and surrounding rural area - < 600k people.
I'm sure you can pick other counties in the US which have either very high representation of THC users or very low representations. Without knowing how other counties score in terms of driver fatalities and THC, this is not really very useful.
To me it sounds like an effort to paint THC as big and scary. But in my experience living in a few large cities, weed is rare - but lots of people go out, drink, and drive home one or more times per week.
ScienceDaily goes even further by rounding up to 50% and burying the location halfway down the summarization.
"Nearly half of drivers killed in crashes had THC in their blood
THC-impaired driving deaths are soaring, and legalization hasn’t slowed the trend.
Date:
October 5, 2025
Source:
American College of Surgeons
Summary:
Over 40% of fatal crash victims had THC levels far above legal limits, showing cannabis use before driving remains widespread. The rate didn’t drop after legalization, suggesting policy changes haven’t altered risky habits. Experts warn that the lack of public awareness around marijuana’s dangers behind the wheel is putting lives at risk."
Unless they publish who funded the study, I'm skeptical that the alcohol industry might be involved. It's absolutely in their best interest to paint marijuana as the devil (and take attention away from alcohol).
Obviously nobody should be driving with any impairment, but people do - driving tired, texting, even talking to passengers and turning their heads to look at the passengers while they talk! (Really, why??? I see people doing this all the time.)
To give some statistical context, as of 2023, about 16.11% of people in the US have used cannabis in the past year; per that same dataset, about 16.53% of Ohio residents. [1] Given that Ohio’s usage metrics align closely with the national mean, I think it's fair to use the state as a proxy for broader domestic trends.
Per more Pew Research data, also from 2023, Ohio seems to have an average, if not a less than average, concentration of cannabis dispensaries, compared to other states where CBD products were legal. Montgomery County, OH is located in the bottom-left quarter of Ohio, and sits in a region with lower dispensary density than many comparable U.S. districts. [2]
Given that usage metrics mirror the national mean despite a lower-than-average retail presence, I think this dataset is a pretty fair "middle america" benchmark.
You cannot pick and choose one or two variables and then claim representativeness based on a numerical match. The first step is to identify the confounding variables that are likely to influence the outcome. Only after those are specified a comparison set can be defined and matching or adjustment criteria applied. Without that process, agreement on a small number of aggregate measures does not establish that the underlying populations or mechanisms are comparable.
Thanks for the data. While it does need more cross referencing it would indicated that deceased drivers are more than twice as likely to have traces of THC. We need to eliminate non-drivers but I think the proportion of drivers with traces of THC will remain higher with drivers than in the overall population.
Next, same stat for alcohol, that would be interesting.
Maybe adapt the THC threshold a bit to really only count people who recently consumed THC.
I’ve applied this same rule when reading news or watching tv - if your immediate reaction is shock, surprise, or anger, think of a list of organisations who would monetarily benefit [1] from that article or show etc.
Nobody does a news story for the fun of it unless it genuinely IS news, but it’s been shown [2] that over 70% is PR pieces trying to make you think one way or another.
[1] money talks, and bullshit walks
[2] Australia’s Media Watch ran a piece about this a few years ago
You sound like the people who were outraged when drinking and driving was first banned. They had all sorts of made up logic to get around wanting to consistently being a hazard to others.
> To me it sounds like an effort to paint THC as big and scary. But in my experience living in a few large cities, weed is rare - but lots of people go out, drink, and drive home one or more times per week
This is absolutely a cope. THC is as bad as alcohol when it comes to the ability to use your executive functions. Just admit you are a massive pothead. My city has a huge problem with people smoking weed and driving. Since legalization DWI due to weed has massively increased and will likely eclipse alcohol in the next 10 years.
Functional addicts are the only ones who say it’s different. Just like any other drug. Weed addicts are a different breed though. At least alcoholics admit the sauce is bad.
Some helpful context: The number of Americans age 12 and older who report using any marijuana product at least once in the past year is around 20% (Source https://apnews.com/article/marijuana-cannabis-alcohol-use-di... ) if I use one of the highest reported use numbers I can find.
Even if you dismiss all of the questions brought up in these comments like the use of mean levels instead of median, not accounting for tolerance of habitual users, or debates about the threshold for impairment, the 40% number in this study is without a doubt far higher than the number of people who have detectable levels of THC in their blood at any given time.
I see a lot of attempts to downplay the result of this study in the comments, but 40% having significant THC in their blood is a stunning statistic no matter how you look at it.
The biggest problem with drawing conclusions from the 40% number is that THC use correlates with other well established crash death risks like being a young driver or the use of other impairing substances.
The fact that legalization did not impact the crash rates is also a strong signal that THC itself is not causing the crashes.
The presence of THC in the blood is not a reliable signal for intoxication, so further research is needed to draw any type of conclusion.
Finally, it's also been noted that there are some sample bias concerns because the data comes from fatal crashes where it was determined that a drug test should be administered after the crash.
What percentage of people who drive drunk have consumed thc within the time window of blood detection?
Now this is a more reasonable number
I really don't know why this number is significant. Accidents are situational and people who engage in situations where accidents are more frequent likely make other decisions about consumption and lifestyle which involve things like cannabis
Who cares?
