Dispatches from the Creation Wars


Here’s an interesting blog with very valuable information about the highly dubious nature of breathalyzer tests and why, frankly, they should be inadmissable in court (and this from a guy who rarely drinks and never drinks and drives). Breathalyzer tests do not measure the presence of alcohol, they measure the presence of methyl compounds. They then multiply the concentration of such compounds in your breath by 2100, which is a calculation of how much alcohol would be in an average person’s bloodstream if it is found in such concentrations in one’s breath.

It’s not difficult to see the problems with such a measurement. First, methyl compounds are found in many other substances other than alcohol and are even produced by the body itself (especially for diabetics). Thus, exposure to or ingestion of non-alcoholic substances which contain methyl compounds can give a falsely high reading. Second, the rate at which the human body metabolizes alcohol varies widely from person to person, making the average calculation highly inaccurate in many cases. Enough so that the margin for error for a breathalyzer test, according to the manufacturers, is a full 20%. And yet this is the sole evidence used to convict drunk drivers even without any confirmation that they were driving badly or a risk to anyone. So much for “beyond a reasonable doubt.”


  1. #1 coturnix
    February 21, 2006

    Not to mention no controlling for body size, for sex differences in alcohol metabolism, or for circadian variation in alcohol metabolism (which is huge – that is why we drink in the evening, as a single beer at dawn will make you very drunk).

  2. #2 Susan Brassfield Cogan
    February 21, 2006

    I probably varies from state to state, but I believe you don’t have to accept the breathalyzer. You can demand a blood test. And for those with a guilty conscience, you will be detoxing the entire time they are transporting you to wherever they administer the test.

  3. #3 Mark Paris
    February 21, 2006

    The situation is not too different for enforcement of all traffic laws. The fact is, if you are cited for a traffic violation, as a matter of course you will not be given your Constitutional rights. I say this for a number of reasons, including the fact that you are presumed guilty and are penalized if you attempt to do anything other than admit guilt. Penalities are increased for pleading innocent. If a judge hears the case, you will be found guilty a very, very high percentage of times solely on the testimony of the police officer. Traffic enforcement is the only area that most citizens have any first-hand experience with the legal system, and it almost invariably works the opposite of way the legal system is supposed to work.

  4. #4 Mark Paris
    February 21, 2006

    I just thought about my own first-hand experience with drunk driving. I was on my motorcycle when a drunk turned left in front of me. I was not seriously injured, but someone called an ambulance and they took me and the drunk to the hospital. They put on lights and siren not for me, but because the drunk was essentially comatose from alcohol. His blood alcohol was way, way higher than the legal limit, based on an actual blood test in the ER, but the police thought it was too much trouble to cite him. They said if he had killed someone they would have cited him for DUI. I guess this is consistent with the way DUI laws are enforced: it is a police procedure, not a legal procedure.

  5. #5 deb
    February 21, 2006

    Good observations Mark Paris.

    We need to get drunks off the road, but I have always thought the best way to do that would be to test drivers as they entered the highway from an establishment serving drinks. Wouldn’t that send a more honest and direct message than some of the ‘game playing’ that goes on?

    Around my town, the blotter entries always begin ‘after being stopped for a possible vehicle defect ….’. We never hear how many were stopped that resulted in no citations.

  6. #6 David C. Brayton
    February 21, 2006

    All of my friends that are criminal defense attorneys say that you should demand a blood test, which is your right here in California.

    In California, it is illegal to drive under the influence and the law presumes that if the BAC is greater than .08, then a driver is under the influence. So, if you say to Officer Friendly, “I feel a bit of a buzz but I’ve only had one drink” then you’ve admitted to DUI regardless of your BAC.

    On the other hand, if you are a functioning alcoholic (i.e. someone who seems OK with a BAC of .20) then you are still under the influence.

    Functioning alcoholics are scary and weird. Some guy was arrested in my hometown after an accident. He started drinking wine at Eddie’s Bar at 8:00 in the morning and had 7 glasses of wine in less than 3 hours. His BAC was .24! He has been doing this for literally decades.

    Just amazing. If I have more than one glass of wine, I have a hangover the next morning. This guy has seven before lunch!

    I remember reading a Due Process case. The holding was something to the effect of ‘if we gave every driver the same amount of due process in traffic case as a murder case, the legal system would still be working on cases from the 1930s. So, the due process clause doesn’t require a huge amout of ‘process’ in traffic cases, especially given that if you didn’t speed this time around, you certainly broke the law many other times.

    This holding was the only practical result. We as a society simply can’t spend the same resources prosecuting drivers as we can prosecuting alleged rapists and murderers.

  7. #7 Martin Striz
    February 21, 2006

    I don’t have much sympathy for people in this situation. Yes, of course your driving performance is going to be affected by body size, metabolism, and tolerance, but we don’t have the time or resources to determine how people can handle alcohol on an individual basis. There has to be a template, cookie-cutter system, even if there is an error rate (and there will always be an error rate in any measurement). Your best chance of not getting screwed is to not drink and drive.

    If you make breathalyzer tests inadmissable in court, then you give lots of actual drunks the opportunity to get away.

  8. #8 Mark Paris
    February 21, 2006

    “…the only practical result..”

    I agree for the system the way it works now, but the way it works now is strongly skewed toward revenue generation rather than highway safety. That may or may not be the case for DUI, but it certainly is for most traffic enforcement. My local newspaper editor often talks about whether red-light cameras are a good idea based only on their revenue-generating potential. I hear no police or city official demur to that position. I have read that lengthening the duration of yellow lights more effectively reduces red-light running than cameras, but all that does is reduce accidents; it has no revenue generating effect. Oh well, my last traffic citation was decades ago. I speed where I think it’s safe and take my chances, just like everyone. And I never drive drunk.

    By the way, if you demand a blood test, are you charged for it?

  9. #9 coturnix
    February 21, 2006

    I never drink and drive. I only drink when I am stopped at the red light (OK, that is Coke I drink then….).

    For other traffic violations (parking, speeding), I always got off, but that meant I still had to pay large court costs…so yeah, it is all about revenue.

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