# Is blood alcohol level alone a fair measure of impairment? **URL:** \ **Category:** Factual Questions\ **Created:** [July 27, 2004, 4:38am UTC](https://boards.straightdope.com/t/is-blood-alcohol-level-alone-a-fair-measure-of-impairment/257049 "2004-07-27T04:38:30Z")\ **Posts on this page:** 14\ **Page:** 2
**Author:** ![Loach](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/loach/32/350_2.png) [@Loach](https://boards.straightdope.com/u/Loach)\ **Post date:** [July 29, 2004, 4:04pm UTC](https://boards.straightdope.com/t/is-blood-alcohol-level-alone-a-fair-measure-of-impairment/257049/21 "2004-07-29T16:04:12Z")
> [@](#): > > 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. But would you be driving erratically? Have the strong smell of an alcoholic beverage? How is your horizontal gaze nystagmis? Is your speech slurred? Can you find your wallet? Do you know what time it is? Do you know where you are? Where you are going? If you start to hop you won’t be arrested. I hope you were exagerating for effect. A DWI arrest is based on the totallity of the circumstances not one test. Someone please show me how any adult can get a BAC of .1 or .08 after one standard drink. I am not talking about breath alcohol. Lets assume a blood test. Its not possible as far as I know. I have seen adults drink the usual “I had 2 beers”. It barely registers. Maybe a .01 for an average adult male. This isn’t voodoo its science. I wish I had the formulas for computing BAC handy but I don’t ☹ ---
**Author:** ![threemae](https://avatars.discourse-cdn.com/v4/letter/t/5f9b8f/32.png) [@threemae](https://boards.straightdope.com/u/threemae)\ **Post date:** [July 29, 2004, 5:32pm UTC](https://boards.straightdope.com/t/is-blood-alcohol-level-alone-a-fair-measure-of-impairment/257049/22 "2004-07-29T17:32:52Z")
> [@Loach](#): > > But would you be driving erratically? Have the strong smell of an alcoholic beverage? How is your horizontal gaze nystagmis? Is your speech slurred? Can you find your wallet? Do you know what time it is? Do you know where you are? Where you are going? If you start to hop you won’t be arrested. I hope you were exagerating for effect. A DWI arrest is based on the totallity of the circumstances not one test. > > Someone please show me how any adult can get a BAC of .1 or .08 after one standard drink. I am not talking about breath alcohol. Lets assume a blood test. Its not possible as far as I know. I have seen adults drink the usual “I had 2 beers”. It barely registers. Maybe a .01 for an average adult male. This isn’t voodoo its science. I wish I had the formulas for computing BAC handy but I don’t ☹ .01? No. Two beers will most certainly put most anyone at least in the .05-.06 range if not higher. Of course, this speaks nothing to impairment, but definitely isn’s a .01. Cite: [http://www.health.org/nongovpubs/bac-chart/](http://www.health.org/nongovpubs/bac-chart/) ---
**Author:** ![David\_Simmons](https://avatars.discourse-cdn.com/v4/letter/d/9de053/32.png) [@David\_Simmons](https://boards.straightdope.com/u/David_Simmons)\ **Post date:** [July 30, 2004, 4:31am UTC](https://boards.straightdope.com/t/is-blood-alcohol-level-alone-a-fair-measure-of-impairment/257049/23 "2004-07-30T04:31:45Z")
> [@Loach](#): > > But would you be driving erratically? Have the strong smell of an alcoholic beverage? How is your horizontal gaze nystagmis? Is your speech slurred? Can you find your wallet? Do you know what time it is? Do you know where you are? Where you are going? If you start to hop you won’t be arrested. I hope you were exagerating for effect. A DWI arrest is based on the totallity of the circumstances not one test. > > Someone please show me how any adult can get a BAC of .1 or .08 after one standard drink. I am not talking about breath alcohol. Lets assume a blood test. Its not possible as far as I know. I have seen adults drink the usual “I had 2 beers”. It barely registers. Maybe a .01 for an average adult male. This isn’t voodoo its science. I wish I had the formulas for computing BAC handy but I don’t ☹ Of course, hopping and walking a straight line aren’t the only possible tests and aren’t they only performance tests given. My point, badly explained, is that there is no system that isn’t flawed if poorly executed. And I’ll say it again. Fair or not, the fact that driving with blood alcohol 0.08 or more is illegal in most states whether or not that results in impairment and that fact isn’t a deep dark secret. That doesn’t leave many “outs” for those who persist in doing it. ---