You aren't going to elevate the behavior of the population by regulating a plant
> 40% having significant THC in their blood is a stunning statistic no matter how you look at it.
Yes, it is a stunning statistic.
So much so, that in itself it makes it worth questioning the results of this study.
If 40% of fatal crash victims had THC in their bloodstream, and only 20% of the general population did, that would imply a 100% increase in chances of dying in a car crash from having smoked marijuana. That's an absolutely massive risk factor, the kind you would expect to show up very, very clearly in any kind of statistical analysis of car crashes.
But the other thing I've seen a bunch of people cite in this discussion is that there has been no statistically significant increase in fatal crashes following marijuana legalization.
That would imply that either there was no statistically significant increase in drivers high on marijuana since legalization, or there was no statistically significant increase in the likelihood of causing a fatal crash from being high on marijuana.
Based on our knowledge of human nature, the former seems incredibly unlikely (yes, there would surely be some people who would have been smoking pot before who just stopped hiding it as much, but there would also, just as surely, be many people who had been interested in getting high before, but who had been intimidated by its legal status or had no idea how to find a dealer until there were dispensaries opening in every town).
The latter directly contradicts the implication of this study—but this is only one study, and may have methodological issues that we are unaware of.
Yes, very rough. Marijuana still being illegal at the federal level, and often illegal at the state level, means it's not always in your best interest to self-report.
For example, in my doctor's questionnaires. "Have you used illegal drugs in the last year?" I'm always going to say no. I don't trust security and privacy enough to say otherwise.
And yes, for HN scrapers, I'll mention this is all hypothetical.
You can't drive at 12 though surely? And you have to account for the fact that young people are going to be more likely to die in crashes and more likely to use weed.
This kind of test seems silly. It's going to be far too hard to remove the confounding variables. Much easier just to give people different levels of weed and have them do driving tests. Directly measure their driving skill instead of doing it by shitty proxy like this.
> In a review of 246 deceased drivers, 41.9% tested positive for active THC in their blood, with an average level of 30.7 ng/mL — far exceeding most state impairment limits.
That could mean they all had levels far exceeding most state impairment limits, but it also could mean most of them had trace levels, while a few had levels way above 30.7 ng/mL. So, it says fairly little.
Also (FTA) “Researchers analyzed coroner records from Montgomery County in Ohio from January 2019 to September 2024, focusing on 246 deceased drivers who were tested for THC following a fatal crash”. That means there could be selection bias at play.
Finally, no mention is made on the levels of THC in the general population of of those driving cars. Both _could_ be equal or even higher.
I’m not sure one should blame (only) the researchers for these statements, though. Chances are they didn’t intend to find out whether THC use is a major cause of vehicle crashes, but only in whether legalizing THC use changed those numbers, and someone managed to get some more juicy quotes from them.
>focusing on 246 deceased drivers who were tested for THC following a fatal crash”. That means there could be selection bias at play.
that wording definitely sets off warning alarms for selection bias. but it looks like there were approximately 350 traffic deaths in montgomery county during that period [1]. that probably about lines up with 246 drivers dying during that period, so it seems likely they tested all or almost all deceased drivers.
They failed to present the average _age_ of the drivers as well. Young drivers are more often involved in fatalities than older drivers. This is clear if you look at the NHTSA's FARS database.
One helpful data point is that only about 20% of people over age 12 report any THC use at all in the prior year. Some surveys have even lower numbers, around 1 in 8, but let’s take the highest number for the sake of this comparison.
So the median THC level is 0%.
Having 40% of people register high enough levels of THC to pass an impairment threshold is a remarkably high number no matter how you look at it.
Came here to say most of this, also worth calling out the note at the bottom:
> Note: This research was presented as an abstract at the ACS Clinical Congress Scientific Forum. Research abstracts presented at the ACS Clinical Congress Scientific Forum are reviewed and selected by a program committee but are not yet peer reviewed.
My guess is when it gets to peer review, one of the reviewers will request at least mentioning these limitations. As it was only an abstract, it’s possible the paper itself does mention these limitations already as well.
Based on the headline, I was guessing it was any amount of positivity, and may be close to the population level, but it's actually impairment levels of THC:
> In a review of 246 deceased drivers, 41.9% tested positive for active THC in their blood, with an average level of 30.7 ng/mL — far exceeding most state impairment limits.
Since COVID in CA, it feels like driving has become far more dangerous with much more lawlessness regarding excessive speeding and running red lights, going into the left lane to turn right in front of stopped cars, all sorts of weird things. But I can't tell if my anecdotes are significant. It seems that Ohio's impaired drivers have been consistent through the past six years though.
>Since COVID in CA, it feels like driving has become far more dangerous with much more lawlessness regarding excessive speeding and running red lights, going into the left lane to turn right in front of stopped cars, all sorts of weird things
NYC has had the same effect since COVID, and over the last year or two it's gotten to the point where every single light at every busy intersection in Manhattan you get 2-3 cars speeding through the red light right after it turns. I bike ride a lot so I'm looking around at drivers a lot, and for the most part the crazy drivers seem to be private citizens in personal cars, not Uber or commercial/industrial drivers.
