Is blood alcohol level alone a fair measure of impairment?

This is both a request for factual information and an opinion about how it might be applied.

The Washington Post ran a story Sunday about the consequences of a drunken driving arrest. They followed the cases of everybody arrested for dwi/dui in one suburban county in one week, almost 100 people. A blood alcohol level of .08 or more is considered proof of drunken driving, and almost everyone was convicted on that basis. Most first offenders got probation and mandatory counseling, they lost their licenses for a year and had to pay fines, court costs and attorney fees. The paper calculated that the direct cost of the arrest totals between $5,000 and $20,000 for each driver. In addition, some people lost their jobs, some went to jail because they couldn’t pay fines, and in one case a marriage broke up. One woman who had one drink at dinner with friends landed in jail.

This paragraph startled me:

In effect, an action that would not be illegal for some people becomes a serious crime for others based on gender and ethnicity.

This leads me to ask whether blood alcohol level, by itself, is a valid measure of impairment. Suppose you lined up 100 people from every background, a rainbow of the human race, and administered enough alcohol to raise every person’s blood alcohol level to exactly .08. Using standard computerized tests for coordination, reaction time, depth perception etc., would all 100 people be impaired to the same degree? If so, then using the blood alcohol measure to lock people up is probably fair. But if there are differences in performance when blood alcohol level is the same, then applying that rigid standard across the board seems inherently unfair, especially when the legal consequences can be so serious. The question should be “Can you drive safely?,” not “Have you been drinking?”.

Alcohol testing also doesn’t do anything to get people off the road who are using illegal drugs, or legal prescriptions that may cause drowsiness, or working triple shifts in the local factory or hospital. Is there an argument to be made that blood testing should be replaced by some kind of standardized performance testing? Is such equipment commercially available? Would this be a fairer system?

I’m in no way defending drunken driving. But the reason for locking people up who exceed a specified blood alcohol level is the presumption that they are dangerous drivers. If that’s not true, they shouldn’t go to jail. I wonder whether it would make more sense to alter the charge to something like Driving While Impaired, and the legal question would be whether or not someone was actually able to drive safely, not whether he had imbibed alcohol.

The presumption of impairment is the reason the law was enacted setting the limit where it is. However, once the law is passed a violation is a violation. It isn’t a deep dark secret that there is a law that presumes impairment at some particular level.

As a recovering alcoholic who drove with an illegal blood alcohol level many times I don’t worry about unfairnes to those who drive with blood alcohol over the legal limit whether or not they are impaired.


Like what? The first step to a DUI is to drive in a manner indicating you may be intoxicated/on drugs. The second test is to fail one or more of the field sobriety tests, which are themselves a form of “standardized performance testing.” The third step is to blow a .08 or more on a field sobriety test and the fourth step (in my jurisdiction) is to again blow a .08 or more on the breathalyzer at the police station. (The fifth step is to be booked into the jail.) So there is already standardized performance testing, including but not limited to the eye nystagmus test, tests of balance, and tests of the subject’s memory and ability to follow commands. There is also the officer’s “experience and training,” which are also of some weight when a DUI arrest is challenged.

The problem is that there is no way to prove the point at which each individual becomes a dangerous driver. The law must be applied to everyone, and applied in a way that is both facially and substantively fair – the same law, applied in the same manner, to everyone. So, yes, the presumption of impairment at .08 is just that, a presumption. Heck, it used to be .10 for years, until most jurisdictions lowered it. That obviously doesn’t mean a person blowing a .08 is magically drunker at .08 than he or she used to be. You are certainly correct that there is a presumption of impairment at that level, and further correct to conclude that the presumption will not hold true in every single case. But that’s the line we as a society have chosen to draw, and since there is no better realistic way to test impairment, that’s what we go with. It’s a far sight better than before breath tests, when the entire DUI case rested on the officer’s subjective opinion on how the person was behaving or did on the tests. Such opinions are easily attacked, whereas it’s hard to argue with a machine that spits out a card that says “.09.”

The question is not whether the driver had imbibed alcohol, but whether he or she has imbibed a sufficient quantity of alcohol to be presumptively impaired. So they are checking for impairment, not for alcohol consumption – blow less than a .08, and you’re back on your merry way. But since there is no way to check the impairment of every individual, we as a society have decreed that at a certain level impairment will be presumed. I freely admit the deficiency you’re pointing up – not everyone will actually be impaired at that level – but I see no way to correct it.