**Author:** ![David\_Simmons](https://avatars.discourse-cdn.com/v4/letter/d/9de053/32.png) [@David\_Simmons](https://boards.straightdope.com/u/David_Simmons)\ **Post date:** [July 30, 2004, 4:35am UTC](https://boards.straightdope.com/t/is-blood-alcohol-level-alone-a-fair-measure-of-impairment/257049/24 "2004-07-30T04:35:05Z")
> [@David Simmons](#): > > Of course, hopping and walking a straight line aren’t the only possible tests and aren’t they only performance tests given. My point, badly explained, is that there is no system that isn’t flawed if poorly executed. > > And I’ll say it again. Fair or not, the fact that driving with blood alcohol 0.08 or more is illegal in most states whether or not that results in impairment and that fact isn’t a deep dark secret. That doesn’t leave many “outs” for those who persist in doing it. My blood alcohol level is close to zero after 22 non-drinking years and I still failed a performance test. This sentence, “Of course, hopping and walking a straight line aren’t the only possible tests and aren’t they only performance tests given.” should read, “Of course, hopping and walking a straight line aren’t the only possible tests and aren’t **the** only performance tests given.” ---
**Author:** ![observer](https://avatars.discourse-cdn.com/v4/letter/o/47e85d/32.png) [@observer](https://boards.straightdope.com/u/observer)\ **Post date:** [July 30, 2004, 5:25am UTC](https://boards.straightdope.com/t/is-blood-alcohol-level-alone-a-fair-measure-of-impairment/257049/25 "2004-07-30T05:25:20Z")
Some other factors that can affect blood alcohol level: [http://www.silcom.com/~sbadp/effects/bac.htm](http://www.silcom.com/%7esbadp/effects/bac.htm) A blood alcohol estimator: > **[Intoximeters Drink Wheel to Measure Blood Alcohol Content](https://www.intox.com/drink-wheel/)** > > The Intoximeters "Drink Wheel" is a form that you can fill out that when completed will instantly compute your estimated blood/breath alcohol concentration ("BAC") or blood alcohol content. This simulates the breath alcohol testing done by an... A blood alcohol chart: [http://www.health.org/nongovpubs/bac-chart](http://www.health.org/nongovpubs/bac-chart) Note that two\* standard\* drinks will tip a 100-pound woman over the line, and remember that many establishments pride themselves on serving “generous” portions. There also seems to be some evidence that breath testing is not entirely reliable. Some non-alcohol factors will increase the reading, including breath byproducts of dieting and diabetes and digestion of certain foods, body temperature, air temperature and size of air sample. And if you are stopped and demand a blood test, universally recognized as more accurate than a breath test, the cop might write you up as refusing to be tested. [http://www.duicenter.com/books/dd\_book/chemical.html](http://www.duicenter.com/books/dd_book/chemical.html) [http://www.california-drunkdriving.org/breathalyzer\_tests/](http://www.california-drunkdriving.org/breathalyzer_tests/) [http://www.forensic-evidence.com/site/Biol\_Evid/Breath\_Tests.html](http://www.forensic-evidence.com/site/Biol_Evid/Breath_Tests.html) [http://www2.potsdam.edu/alcohol-info/DrivingIssues/1055505643.html](http://www2.potsdam.edu/alcohol-info/DrivingIssues/1055505643.html) Links to other information sources: [http://guides.california-drunkdriving.org/blood\_alcohol.html](http://guides.california-drunkdriving.org/blood_alcohol.html) Drunk driving is very bad. Nobody should ever do it. But the bottom line is that this field is full of variables, which the legal system doesn’t seem willing to recognize. ---
**Author:** ![Jodi](https://avatars.discourse-cdn.com/v4/letter/j/7feea3/32.png) [@Jodi](https://boards.straightdope.com/u/Jodi)\ **Post date:** [July 30, 2004, 5:51am UTC](https://boards.straightdope.com/t/is-blood-alcohol-level-alone-a-fair-measure-of-impairment/257049/26 "2004-07-30T05:51:53Z")
> [@](#): > > But the bottom line is that this field is full of variables, which the legal system doesn’t seem willing to recognize. How, exactly, is the legal system supposed to recognize all those variables? Recall that the law must be applied equally to everyone or it will draw a challenge that it is unconstitutional (facially or as applied, probably both) because it violates the Equal Protection clause. The existing system rests on a legal fiction that everyone over a certain level is deemed drunk – they are, in effect, drunk as a matter of law. Fail to reach that limit and you’re okay; exceed it, and you’re not. Same line, drawn in the same place, for everyone. Your argument appears to be that some of those people are not actually drunk. But there is no practicable way to establish that on an individual basis, just as there is no practicable way to determine each individual’s safe driving speed, which is why we have speed limits that effectively determine as a matter of law the point at which your driving is presumptively unsafe. A person’s awareness of his or her limitations is irrelevant; you cannot exceed the limit (whatever it may be), and if you are reduced to guessing about whether you are over it or not, then you live with the consequences when and if you guess wrong. ---