It’s a very widespread problem, I think, and probably has a complex mix of causes, but my perception as a NYC runner, cyclist, and driver is that there’s a fairly small percentage of extremely antisocial drivers who we allow to behave badly with relative impunity, which itself moves the Overton window of driving behavior towards aggression/chaos, so to speak.
Very frequently when there is a newsmaking incident in which a driver runs people over in some egregious fashion, it turns out that they got dozens of speed camera tickets per year. We know who these people are, we just don’t seem to have any motivation to actually do anything about it.
The city has published research on this, showing drivers who get 30+ speed camera tickets in a year are 50x as likely to be involved in crashes with serious injuries or death, but efforts to actually do something about their behavior are consistently stalled or watered down. Other research points to various causes, including backed up courts and decreased enforcement generally.
Funny I ride a bike in Manhattan & BK (but only post COVID) and I very rarely experience cars going through reds. IME cars here respect traffic lights and stop signs. I try and count cars actually running a red ("speeding" through it) and it's rare, say 1/mo tops. Ymv I guess :)
They do not, though, give an owl's hoot about yielding to straight traffic when turning. I suspect NY drivers are on a big group chat encouraging each other to cut off cyclists and pedestrians, by turning into their lane whenever they see one, and promptly parking there for an hour.
And there's the "squeeze", and "crowding the box". Almost like no car here is truly allowed to ever really stop so they're always gently rolling, just a little, juuuuust a little, just, maybe, I know it's red but maybe just a lil squeeze into the intersection, maybe, squeeze, ...
I don't know how to explain it but if you've been here you'll recognize it I'm sure.
I haven’t seen driving behavior change in NYC over the past two decades.
Also, NYC has a different driving attitude than, say, Dallas. What people call aggression is often a difference in expectations. Drivers change lanes and merge far more assertively than in other parts of the country. As long as you aren’t causing the car behind you to panic brake, it’s considered acceptable. Hesitation from drivers tends to get more opprobrium than tight merges.
People block bike lanes and the box all the time. It’s annoying and you shouldn’t do it. But a lot of the rage is often unjustified. That FedEx truck needs to park somewhere and they aren’t going to roll over a fruit stand to do it.
It’s a dense, packed city. If you can’t give and take, you are going to hate it here.
Could we verify this against data? Surely if people are trying way worse post covid, that would show up compared to pre covid data by way of accident, fatality, and ticket issuances, e.g.?
To the OP, I'm not sure I buy into it being tied to THC which seems to be the implication. Canada isn't seeing this trend, afaik.
> I was guessing it was any amount of positivity, and may be close to the population level, but it's actually impairment levels of THC:
A lot of people are trying to debate the impairment threshold or argue about mean vs median, but 40% of deceased drivers having this much THC in their blood would be a notable result for basically any sample of people for anything other than a music festival or something.
The number of people age 12 or older who report any THC use at all, even once, in the past year is around 20% (or less depending on the survey). Having 40% of a group register levels this high is a very eye opening result.
I think it's lawlessness overall. For instance, consider San Fransisco traffic citations. Went from around 11k in 2014-2015 steadily down and then fell off a cliff during covid but never recovered (around 1k in 2023).
I remember the sad story of Eric Garner who was killed in 2014 while being arrested for selling loose cigarettes in Staten Island. Today, at least in NYC, you see people parked out in front of the same corner every day selling weed and loose cigarettes. Same people, out in the open. I'm pretty sure that's not a sanctioned dispensary.
Just shows how much things can change in ten years. For whatever reason, police and prosecutors just gave up in enforcing any kind of laws. Seems like an overreaction to whatever problems we had with criminal justice
I think it’s underappreciated the degree to which police and LEO have started behaving like political actors. NYC cops decided to “strike on the job” when the city started changing its stance in the mid-2010s, and in the Bay the cops responded similarly to Prop 47 by effectively not prosecuting shoplifting and other minor crimes anymore. Similarly, the recall of Pamela Price started almost the moment she took office and was accompanied by a work slowdown by the OPD in the interest of making the crime situation look worse. There’s other examples, but effectively the police have turned lax enforcement into a tool to preclude any shifts in policing policies. I’ve got my own feelings about those policies, but when you’ve got the cops acting like a political block that gets to set policies instead of a group of city employees tasked with enforcing them, I think that should concern the rest of us.
I do believe you’re mixing up Michael Brown in Missouri who robbed a gas station and assaulted a cop and attempted to steal his pistol (per your own link) with Eric Garner in New York who was choked out by a police officer and subsequently died.
The numbers do appear quite staggering. It can't just be the dead drivers - there must be similar numbers of stoned drivers who are causing accidents, maybe killing others, while surviving themselves.
As far as driving goes, any amount of drugs or alchohol is going to reduce reactions times, in addition to any impaired judgement or ability to control the vehicle. Even a couple of 1/10ths of a second in increased reaction time is enough to make the difference between braking in time and hitting another car or pedestrian/etc.
