How Drunk Is Too Drunk to Drive?

Our podcast “The Suicide Paradox” featured sociologist David Phillips, who spoke about his research on copycat suicides (a phenomenon he calls “the Werther Effect”). More recently, Philips has been studying drunk driving. Particularly, he’s been looking at drivers who are merely “buzzed” — with 0.01 percent blood alcohol concentrations (BACs) — and has found that the severity of life-threatening motor vehicle accidents increases significantly at BACs far lower than the current U.S. limit of 0.08 percent. In an email, Philips describes his latest research on buzzed drivers:

My current research, just published in Injury Prevention, shows that even minimally buzzed drivers (with BAC=0.01%) are 46% more likely to be blamed for an accident than are the sober drivers they collide with. This indicates that there is no safe level of alcohol for drivers: any amount of alcohol markedly increases the risk to drivers and their passengers. We reached this conclusion after examining an official, U.S. dataset of more than 570,000 car crashes. The findings have implications for drivers, passengers, police, judges, lawyers, insurance companies, advocacy organizations (like MADD) and regulatory agencies.

The paper, “Official blame for drivers with very low blood alcohol content: there is no safe combination of drinking and driving” (abstract; PDF), is co-authored with Ana Luiza Sousa and Rebecca Moshfegh. The researchers used an official nationwide U.S. database (Fatality Analysis Reporting System) for the years 1994–2011. They found that there’s “no sudden transition from blameless to blamed drivers at BAC=0.08% (the U.S. legal limit). Instead, sole official blame increases smoothly and strongly with BAC (r=0.98 (0.96–0.99) for male drivers, p<0.000001; r=0.99 (0.97–0.99) for female drivers, p<0.000001). This near-linear SOB-to-BAC relationship begins at BAC=0.01% and ends around BAC=0.24%.”


"Official blame" is not the same thing as actual responsibility for a crash.


The causal link between drinking and recieving "offical blame" may not be impairment. It could well be a bias held by reporting officers against people who admit to drinking before getting behind the wheel - a bias which is shown in the presumptive title of the study itself!


It's a good point that impairment increases continuously as BAC increases, but it doesn't follow that we should punish those at .01% BAC. Many other physical/psychological states impair driving (tiredness from lack of sleep, fatigue from a long day at work, stress or anger from a fight with a spouse, distraction from a conversation with a passenger) yet we make no attempt to quantify the impairment of such states. We probably should quantify the impairment if only for the sake of comparison.

I suspect that (a) blame tends to go to a driver with non-zero BAC by default, and (b) the increase in risk from being at low BAC levels (as opposed to zero) is smaller than the factors mentioned above, which we ignore. If we are going to pass new driving laws, we should be targeting the biggest risk factors. I doubt low BAC drivers are very high on the list considering many states still have weak or absent cell phone driving laws.



Legalize marijuana and we wouldn't have as much of this problem.


This sounds like a classic case of reverse causality. The police only breathalyze people who they think are at fault...

Phil Persinger

It's both amusing and illuminating to be in an Australian city when the bars close and to see all the revelers and bar-flies pour themselves into taxis for the ride home. Cars are retrieved the next day after coffee.

The max legal BAC in Oz is .05% and drivers are admonished that impairment begins at lower levels

.. and this in the land of Foster's, XXXX beer and Bundaberg rum.


My guess is that this research will increase the % of buzzed drivers that are blamed for a crash.

James Halliday

I've always been interested in the effects of ageing on the ability to drive.
Some countries seem to be slowly pushing for mandatory re-tests/examination, but until that point there seems to be an assumption that you're absolutely fine.
Alcohol is always (and rightly) something that's focussed on as a deliberate, self-inflicted, impairment to your ability to drive safely - but there are so many other factors that are completely ignored.
Another one might be eye-sight. Surely it makes sense that if you're driving you've done your best to optimize/correct your vision - but I'm unaware of any attempt to enforce mandatory eye-testing and wearing of resultant corrective devices, before you're designated a 'safe driver'.
Would be interesting to get access to insurance companies raw data. Theoretically, you start as a teenager as a 'high risk' and your premiums (adjusting for speeding tickets, DUI convictions, car cost, estimated mileage etc) should decrease. If we could track where this didn't happen, it would be fascinating to know why.


Enter your name...

Having slightly imperfect vision might not increase accidents, so true optimization is probably not necessary. Also, it's more complicated than that: what if laser vision correction makes mine better than yours during the day, but a little worse than yours at night? Do we ban you from driving during the day because yours isn't "optimized"?