**Author:** ![TeaElle](https://avatars.discourse-cdn.com/v4/letter/t/8491ac/32.png) [@TeaElle](https://boards.straightdope.com/u/TeaElle)\ **Post date:** [July 30, 2004, 10:29am UTC](https://boards.straightdope.com/t/is-blood-alcohol-level-alone-a-fair-measure-of-impairment/257049/27 "2004-07-30T10:29:07Z")
> [@nyctea scandiaca](#): > > 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 Perhaps because as a small Asian woman who didn’t drink regularly, her body wasn’t able to metabolize the alcohol she consumed. If there was some case for challenging the validity of her BAL, I’m sure her lawyer would have done so. It’s not as if she was pulled over on a whim, she was driving erratically, and pulled over because of that. If the officer hadn’t had reason to suspect that she was impaired, intoxicated or otherwise incapable of driving safely, there would be no reason for her to have been stopped to begin with. But that case points out why MADD and other safety proponents aren’t against **drunk driving** , they’re against **drinking and driving**. The motto is “impairment begins with the first drink” and the standard is that if you have had any alcohol, you do not operate a motor vehicle, and if you’re going to have to operate a motor vehicle, you do not have any alcohol. If you choose to drive after imbibing, you’re running the risk of facing criminal penalties. You have to weigh the options and make the choice that most appeals to you – having a drink and risking jail or staying sober and staying free. > [@observer](#): > > 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. There’s also **negligence**. A failure of due diligence is just as damning as a specific willful intent. In the case of drunk driving, while someone can argue that they “didn’t know” that their BAL was over the legal limit and that they “didn’t intend” to be impaired and/or intoxicated, they cannot argue if they sat and drank alcohol and then got behind the wheel of a car that they did not do everything that they could to avoid driving under the influence of an impairing intoxicant. > [@dnoonan](#): > > 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. Wow, leap of logic much? Yes, you can be in violation of the statute by driving home after one drink. If you’re not violating the motor vehicle laws when you do so, you’ll never have to face the penalty for that crime. Impairment _is_ a component of the crime, it is the reason why you are stopped in the first place. And as for the parking lot red herring – should no one drive to any restaurant, say the local Olive Garden, because they serve alcohol, so even the non-drinkers like myself are inconvenienced because of people who cannot control their drinking or have overstated opinions of their ability to drive after drinking? That makes no sense. > [@Mr2001](#): > > I think it would be workable to have individual BAC limits, though. Just print it on your driver’s license. Uh huh, and how is that supposed to be determined? If you want to drink, you’ve got to go to some center and be tested to see how impaired your motor skills and judgment making capabilites are at certain points of consumption? What happens when you gain or lose 30 pounds? Or have a temporary bout with insomnia? Or take meds for your seasonal allergies? Or start taking birth control pills? Or switch from your usual scotch and water to scotch and soda? ---
**Author:** ![Loach](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/loach/32/350_2.png) [@Loach](https://boards.straightdope.com/u/Loach)\ **Post date:** [July 30, 2004, 1:37pm UTC](https://boards.straightdope.com/t/is-blood-alcohol-level-alone-a-fair-measure-of-impairment/257049/28 "2004-07-30T13:37:36Z")
> [@](#): > > .01? No. Two beers will most certainly put most anyone at least in the .05-.06 range if not higher. Of course, this speaks nothing to impairment, but definitely isn’s a .01. Bullshit. “Most certainly” should be changed to maybe, possibly under very unrealistic and controlled circumstances. When was the last breathalyzer class that you took? That is a scare chart without any scientific backing. _Maybe_ if you shotgun two beers and take a test right away your BAC might be elevated. It does not properly take into account one of the most important factors in BAC, time. We have demonstrators (drunks) during every class. The machines are claibrated before the class for accuracy. Two of the drinkers have 2 (American) beers over a couple hour period. Several others were drinking heavily. The 2 beer guys hardly registered. If you tell me you were at the bar all night and had two beers and blow a .08 then I know you are lying. The [link](http://www.intox.com/wheel/drinkwheel.asp) that observer gave seems to give a more realistic estimation of BAC. Of course the less you weigh the higher your BAC will be with fewer drinks. 