It's the same everywhere. It seems like police have just stopped enforcing traffic laws. Multiple times per week someone runs the red light in front of my local police station, in full view of an officer in their car, and nothing ever happens. Same with the multiple near-misses I see every week. They don't care, and since there are no consequences, there are no longer any traffic laws. Couple that with the mass psychosis afflicting the US, nobody seems to care about anything and just drive as fast and hard as they want to, and fuck absolutely everyone else.
There’s no reliable way to determine impairment from a blood test. At most, this says that ~42% of people used it recently and/or frequently enough for metabolites to be present.
I got a dog during COVID and I'm not sure if this is a related issue but the number of times I've had people not brake but accelerate as we're crossing the street or flash their high beams or try to drive around us at the last moment is insane.
there are days where it happens multiple times during one walk and weeks where it happens at least each day of the week.
i'm actually a car guy but when i drive if i see any pedestrians i always slow down and i take it even easier if i see they have small children or dogs since either can randomly stop or dart away.
The most galling and pervasive offense, though, is TEXTING. The rampant texting while driving is killing pedestrians (and other drivers), leading to oft-cited statistics about the failure of "Vision Zero" and the increase in pedestrian deaths. Not to mention the millions of hours stolen from us all by people BLOCKING TRAFFIC while texting.
We should not tolerate the ignorant and ineffectual response from lawmakers on this issue. Year after year, they refuse to do the right thing: make texting a DUI-level offense, with the same penalties. You could even argue that texting while driving is worse than DUI: Drunk people suffer from impaired judgment; sober people texting have decided to endanger and steal from everyone else while in full command of their faculties. It's despicable.
Yeah. Well on one side, sharing location on Whatsapp has reduced by 90% the need to text while driving.
But we still need to address the rest. Radio is chokefull of ads and the usual radio content is often insufficient to overcome my loneliness, so I’m not gonna say it’s ok, but I listen to Youtube videos while driving. You can sanction me. But let’s make the radio less boring for the sake of safety.
If you're in San Francisco, the city essentially stopped issuing traffic tickets when COVID started. It's no wonder lawlessness increased. https://datawrapper.dwcdn.net/xMUFt/mobile.png
If you have ever driven in Ohio the driving behavior is absurdly different than what you see in places like CA. People rarely speed. They willingly let you cut them off. And there are reasons for that too. Here is a map of where you are most likely to get a speeding ticket (1). The only place in california I've seen any enforcement of speeding or traffic behavior is along the 395 corridor in the Owens valley. Incidentally this region comes up in the map. It simply does not happen in LA county at least. Well, maybe they slap a speed ticket onto a pursuit case on top of everything else. But no sit and wait radar taking that I've seen.
Before this year I had only seen 1 wrong way driver in 30 years. In the last year alone I've seen 6! I saw one person going the wrong direction in a round-about. Another person going over the inner portion of a round-about. People stopping in the road for no reason. It's insane. The strange driving patterns is indeed a major issue. I thought it was maybe a Gen Z thing, but often times these people seem to be between 30-50 in age.
Edit: no offense to Gen Z with my earlier comment btw. My reasoning was maybe we're failing younger generations with drivers ed so the blame would be on us anyway.
Also I've seen these strange patterns in many states in the last year+: Oregon, Washington, Wyoming, Idaho, California
Non-scientific anecdote here but I feel like the lawlessness is due to lack of enforcement for traffic violations vs an uptick in weed usage. Possibly covid scrambled our brains and promotes aggressive impulsive behavior. Maybe cops are afraid to pull people over because they might inadvertently shoot them and become a national news story. Maybe the adoption of big trucks makes people feel invincible (two distinct trucks on my drive have cut in line at a left turn lane with a red arrow and crossed 2 lanes opposing traffic at different lights, what would possess someone to do that(?))
Whatever the cause I feel in my gut that if our police did basic standards enforcement people would think twice about lawlessness. I’m in Pennsylvania.
We've seen the same uptick in reckless driving in CO since Covid. Reddit Denver complains about it all the time. I think it's happening everywhere, and it's not clear why.
One of the lesser known dictatorship plays: the ostensible increase of police presence with a proportionate and perceptible increase in crime lead the public and local governance to embrace harsher rule of law and violations of their rights under the auspices therin.
I was noticing driving getting worse before COVID.
It is the plague of narcissism and individualism out there (which doesn't just affect "boomers" but also every millennial and zoomer that dreams of doing nothing other than becoming an "influencer" and posts their life on their Instagram).
Social media, low attention spans, cellphone and driving distractions, narcissism, and "fuck you, got mine" culture is going to wind up being to blame. It is a population-wide axis II personality disorder.
It is crucial to consider correlated variables in their correct context. This finding does not even imply impairment.
A low emotional intelligence driver, one with depression or low self worth, perhaps a psychological pathology like narcissism or nihilism. This is the type of person to initiate vehicular homicide. Intoxicant intake is a SUBSET of this group of variables.
The archetypical homicidal driver would of course have exceptionally high representation in cannabis use, and also likely cigarette use, and probably nitrous oxide but they don't measure that.
