BAC refers to a person’s “blood alcohol content.” Under current Michigan law, the legal limit is .08 g/mL. This means that for every milliliter of blood coursing through a person’s veins, the legal limit says that this small amount of alcohol in the blood makes it illegal as a matter of law to operate a motor vehicle. The presence of this amount of alcohol makes the operation illegal, even if the person doesn’t feel the alcohol to slightest degree. Essentially, 99.92% of the blood shows no alcohol, but the person is drunk because the law says that the person is intoxicated.
Michigan Blood Alcohol Testing
99.92% of the blood shows no alcohol, but the person is "drunk" because the law says that the person is intoxicated
BAC is a historically new term. Measuring blood alcohol levels is a relatively new science dating back to the early 20th century. At various points during the 20th century, however, people began to look at the correlation between driving accidents and alcohol consumption. From 1939 to 1964, states began to pass laws prohibiting BAC amounts in excess of .015 g/mL. This was supported by the American Medical Association, which agreed that generally anyone over .15 would be intoxicated to the point where they were less than safe to drive.
Today, almost everyone will agree that a person is unsafe to drive at .15 BAC.
Unfortunately, a few pesky people insisted that they hadn’t drank enough to be a .15, and they argued to jurors that they weren’t drunk. Some of those jurors voted not guilty, and various interest groups viewed this as a bad thing.
From 1965 to 2003, states began to lower legal limits to .10 and .08 because too many presumably guilty people were being found not guilty by jurors. (Ah, ignore the whole presumption of innocence thing here... the advocates of these programs weren’t concerned about that whole “presumption of innocence” business, which they viewed as minor hindrance.) The logic was that it would be easier to convict people who were .15 if the law was lowered to .10 or .08.
In 2003, the logic of making it easier to convict people was brought to national attention when all states were required to lower their “per se” laws to .08. In other words, every state had to agree to lower the legal BAC to .08 or lose federal highway funds.
Today, various advocacy groups are petitioning the government to reduce the legal BAC to .05.
The question, of course, is whether this well-grounded in science. The answer is no.
Four out of five people show no signs of impairment at .08.
According to most studies, the effect of alcohol at .08 is moderate compared to .15. But maybe our social tolerance has changed, right? Well, a Washington State Police training manual warned officers when the legal limit dropped that officers had to be especially careful employing field sobriety tests because “only 20% of people exhibit signs of impairment at .08.”
In other words, 4 out of 5 people show no signs of impairment at .08, but the law will presume that they’re drunk and obviously going to cause accidents.
The problem dating back to the initial research is that every piece of data is based upon accident rates. While it’s true that drunk people increase their likelihood of causing or being involved in a fatal motor vehicle accident, the bulk of fatal accidents then and now involve neither nor alcohol. Distracted driving causes more accidents. Worse still, most accidents have no cause. They’re just accidents. Speeding along in an aluminum box at 70 mph is dangerous, after all.
Breath testing is currently performed in Michigan using a breath testing device known as the Datamaster.
Breath testing does not directly measure blood alcohol levels. Instead, the idea is that there is a correlation between the amount of alcohol in a person’s blood to the person’s deep lung air. Generally, for every molecule of alcohol that is detected in the expired breath during an exhalation, the blood will contain 2,100 times that amount of alcohol. (This makes sense if consider how oxygen and carbon-dioxide go in and out of the body while we breathe.)
Popular consensus says that the Breath-to-Blood ration is 2,100:1. Unfortunately, this is based upon averages and means, and the consensus isn’t very popular. Some people say that the average should be 2,000:1, while others say it should be 2,300:1.
And then we have to mention the statistical margins...
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Currently, BAC can be measured under Michigan law through blood, breath or urine testing. Urine testing is generally subject to so many errors that it is almost never employed by police. Moreover, police officers don’t like to collect urine samples for obvious reasons.
Breath testing is by far the most common test. Breath testing is cheap, fast, easy, and it does not involve bodily fluids. Breath testing is currently performed in Michigan using a breath testing device known as the Datamaster. Unfortunately, breath testing is not very accurate.