2 beers over 2 hours for a 180 lb male and your BAC will be .003. There are other factors involved in how fast alcohol is absorbed: > [@](#): > > Factors that will affect the BAC in a person: > > How much alcohol you drink. > How fast you drink. The quicker you drink, the higher your peak BAC will be. The liver gets rid of alcohol at the average rate of one drink per hour (12 oz. beer, 5 oz. wine, 1 shot of distilled liquor). If a person drinks faster than this, the r emainder will circulate in the blood stream until the liver can get rid of it. > Body weight. Heavier people will be less affected by the same amount of alcohol than lighter people. They have more blood and water in their bodies in which to dilute the alcohol. > Food in the stomach. When there is food in the stomach, alcohol is absorbed slower into the blood stream. The BAC rises more rapidly in those who drink on an empty stomack, because there is no food in which to dilute the alcohol. > The type of alcohol you drink. The stronger a drink is (the higher the alcohol concentration, distilled alcohol first, wine second, beer third) the more quickly it is absorbed. This partially explains why hard liquor has more of an apparent “ kick” than wine or beer. > Type of mixer used. Water and fruit juices mixed with alcohol slow the absorption process, while carbonated beverages will speed it up. Carbon dioxide speeds the alcohol through the stomack and intestine into the bloodstream, creating a rapid rise in BAC. > Temperature of the drink. Warm alcohol is absorbed quicker than cold alcohol. > If you are male or female. Women reach higher BAC’s faster because they have less water in their bodies and more adipose tissue (fat), which is not easily penetrated by alcohol. Therefore, a man and woman, with all other factors being equal, both drinking the same amount of alcohol will have different BAC levels. Hers will be higher. A woman’s menstrual cycle will also affect her rate of absorption. They will experience their highest BAC’s premenstrually. In addition, there is a lso evidence that a woman taking birth control pills, will absorb alcohol faster, resulting in higher BAC levels. Just for the record. I have never seen anyone who is at .08 or higher who is not impaired in some way. I have seen people (mostly non-drinkers) at .05 who shouldn’t be on the road. The level of impairment changes but .08 is a high enough level that no one should be driving. > [@](#): > > Some non-alcohol factors will increase the reading, including breath byproducts of dieting and diabetes and digestion of certain foods, body temperature, air temperature and size of air sample. And if you are stopped and demand a blood test, universally recognized as more accurate than a breath test, the cop might write you up as refusing to be tested. If you go into court with your doctor and he testifies that you were going through a diabetic emergency you are going to get off. A diabetic may smell (due to ketones on his breath) like he is drinking and act drunk due to his condition but it will not show up on a breathalyzer the same way. I have seen a film of a sobriety test given to a DWI suspect. The subject failed miserably and was a very funny drunk. The instructor asked us to guess what the reading was. We all guessed in the .2 to .3 range. The guy blew a .000. He was diabetic and the breathalyzer showed he had no alcohol in his blood. Most factors that change breath BAC will _lower_ the reading, not raise it. A breathalyzer has a certain sized air chamber. It is not very big. If you do not fill the chamber its a refusal. Its very easy to tell if the sample is not big enough. The time of the test is recorded. The test must be given after a time period has passed in order to ensure that nothing is in the mouth which will throw off the reading. As to the blood test, it depends on what state you are in. In Pennsylvania there is no breath test. They take you to get blood drawn. Most cops would prefer this but I don’t know of any other states that do it, though there might be. In New Jersey there is an implied consent law. If you have a driver’s license then you have already consented to give breath samples. It is not up to you to determine probable cause. The cop has to prove there was PC at trial but you can not refuse to give a sample. If you do its a separate charge. After the breath tests are given then you have the right to go to a doctor and get blood drawn if you would like. Whatever weight that test is given will be up to the judge. In my experience judges will quickly throw out a breath test if the defense can prove that there is anything wrong with the machine or the test procedures. The newer breathalyzers have gone through rigorous scientific and legal testing. They are a lot more cop proof than the old ones so most of the procedural defense arguments have been taken away. Now they mostly attack PC. Remember one thing: The laws in every state vary greatly. I know mostly about New Jersey. And if you think the laws in America are Draconian, try looking at Europe and the rest of the world and see what their penalties are. ---