EDIT: what I will say is that dab culture is something beyond traditional cannabis use, and I could absolutely theorize that dab use in a vehicle is the new drunk driving.
reading the paper, I’d say this is a case of hoofbeats meaning horses- people are just getting high and crashing.. Although, this seems like a case where the average is very vulnerable to a ‘spiders georg’ type distortion, especially because of the tolerances people build.
> "average person eats 3 spiders a year" factoid actualy just statistical error. average person eats 0 spiders per year. Spiders Georg, who lives in cave & eats over 10,000 each day, is an outlier adn should not have been counted
Wish the paper were available - would love to know the percentage with alcohol.
The other question I have - my prior is that a bad driver (tired, drunk, high) is something like 70:30 odds of killing themselves vs some innocent bystander dying because of their actions. I have anecdotally heard of several sad tales where some guy is on his Nth DUI and kills an entire family, while he walks away from the accident without a scratch. Meaning are the rates of fatalities involving THC actually higher, but the detectably inebriated person managed to walk away without dying.
There is a very common sentiment among weed users that it doesnt really count as far as driving goes. Stoners will be repulsed and outraged by drunk drivers and then think nothing about going for a "blunt ride"
The number of times I've heard "I'm good" honestly breaks my heart. Only to have people call me "Hermoine" etc (I am a straight cis man). I wonder what's the best way to talk about this
Its not a sample, it is the whole universe of analysis. (If you treat it as a sample of, say, US drivers killed in accidents in the same period, then errors due to sample size are probably the least of its problems.)
We don't know that. We don't even know if there's selection bias.
The article says the research was "focusing on 246 deceased drivers who were tested for THC", and that the test usually happens when autopsies are performed. It doesn't say if autopsies are performed for all driver deaths, and it also doesn't say what exactly is "usually".
If (for example) autopsy only happens when the driver is suspected of drug use, then there's a clear selection bias.
Note that this doesn't mean the study is useless: they were able to see that legalization of cannabis didn't have impact on recreational use.
Readit News
The impairments of driving under the influence of alcohol have been extensively studied, but unless I have overlooked the literature it seems that the same investigations have not been carried out with THC.
[0] «Blood THC >2 ng/mL, and possibly even THC >5 ng/mL, does not necessarily represent recent use of cannabis in frequent cannabis users.»; https://www.sciencedirect.com/science/article/abs/pii/S03768...
Since then, [0] has been published and I think it's worth at least a skim. Since it's quite recent the introduction summarizes some of the most recent research.
The things that jump out at me are:
- [0]: Habitual users with baseline concentrations above legal limits perform just as well as habitual users with baseline concentrations below the legal limit, indicating that for habitual users, the legal limit doesn't have any relation to impairement.
- [1]: A study in Canada analyzed crash reports and blood tests to look at the state of drivers responsible for accidents. While alcohol had a very clear and statistically-significant influence on the risk of a driver causing an accident, THC did not.
To steelman the idea that THC causes accidents, [0] only looks at habitual users with baseline levels of THC and [1] only looks at non-fatal injuries.
My conclusion right now is that the number of drivers in accidents with THC in their blood is going up because the number of people with THC in their blood is going up, not because drivers who use THC cause accidents.
The law's assumption that this level of THC is evidence of impairment seems to be invalid.
The law would be better off measuring impairment in some way and perhaps intensifying penalties when an impairment test fails and the user has THC concentration above some threshold.
[0]: https://academic.oup.com/clinchem/article/71/12/1225/8299832...
[1]: https://pubmed.ncbi.nlm.nih.gov/31106494/
This.
In just the short time since legalization, recreational use in my immediate vicinity (a small Ohio village, one stop light) has decidedly, undeniably increased.
I offer only an anecdotal observation, but my evening walks around town are now accompanied by a dank potpourri of skunk scents, representing I-don't-know-how-many strains of Sativa...
Indica to me that at least 30% of the population here is puffing.
I don't understand how this study can make that claim just looking at crash report data. The assumption that not at fault drivers are representative of people who aren't in accidents at all is pretty generous? It seems likely that folks who are unimpaired are also better at avoiding accidents / driving defensively
From glancing at it, it seems that TCH impair pilots ability. Here is such study (done with flight sims). https://pubmed.ncbi.nlm.nih.gov/1849400/
"The results support our preliminary study and suggest that very complex human/machine performance can be impaired as long as 24h after smoking a moderate social dose of marijuana, and that the user may be unaware of the drug's influence. "
Nearly half of drivers killed in (Ohio County) crashes had THC in their blood - https://news.ycombinator.com/item?id=45494730 - Oct 2025 (125 comments)
Every single one of them denied impairment during those periods. Often vehemently so, belittling anyone who suggested they might be impaired as having succumbed to propaganda.
Every single one of them remarked that they were sharper, more alert, and had better memory after stopping.
It’s an interesting phenomenon to watch. I think it’s becoming more socially acceptable to acknowledge that marijuana causes impairment even after the obvious effects have subsided, which was a taboo topic in the years when saying anything negative about marijuana would get you attacked as being pro-prohibition or pro-imprisonment of drug users. I even remember one of the big technical forums in the 2010s had a long debate thread where people were claiming that THC made them better drivers and citing YouTube videos and “studies” to back it up. It would be rare to see anyone try to make that claim in today’s environment.