Every single time I've gotten a driver's license, I've had to take a vision test. I don't know about other countries, but in the US, eye-testing and wearing any necessary corrective lenses is required. It's marked on the driver's license, so it's easy to enforce.


I'll keep piling on. How does an officer find someone with .01% BAC? By suspecting the person of being drunk. Someone who appears drunk at even .01% BAC is probably more likely to be a bad driver in general. Drivers who don't appear drunk at .01% BAC aren't going to get tested at all. So the .01% crowd here isn't going to be representative of all drivers with .01% BAC.

I suspect that all this study has shown is that bad drivers sometimes also have a non-zero BAC.


Good point. Also, were they tested for anything else? You might have .01% BAC and a much higher percent of some other drug.


I'm wondering if the authors of the study controlled for other factors, like cell phone use, lack of sleep, time of day, objects/animals in the road, etc. Should we start charging drivers for lack of proper rest behind the wheel? We do that for commercial truck drivers - why not people driving on personal business? How about distracted driving by having a bunch of screaming kids or loud music, or the myriad of other factors the make driving a somewhat risky pursuit?

caleb b

As the Freakonomics authors themselves are well aware, drunk driving is a sensitive subject with only one moral side. The post about drunk walking came with disclaimer after disclaimer explaining that they were not advocated that folks drink and drive....just that walking can also be dangerous (in fact more so - so call a cab). Regardless, simply talking about the dangers of drunk walking was enough to generate mounds of hate mail, vows to never return to the site, wailing and gnashing of teeth, etc.

The moral absoluteness of being against drunk driving can never be questioned.

That said, while this study focuses on BAC levels of those involved in crashes, what it fails to mention is the BAC levels of those NOT involved in crashes, which is many multiples more. Perhaps this entire study is subject to selection bias as predominately bad drivers get into accidents and drinking alcohol harms their ability to drive at a somewhat linear pace. Since the study doesn’t include all drivers who drink, it can’t really provide definitive evidence as to a level of BAC that is “safe.”

Alcohol sales in restaurants, bars, night clubs, movie theaters, heck even museums suggest that millions of people drink and drive every single day. This Sunday, tens of millions of people will be watching the Super Bowl and likely millions of people will be driving with alcohol in their system. Yet, only a tiny fraction of these individuals will be involved in accidents. Of those, very few will result in fatalities. The sheer numbers involve indicated that safe driving while consuming alcohol is being achieved by millions, suggesting the .08 limit is probably about right.


caleb b

On a personal note...

According to my Brookstone $25 at-home breathalizer, I don't even start to get buzzed until around .08, and i'm not good and drunk until .12,and "not able" to drive home at .16, so in my case "buzzed driving" does litterally mean drunk driving.

In case you are curious, .20 is "smashed" and the device doesn't register beyond this level to discourage people from testing their limits. I'm glad too, because i pretty much pass out after .20 anyway.

steve cebalt

I wonder who funded the research and whether it was done for a purpose? For an advocacy group (MADD), an insurance company, etc? It strikes me as research done with an agenda -- not that such an agenda would discredit it, but it would be good to know. I couldn't tell one way or another from the link.

I ask because as a PR professional, the heavy-handed title of the paper makes me blush:

“Official blame for drivers with very low blood alcohol content: there is no safe combination of drinking and driving.”

Shifting gears, if society really cared about drunk driving, it would prosecute it for what it is when it results in violence -- assault with a deadly weapon or murder, depending on whether the victim lives or dies. No need to police the traffic or measure blood levels of harmless drivers t0 two decimal points. Just consistently prosecute drunk people who actually hurt other people (or property) to the full limits of the law, and far fewer people would bear the risk of driving with ANY alcohol in their system, since you can never really tell when you're drunk. Cheap, effective prosecution. If people wanna drive drunk, fine, they're free to do so; if anyone gets hurt (people or property), they do hard time or life in prison.

I know how complex this issue is. When a person is drinking, common sense and good judgment are forfeited at a point unknown to the drinker. One drink? Two? Three? There are too many variables, and they vary each time one drinks. It is simply unknowable. So no preaching from me. Hence my focus on the actual consequences that we wish to deter: Violence to innocent people and their property.



I'll add to what others have said: unless you test ALL drivers involved in a set of accidents, there's no way to determine whether alcohol is at fault. As for instance there's an accident, Joe is presumed at fault, is tested, and found to have a BAC of 0.01. Susie, the other driver, isn't tested, even though she actually has a BAC of 0.05.