**Author:** ![Loach](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/loach/32/350_2.png) [@Loach](https://boards.straightdope.com/u/Loach)\ **Post date:** [July 30, 2004, 1:45pm UTC](https://boards.straightdope.com/t/is-blood-alcohol-level-alone-a-fair-measure-of-impairment/257049/29 "2004-07-30T13:45:01Z")
In the above post I undelined the word _most_ because of course a lawyer can find a way to argue anything 😉 . I just tried to emphasize that the new machines are a lot easier to use and more reliable. Some of the old machines are 40 years old and break often. I have seen a lot of cases thrown out because of old machines. If it breaks then all of the cases since the last official accuracy check get thrown out. ---
**Author:** ![Finagle](https://avatars.discourse-cdn.com/v4/letter/f/b19c9b/32.png) [@Finagle](https://boards.straightdope.com/u/Finagle)\ **Post date:** [July 30, 2004, 3:27pm UTC](https://boards.straightdope.com/t/is-blood-alcohol-level-alone-a-fair-measure-of-impairment/257049/30 "2004-07-30T15:27:22Z")
For the borderline cases (such as the asian woman who supposedly blew a 0.08 after one drink), why is it not a defense strategy to argue that the law specifies a specific numeric limit, but, seeing as human beings don’t have gauges, there’s no way for normal person to determine whether they are at that limit or not? Or to phrase it somewhat differently, if people differ idiosyncratically in their reactions to alcohol and blood alcohol level, to the point where charts and rules-of-thumb are inaccurate, how can you penalize them for not knowing the unknowable? It’s sort of like removing the speedometer from cars and then saying “Don’t speed.” ---
**Author:** ![muttrox](https://avatars.discourse-cdn.com/v4/letter/m/a8b319/32.png) [@muttrox](https://boards.straightdope.com/u/muttrox)\ **Post date:** [July 30, 2004, 5:28pm UTC](https://boards.straightdope.com/t/is-blood-alcohol-level-alone-a-fair-measure-of-impairment/257049/31 "2004-07-30T17:28:09Z")
I am no expert on any of this. I believe that when the actual limit was set, it was set rather conservatively for just this reason. That is, the legislators thought that most people are impaired at .05, but they initially set the limit at .12, just to make sure that anyone who was that high was virtually certain to be impaired. I guess the analogy would be setting the speed limit at 95 on a road that is clearly designed for 40. Anyone who got caught driving at 96 would almost certainly be driving unsafely, because the limit was set so conservatively. Anyone know more about that?, I don’t have any cites. ---
**Author:** ![Loach](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/loach/32/350_2.png) [@Loach](https://boards.straightdope.com/u/Loach)\ **Post date:** [July 30, 2004, 5:59pm UTC](https://boards.straightdope.com/t/is-blood-alcohol-level-alone-a-fair-measure-of-impairment/257049/32 "2004-07-30T17:59:47Z")
Just made a long reply and the squirrels ate it :mad: . If I stop being angry I might write it again. Until then I give you the DWI law from [New Jersey](http://nj-dmv-dwi.com/parts/dwilaw.html) in case you would like to look at it. ---
**Author:** ![zamboniracer](https://avatars.discourse-cdn.com/v4/letter/z/e9a140/32.png) [@zamboniracer](https://boards.straightdope.com/u/zamboniracer)\ **Post date:** [July 31, 2004, 4:12pm UTC](https://boards.straightdope.com/t/is-blood-alcohol-level-alone-a-fair-measure-of-impairment/257049/33 "2004-07-31T16:12:23Z")
I’ve been thinking about this and I think making a crime out of a driver’s level of alcohol to blood-breath-or-urine has outlived its usefulness. Police cars and police stations all have TV cameras now that routinely film all police stops and all conduct at the station. The camera never lies, unlike several witnesses and police officers I could name (and assuming Steven Speilberg doesn’t have access to the cameras!). Just tape everything and let the judge and jury make the decision about whether the driver was too drunk to drive or not, or whether there was probable cause to arrest or not. ---
**Author:** ![Jodi](https://avatars.discourse-cdn.com/v4/letter/j/7feea3/32.png) [@Jodi](https://boards.straightdope.com/u/Jodi)\ **Post date:** [August 1, 2004, 2:40am UTC](https://boards.straightdope.com/t/is-blood-alcohol-level-alone-a-fair-measure-of-impairment/257049/34 "2004-08-01T02:40:56Z")
> [@](#): > > Police cars and police stations all have TV cameras now that routinely film all police stops and all conduct at the station. This is not accurate. If there is routine filming at the station, it probably will be of the booking area only, not “all conduct at the station.” Some stations don’t even film booking, since having everything on tape is a two-edged sword (it can be used against the cops as easily as the suspect, if the cops are alleged to have misbehaved or to have screwed something up). Further, cameras in squad cars are expensive. Some law enforcement agencies may have only some of their cars camera-equipped; small and/or rural law enforcement agencies (with small budgets) may not have cameras in the cars at all, because they can’t afford them or think it’s more important to buy other equipment first. [Previous page](https://boards.straightdope.com/t/is-blood-alcohol-level-alone-a-fair-measure-of-impairment/257049.md?page=1)