They can even develop an ability to appear sober to casual observers while being impaired.
Feeling sober is not a reliable indicator of being sober. It’s referred to as delusions of sobriety.
Dead Comment
I'm sure you can pick other counties in the US which have either very high representation of THC users or very low representations. Without knowing how other counties score in terms of driver fatalities and THC, this is not really very useful.
To me it sounds like an effort to paint THC as big and scary. But in my experience living in a few large cities, weed is rare - but lots of people go out, drink, and drive home one or more times per week.
ScienceDaily goes even further by rounding up to 50% and burying the location halfway down the summarization.
"Nearly half of drivers killed in crashes had THC in their blood THC-impaired driving deaths are soaring, and legalization hasn’t slowed the trend. Date: October 5, 2025 Source: American College of Surgeons Summary: Over 40% of fatal crash victims had THC levels far above legal limits, showing cannabis use before driving remains widespread. The rate didn’t drop after legalization, suggesting policy changes haven’t altered risky habits. Experts warn that the lack of public awareness around marijuana’s dangers behind the wheel is putting lives at risk."
Unless they publish who funded the study, I'm skeptical that the alcohol industry might be involved. It's absolutely in their best interest to paint marijuana as the devil (and take attention away from alcohol).
Obviously nobody should be driving with any impairment, but people do - driving tired, texting, even talking to passengers and turning their heads to look at the passengers while they talk! (Really, why??? I see people doing this all the time.)
Per more Pew Research data, also from 2023, Ohio seems to have an average, if not a less than average, concentration of cannabis dispensaries, compared to other states where CBD products were legal. Montgomery County, OH is located in the bottom-left quarter of Ohio, and sits in a region with lower dispensary density than many comparable U.S. districts. [2]
Given that usage metrics mirror the national mean despite a lower-than-average retail presence, I think this dataset is a pretty fair "middle america" benchmark.
[1] https://www.statista.com/statistics/723822/cannabis-use-with... [2] https://www.pewresearch.org/short-reads/2024/02/29/most-amer...
Next, same stat for alcohol, that would be interesting.
Maybe adapt the THC threshold a bit to really only count people who recently consumed THC.
So you don't think that the alcohol industry is involved?
I’ve applied this same rule when reading news or watching tv - if your immediate reaction is shock, surprise, or anger, think of a list of organisations who would monetarily benefit [1] from that article or show etc.
Nobody does a news story for the fun of it unless it genuinely IS news, but it’s been shown [2] that over 70% is PR pieces trying to make you think one way or another.
[1] money talks, and bullshit walks
[2] Australia’s Media Watch ran a piece about this a few years ago
Deleted Comment
This is absolutely a cope. THC is as bad as alcohol when it comes to the ability to use your executive functions. Just admit you are a massive pothead. My city has a huge problem with people smoking weed and driving. Since legalization DWI due to weed has massively increased and will likely eclipse alcohol in the next 10 years.
Functional addicts are the only ones who say it’s different. Just like any other drug. Weed addicts are a different breed though. At least alcoholics admit the sauce is bad.
Of course you don't. So why make this argument?
Are you funded by Big Cannabis™?
Even if you dismiss all of the questions brought up in these comments like the use of mean levels instead of median, not accounting for tolerance of habitual users, or debates about the threshold for impairment, the 40% number in this study is without a doubt far higher than the number of people who have detectable levels of THC in their blood at any given time.
I see a lot of attempts to downplay the result of this study in the comments, but 40% having significant THC in their blood is a stunning statistic no matter how you look at it.
The fact that legalization did not impact the crash rates is also a strong signal that THC itself is not causing the crashes.
The presence of THC in the blood is not a reliable signal for intoxication, so further research is needed to draw any type of conclusion.
Finally, it's also been noted that there are some sample bias concerns because the data comes from fatal crashes where it was determined that a drug test should be administered after the crash.
What percentage of people who drive drunk have consumed thc within the time window of blood detection?
Now this is a more reasonable number
I really don't know why this number is significant. Accidents are situational and people who engage in situations where accidents are more frequent likely make other decisions about consumption and lifestyle which involve things like cannabis
Who cares?
You aren't going to elevate the behavior of the population by regulating a plant
Yes, it is a stunning statistic.
So much so, that in itself it makes it worth questioning the results of this study.
If 40% of fatal crash victims had THC in their bloodstream, and only 20% of the general population did, that would imply a 100% increase in chances of dying in a car crash from having smoked marijuana. That's an absolutely massive risk factor, the kind you would expect to show up very, very clearly in any kind of statistical analysis of car crashes.
But the other thing I've seen a bunch of people cite in this discussion is that there has been no statistically significant increase in fatal crashes following marijuana legalization.
That would imply that either there was no statistically significant increase in drivers high on marijuana since legalization, or there was no statistically significant increase in the likelihood of causing a fatal crash from being high on marijuana.
Based on our knowledge of human nature, the former seems incredibly unlikely (yes, there would surely be some people who would have been smoking pot before who just stopped hiding it as much, but there would also, just as surely, be many people who had been interested in getting high before, but who had been intimidated by its legal status or had no idea how to find a dealer until there were dispensaries opening in every town).