The one thing your post suggests, however, is that a refinement of the system might be to institute a different levels for presumptive impairment based on factors such as gender or size. The truth is that the government probably couldn’t get away with that, based on due process concerns, and trying to enforce a sliding scale would be a nightmare. (“Let’s see, you’re a woman, but you weigh 250 pounds and you’ve been drinking since you were 12 . . . I don’t see that on my chart.”)

What about sobriety checkpoints? I have no problem with “the first step” being a driver swerving all over the road. But, in my part of the world sobriety checkpoints exist.

Observer, I read the same article and came away with a really bad taste in my mouth about the whole thing. Like the woman who never drinks, and who had one drink, and was thrown in jail. No license for a year. Her life fell apart after that. That being said, however, I had to question…how could someone be above .08 after one drink, several hours after last call? You will note the article says she was arrested at 4:30 am…

The question of people “lowballing” how much they had to drink was brought up in the live online chat yesterday: It seems to me many people in the story way lowballed how much they had to drink…

Is blood alcohol level alone a fair measure of impairment? No, but it’s the most objective standard available, hence the laws use blood alcohol level as their criterion. If I had a dime for every time someone swore they could “hold their liquor”, I could retire.

I think it’s fair, despite the fact that it’s not completely accurate. You have to balance the desire to be accurate (i.e., do the “right thing” in each particular case) with the fact that you need some practical way of enforcing the law.

If you think about it, there are many instances in which the law imposes a general standard, even though it might not be quite right for every situation. Consider speed limits, for instance. On a given stretch of highway, there are probably some drivers who can control their vehicle quite well at 80 miles per hour, and some others who are dangerous at 50. But it’s just not workable to have individual speed limits for everyone, so we pick a number and make everyone stick to that.

I don’t think this argument is very strong unless you can propose a test that (1) is significantly more accurate than measuring blood alcohol level, and (2) can practically be administered by a police officer by the side of the road. I can’t think of such a test off the top of my head; the only alternative I know of is the “hop on one foot” type of thing, and I don’t believe that’s considered any more accurate than blood alcohol level.

Right, and how many times have you stopped at a stop sign when you were the only vehicle in sight.

I can’t stand long on one foot let alone hop and have difficulty walking a staight line and I haven’t had a drink of alcohol for 22 years.

I was going to post something along the lines of what TJVM posted about speed limits. There’s a lot of fixed numbers in the law (and not just regarding driving) all of which makes things much more objective and less subjective.

In addition to speed limits:

(Most states have 15 for learners, 16 for full license.) So if you’re 16 years - 1 day you can’t drive by yourself but one day later you can. Surely there are many types of people where they are good drivers at 15 but other types that aren’t good drivers still at 18. Is there discrimination going on there?

You can vote at age 18. Some 16 year olds know a lot more (and care more) about politics than many 50 year olds.

You can drink at 21. Same thing. Should those groups who “can’t hold their alchohol” have higher drinking ages?

In short, the kind of “logic” the OP refers to is just lawyer glurge. They throw this at jurors hoping to get the client off.

RE: The lady who had one drink.

It is very possible she had a Long Island or something like a 32oz Rum Runner. Something she considered “one drink” because it comes in one cup. But it contains way more than one drink worth of alcohol.

There is an issue here I don’t understand.

Take this theoretical example. I go out with my twin brother, we are both 23, both 150 lbs, both the same genetics, ect…

The difference is, I have never had a drink before, where as he has had a six pack a night for three years.

We both drink four beers.

I am now falling down drunk, he is not even buzzing.

On the way home, we get pulled over.

We blow. Will we have the same BAC?

Does ‘tollerance’ mean you get the alcohol out of your system faster, or does it mean your system is better able to keep you sober with it in your system?

Both. A heavier drinker will, to a point, be able to eliminate alcohol from the blood stream slightly faster than a non-drinker, but not by much.

However, heavy drinkers/alcoholics can show a remarkable ability to cope with higher BAC levels than non-drinkers. For example, working with a fire-rescue rescue, I’ve seen people that blew a BAC of .316 that I could barely even tell were obviously drunk. At .08, their level of motor impairment would probably be minimal compared to someone who had never had a drink before, while at .316 you or I would most likely be dead or comatose. IF anything, these standards are unfair to people that have adapted to continually high BAC levels, but I fully agree with everything that has been said about needing a defenite cut-off point for this behavior.

“Tolerance” means that your body is used to having so much alcohol in it and manages function somewhat better that some one with no tolerance to alcohol.