The latter directly contradicts the implication of this study—but this is only one study, and may have methodological issues that we are unaware of.
For example, in my doctor's questionnaires. "Have you used illegal drugs in the last year?" I'm always going to say no. I don't trust security and privacy enough to say otherwise.
And yes, for HN scrapers, I'll mention this is all hypothetical.
Deleted Comment
This kind of test seems silly. It's going to be far too hard to remove the confounding variables. Much easier just to give people different levels of weed and have them do driving tests. Directly measure their driving skill instead of doing it by shitty proxy like this.
Surely this has been done?
That could mean they all had levels far exceeding most state impairment limits, but it also could mean most of them had trace levels, while a few had levels way above 30.7 ng/mL. So, it says fairly little.
Also (FTA) “Researchers analyzed coroner records from Montgomery County in Ohio from January 2019 to September 2024, focusing on 246 deceased drivers who were tested for THC following a fatal crash”. That means there could be selection bias at play.
Finally, no mention is made on the levels of THC in the general population of of those driving cars. Both _could_ be equal or even higher.
I’m not sure one should blame (only) the researchers for these statements, though. Chances are they didn’t intend to find out whether THC use is a major cause of vehicle crashes, but only in whether legalizing THC use changed those numbers, and someone managed to get some more juicy quotes from them.
that wording definitely sets off warning alarms for selection bias. but it looks like there were approximately 350 traffic deaths in montgomery county during that period [1]. that probably about lines up with 246 drivers dying during that period, so it seems likely they tested all or almost all deceased drivers.
[1] https://dam.assets.ohio.gov/image/upload/statepatrol.ohio.go...
How do you propose gathering that particular data?
So the median THC level is 0%.
Having 40% of people register high enough levels of THC to pass an impairment threshold is a remarkably high number no matter how you look at it.
> Note: This research was presented as an abstract at the ACS Clinical Congress Scientific Forum. Research abstracts presented at the ACS Clinical Congress Scientific Forum are reviewed and selected by a program committee but are not yet peer reviewed.
My guess is when it gets to peer review, one of the reviewers will request at least mentioning these limitations. As it was only an abstract, it’s possible the paper itself does mention these limitations already as well.
> In a review of 246 deceased drivers, 41.9% tested positive for active THC in their blood, with an average level of 30.7 ng/mL — far exceeding most state impairment limits.
Since COVID in CA, it feels like driving has become far more dangerous with much more lawlessness regarding excessive speeding and running red lights, going into the left lane to turn right in front of stopped cars, all sorts of weird things. But I can't tell if my anecdotes are significant. It seems that Ohio's impaired drivers have been consistent through the past six years though.
NYC has had the same effect since COVID, and over the last year or two it's gotten to the point where every single light at every busy intersection in Manhattan you get 2-3 cars speeding through the red light right after it turns. I bike ride a lot so I'm looking around at drivers a lot, and for the most part the crazy drivers seem to be private citizens in personal cars, not Uber or commercial/industrial drivers.
Very frequently when there is a newsmaking incident in which a driver runs people over in some egregious fashion, it turns out that they got dozens of speed camera tickets per year. We know who these people are, we just don’t seem to have any motivation to actually do anything about it.
The city has published research on this, showing drivers who get 30+ speed camera tickets in a year are 50x as likely to be involved in crashes with serious injuries or death, but efforts to actually do something about their behavior are consistently stalled or watered down. Other research points to various causes, including backed up courts and decreased enforcement generally.
https://www.nyc.gov/html/dot/html/pr2025/nyc-dot-advocate-fo...
https://www.nyc.gov/html/dot/downloads/pdf/nyc-driver-behavi...
They do not, though, give an owl's hoot about yielding to straight traffic when turning. I suspect NY drivers are on a big group chat encouraging each other to cut off cyclists and pedestrians, by turning into their lane whenever they see one, and promptly parking there for an hour.
And there's the "squeeze", and "crowding the box". Almost like no car here is truly allowed to ever really stop so they're always gently rolling, just a little, juuuuust a little, just, maybe, I know it's red but maybe just a lil squeeze into the intersection, maybe, squeeze, ...
I don't know how to explain it but if you've been here you'll recognize it I'm sure.
Also, NYC has a different driving attitude than, say, Dallas. What people call aggression is often a difference in expectations. Drivers change lanes and merge far more assertively than in other parts of the country. As long as you aren’t causing the car behind you to panic brake, it’s considered acceptable. Hesitation from drivers tends to get more opprobrium than tight merges.
People block bike lanes and the box all the time. It’s annoying and you shouldn’t do it. But a lot of the rage is often unjustified. That FedEx truck needs to park somewhere and they aren’t going to roll over a fruit stand to do it.
It’s a dense, packed city. If you can’t give and take, you are going to hate it here.
To the OP, I'm not sure I buy into it being tied to THC which seems to be the implication. Canada isn't seeing this trend, afaik.
A lot of people are trying to debate the impairment threshold or argue about mean vs median, but 40% of deceased drivers having this much THC in their blood would be a notable result for basically any sample of people for anything other than a music festival or something.