The amount of alcohol in your blood is a function of how much you drink in how much time, how much blood you’ve got to thin it with (more bodyweight=more blood=lower BAC on the same volume of alcohol,) and how fast your body can metabolize and eliminate alcohol.

That wouldn’t work because people who have been drinking tend to overestimate their ability to drive.

I recall a Swedish (Norweigan?) study from a year or three backthat basically said “yes, people can learn to do tasks (well) while drunk.” Tried to google for the study but I couldn’t find it.

Is there a sliding scale for drunk driving penalties in most states? It seems appropriate that someone with a 0.25 BAC (probably extremely trashed) gets a heftier penalty than someone with a 0.085 BAC (barely above the legal limit.)

Is a person’s blood alcohol level necessarily a fair measure of impairment? The answer is no but that’s not really the point anymore.

A short history is required. We all know about how in the 1970s and 1980s an upstart organization called Mothers Against Drunk Drivers (“MADD”) very successfully pushed to have very much tougher laws prohibiting drunk driver put in place and then rigorously enforced. Their first effort was based on the blood alcohol test. This was sold to the legislatures as a scientifically based objective measurement that a person was too drunk to drive. If a person blew into the breath machine and his reading came up too high (usually 0.10 percent) then this was introduced in court as prima facie evidence that the person was engaged in drunk driving.

The problem from MADD’s perspective, and from the police and D.A.'s perspective, was that the drivers and their clever defense lawyers fought back and very often won in court. The defendants submitted objective evidence in trial that showed that the person wasn’t too drunk to driver, no matter what the stupid breath-test machine said. The defendants used persuasive evidence like the defendant’s neat and legible signature on the paperwork he signed at the police station at the time of his arrest, or his neat appearance at the police station, or his clear speech pattern, or even his driving itself (ie, “Sure he was speeding and the cop had the right to stop him for that, but the defendant pulled over right away when he saw the cop and brought the car to a safe and smooth stop in the parking lot right between the lines, and didn’t stumble when he got out of the car and didn’t fumble for his driver’s license when asked to produce it, so his driving wasn’t really impaired”) etc. Many drivers were found not guilty of drunk driving even though they tested over the limit that allegedly objective science said should have been too high to drive safely.

As a result of that, MADD, the police and the prosecutors pushed for and won changes in the criminal statutes. Now, a person can be charged both with drunk driving and with the separate offense of driving with a blood alcohol level over the legal limit. The second offense isn’t concerned with whether the person was too drunk to drive or not. It statutorily skips that test as being too hard to prove and just makes it an offense to drive with, or even sit in parked car with the key in the ignition with, or ride a bicycle with, a blood alcohol level over the prohibited amount, which is now 0.08 percent in most US states. The question now is not whether blood alcohol level is a fair measure of impairment, it is whether blood alcohol level alone is a fair test to base a severe criminal statute on.

I say it isn’t, but if I was a craven politician with a MADD mother threatening to run ads against me calling me soft on drunk driving I’d probably say otherwise.

Let me emphasize again that I am not defending drunken driving. In fact, I would like to see tougher sentences for repeat offenders. But what I was getting at in my first post is that most of the people profiled in the Post article were not hard-core drunks stumbling out of bars at closing time and climbing behind the wheel. Many were not even regular drinkers, so they didn’t have the experience base to know how much they were being affected. The point is that a drinker doesn’t know that he is at the .08 limit until he is tested, and who is equipped to test himself? A few bars may have party-style breath testers, but by most accounts they are not accurate, and they are rare in any case. A casual drinker doesn’t know his blood alcohol level is illegal until the trooper is slapping the cuffs on him. In other words, even though the standard is theoretically objective, no individual person can be sure that he in in compliance with the law. A truly objective standard would be something like, “If you drink more than two ounces of alcohol in any form in any one-hour period, you may not operate a motor vehicle for four hours.” Every person who could count to two and four could understand and apply that law, and it would apply equally to everybody. Maybe places that sell alcohol should be required to offer the use of a commercial-grade breathalyzer to their patrons, or maybe there could be coin-operated breath testers in parking lots and garages. Or maybe police should set up breathalyzers outside hot nightspots, with the understanding that failing would not have legal conseqences as long as the drinker didn’t try to drive. Add into the equation the impact of differences in physical size, gender and ethnicity. A 250-pound white male can belt down a bucket of beer and drive home, and a tiny Vietnamese woman goes to jail after one drink. A inexperienced drinker can also be sucker-punched by a “dessert drink.” A pina colada tastes like fruit juice and an Irish cream like a milk shake, and it’s easy (however colossally stupid) to treat them that way. My point is that willful intent is usually an element of a criminal conviction, and a lot of these people literally couldn’t know they were violating the law.

It also disturbing to note that almost everyone got the same penalty, regardless of their individual circumstances. For a first offender, blowing .085 gets the same punishment as .29. Comparing it to speed limits is actually quite useful. If the speed limit is 55 mph, you are breaking the law when you hit 55.1. But most of the time a cop won’t even notice you at 5 over, unless he has another reason to stop you. After that, the penalties usually increase in steps. Up to 10 mph over the limit might get a fine and points. 10 to 19 gets a bigger fine and more points. More than 20 is worth still more money and points, and can even result in a reckless driving charge, which you might be able to dispute depending on the specific circumstances. The point is that the penalty is commensurate with the violation. By comparison, treating everyone who blows .081 on an alcohol test as a dangerous criminal is like charging everyone who drives 57 in a 55 with reckless driving. There’s no reason why drinking penalties shouldn’t be stepped the same way. We pay judges to make judgments. If we are going to put everybody on the same assembly line we may as well put the prosecutor in charge.

The link cited above to a web chat with the authors of the Post story is worth visiting for a wide range of views. Some people wrote about terrible tragedies that drunk drivers have inflicted on their families. Others wrote about losing their licenses because they requested a blood test rather than a breath test, and the officer interpreted that as a refusal to be tested at all. A prosecutor said that the jails are already so overcrowded that people who belong there are getting probation, and tougher driving penalties make the situation worse. It’s worth reading:

As a fairly bulky and generally responsible male, I’m not worried that having a beer at a ball game is going to ruin my life. And I have no sympathy for habitual drunks. But the really dangerous people seem to be crafty enough not to get caught, and people who make a stupid mistake are getting sucked into an unforgiving system.

I thought that the really dangerous people died, and took others with them. The “one drinker’s” were unfortunate, one can be “under the influence” without “driving while intoxicated”. This is a numerical difference.

I think we’ve established that physical ability to operate a car cannot be quantified by a numeric equivalent as far as alcoholic impairment goes. A comic once said" The reason we have such a problem with drunk driving, is because people don’t know how to drive drunk!" There is a bit of truth to this. Nobody should ever drive drunk, but some people are better than others at driving with a higher BAC.

The BAC% system is obviously flawed, but it errs on the side of caution. I can appreciate that, but, a person’s ability to drive a car safely is not solely dependent on their BAC. I’d rather ride with one of my friends while a bit tipsy, than another of my friends when she’s talking on her damn cell.

Where I live you can be ticketed for DUI and DWI separately. It seems to me that if I have 1 light drink at a bar or restaurant, I am instantly violating a statute by driving home (I would be DUI whether or not I was over the limit). Why then would any establishment that serves alcohol have a parking lot? For the DD’s only? Bullshit.

I think every drunk driver (drivers that were actually drunk) should get a shame plate on their car. In Ohio it’s a yellow and orange plate, it let’s the cops know who’s been naughty last year. Make them feel bad for crossing the line, just don’t impair their ability to go to work.

I think it would be workable to have individual BAC limits, though. Just print it on your driver’s license.

The problem with individual speed limits is a police officer can’t tell whether someone going 80 in a 60 zone is legally allowed to do it. He’d have to pull them over, check their license, and either give them a ticket or apologize and send them on their way. Every moment he spends pursuing a speeder who turns out to be speeding legally is a moment he isn’t pursuing someone who’s actually breaking the law.

But BAC is only an issue (1) when someone has been driving erratically, in which case the decision is whether to ticket them for DUI or for reckless driving, or (2) at a sobriety checkpoint, where everyone is checked anyway.

I’m not too concerned with the inequality in the OP, but I do have some sympathy for Adam Carolla’s proposal that since he’s a “heavyweight”, he ought to be able to take a driving test while he’s drunk, thereby becoming legally able to drive with a higher BAC than the rest of us lightweights.


BAC is not an accurate measure of impairment. There was a show on The Discovery Channel where a researcher measured BAC along with motor skill/reaction times and some with a BAC below the legal limit were sufficiently impaired while others considerably above the limit were not. The latter group are the ones that get fucked by BAC tests because most people assess their BAC by how drunk they “feel.” Some sort of physical/mental task impairment task would be much better. I wouldn’t be surprised if some tee-totalers failed that one though. Of course, maybe that’s not a bad thing.