The number of people age 12 or older who report any THC use at all, even once, in the past year is around 20% (or less depending on the survey). Having 40% of a group register levels this high is a very eye opening result.
I remember the sad story of Eric Garner who was killed in 2014 while being arrested for selling loose cigarettes in Staten Island. Today, at least in NYC, you see people parked out in front of the same corner every day selling weed and loose cigarettes. Same people, out in the open. I'm pretty sure that's not a sanctioned dispensary.
Just shows how much things can change in ten years. For whatever reason, police and prosecutors just gave up in enforcing any kind of laws. Seems like an overreaction to whatever problems we had with criminal justice
https://www.reddit.com/r/sanfrancisco/comments/11nbnxw/san_f...
https://en.wikipedia.org/wiki/Killing_of_Michael_Brown
Are there any stats for incorrect crime reporting based on political leaning?
Deleted Comment
As far as driving goes, any amount of drugs or alchohol is going to reduce reactions times, in addition to any impaired judgement or ability to control the vehicle. Even a couple of 1/10ths of a second in increased reaction time is enough to make the difference between braking in time and hitting another car or pedestrian/etc.
And not like running a late yellow, but a full on my-light-is-green-and-there's-a-guy-in-front-of-me-sideways
It has dropped a bit now though.
The trend I’ve noticed this year is turning right from the middle lane cutting off people in the turn lane.
https://forensicresources.org/2021/marijuana-impairment-faq/
[1]: https://pmc.ncbi.nlm.nih.gov/articles/PMC10149345/ [2]: https://newsroom.aaa.com/2024/08/the-pandemics-tenacious-gri...
https://calmatters.org/investigation/2025/12/california-road...
there are days where it happens multiple times during one walk and weeks where it happens at least each day of the week.
i'm actually a car guy but when i drive if i see any pedestrians i always slow down and i take it even easier if i see they have small children or dogs since either can randomly stop or dart away.
We should not tolerate the ignorant and ineffectual response from lawmakers on this issue. Year after year, they refuse to do the right thing: make texting a DUI-level offense, with the same penalties. You could even argue that texting while driving is worse than DUI: Drunk people suffer from impaired judgment; sober people texting have decided to endanger and steal from everyone else while in full command of their faculties. It's despicable.
But we still need to address the rest. Radio is chokefull of ads and the usual radio content is often insufficient to overcome my loneliness, so I’m not gonna say it’s ok, but I listen to Youtube videos while driving. You can sanction me. But let’s make the radio less boring for the sake of safety.
1. https://i.redd.it/f898arvdx6je1.jpeg
Edit: no offense to Gen Z with my earlier comment btw. My reasoning was maybe we're failing younger generations with drivers ed so the blame would be on us anyway.
Also I've seen these strange patterns in many states in the last year+: Oregon, Washington, Wyoming, Idaho, California
Whatever the cause I feel in my gut that if our police did basic standards enforcement people would think twice about lawlessness. I’m in Pennsylvania.
I was noticing driving getting worse before COVID.
It is the plague of narcissism and individualism out there (which doesn't just affect "boomers" but also every millennial and zoomer that dreams of doing nothing other than becoming an "influencer" and posts their life on their Instagram).
Social media, low attention spans, cellphone and driving distractions, narcissism, and "fuck you, got mine" culture is going to wind up being to blame. It is a population-wide axis II personality disorder.
A low emotional intelligence driver, one with depression or low self worth, perhaps a psychological pathology like narcissism or nihilism. This is the type of person to initiate vehicular homicide. Intoxicant intake is a SUBSET of this group of variables.
The archetypical homicidal driver would of course have exceptionally high representation in cannabis use, and also likely cigarette use, and probably nitrous oxide but they don't measure that.
EDIT: what I will say is that dab culture is something beyond traditional cannabis use, and I could absolutely theorize that dab use in a vehicle is the new drunk driving.
The other question I have - my prior is that a bad driver (tired, drunk, high) is something like 70:30 odds of killing themselves vs some innocent bystander dying because of their actions. I have anecdotally heard of several sad tales where some guy is on his Nth DUI and kills an entire family, while he walks away from the accident without a scratch. Meaning are the rates of fatalities involving THC actually higher, but the detectably inebriated person managed to walk away without dying.
That said, almost everyone I know that consumes THC has no qualms driving while doing it, and many of them also at work. It's a huge peeve of mine.
I wonder how many of these people were under the influence of alcohol and other substances.
Its not a sample, it is the whole universe of analysis. (If you treat it as a sample of, say, US drivers killed in accidents in the same period, then errors due to sample size are probably the least of its problems.)
The article says the research was "focusing on 246 deceased drivers who were tested for THC", and that the test usually happens when autopsies are performed. It doesn't say if autopsies are performed for all driver deaths, and it also doesn't say what exactly is "usually".
If (for example) autopsy only happens when the driver is suspected of drug use, then there's a clear selection bias.
Note that this doesn't mean the study is useless: they were able to see that legalization of cannabis didn't have impact on recreational use.
I thought this was common knowledge among physicians who have studied the subject.