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Drunk driving

Drunk driving is the act of operating a motor vehicle whilst under the debilitating effects of alcohol. It is illegal in most (all?) jurisdictions; laws prohibiting it refer, for instance, to driving while intoxicated (DWI) or drunk in charge (of a vehicle). Such laws tend to define a particular level of alcohol in the blood as the threshold of drunkenness. The most common blood alcohol concentration (BAC) in the United States is 0.1 for the legal limit of intoxication. Other states have taken much stricter measures by making 0.08 the legal limit of intoxication.

History of drunk driving laws

The first jurisdiction in the United States of America to adopt laws against drunk driving was New York in 1910, with California and others following. Early laws simply prohibited driving while intoxicated, with no specific definition of what level of inebriation qualified.

(When were first DUI laws enacted in other jurisdictions / nations?)

Critique of blood alcohol readings

This section is the previous content of this page. It needs wikifying and NPOVing.

One of the greatest sources of error in blood-alcohol testing is the consistently recurring fallacy that the individual tested is perfectly average in certain critical physiological traits. Put another way, obtaining an accurate blood-alcohol reading is completely dependent on the validity of a number of scientific assumptions. Unfortunately for the person being tested, these assumptions are usually incorrect: The person tested is rarely "average" in even one of these critical characteristics, let alone in all of them.

Counsel in a DUI case will constantly be confronted by these almost hidden assumptions. And it is very important that these false premises be brought out for the jury--along with the fact that the final readings fall with the presumptions.

Thus, for example, all breath testing devices depend on the assumption that the ratio between alcohol in the exhaled breath and alcohol in the blood is 1 to 2100. In fact, the machine is designed to produce a reading based on that assumption; the accuracy of the reading is directly tied to the accuracy of the presumption. Yet, the actual ratio in any given individual can vary from 1:1300 to 1:3000, or even more widely. Thus a person with a true blood-alcohol level of .08 but a breath-to-blood ratio of 1:1700 would have a .10 reading on an "accurate" breath testing instrument.

Put simply, these machines do not test individuals. Rather, they test the average person over and over again, but using the subject's breath.

Yet another example of the assumption of "averageness" can be found in urinalysis. When a subject's urine is analyzed for blood-alcohol, a presumption exists that there are 1.3 parts of alcohol in the bladder's urine for every 1 part of alcohol in the blood. This 1:1.3 ratio is as fallacious as the 1:2100 ratio--that is, it is based entirely on the ratio found in the average person. As is discussed more fully in 8.4.1 however, the actual ratio found in any given individual can vary greatly. And as the ratio is in error, so will be the final blood-alcohol reading.

Another example of this constant reliance on averages shows itself when the prosecutor offers evidence of retrograde extrapolation. The blood-alcohol level at the time of testing is not relevant to the charge, of course, and so the state will offer evidence to show what the level was when the defendant was driving. This is commonly done by extrapolating backward--that is, computing the earlier blood-alcohol level by estimating how much alcohol had been eliminated or "burned off" in the interim between driving and testing. But this requires two assumptions: The blood-alcohol level was declining, and the rate of elimination is known. This second assumption involves the further assumption that the "burn-off" rate was .015 percent per hour. How does the prosecution know that the defendant was eliminating (assuming he was eliminating) at that rate, and not at .005 percent or .3 percent! Quite simply, the prosecution does not know: It merely assumes that the defendant eliminates at the average rate. And, of course, error in such an assumption translates into error in the extrapolation.

This ubiquitous "average person" in the DUI arena is not limited to chemical analysis. We even find him with the arresting officer in the field. When the officer administers the increasingly common "horizontal gaze nystagmus test as part of the battery of field sobriety tests, he operates on the assumption that the suspect is "Mr. Average." The officer has been trained to "read" at what angle the suspect's eyes begin jerking. A blood-alcohol reading can theoretically be obtained by subtracting the angle from 50; jerking at 35 degrees, for example, would mean the suspect has a blood-alcohol level of .15 percent. Where does the magic figure of 50 come from? The average person.

An alternative method of administering the nystagmus test is to "flunk" the person if jerking begins before 40 or 45 degrees. Why? Again, because the average person would theoretically have .10 or .05 percent alcohol in his blood at this point. In either test, of course, we do not know what the individual's actual "baseline" is--that is, the angle at which his eyes would begin jerking if he were sober. In both cases, the individual is assumed to be physiologically identical to the theoretical "average" person.

Don Nichols, one of the foremost DUI lawyers in the country today, points out to juries, in appropriate cases, that his client is female, Chinese, and deceased--despite obvious evidence to the contrary. He then explains that statistically there are more women than men in the world, more Chinese than any other nationality, and more dead human beings than living ones. Statistically, then, the average person is female, Chinese, and deceased--and so, according to the prosecution, must be his client. He usually also asks the jury how many of them have 2.3 children--the average in the United States.

Counsel must make clear to the jury in the course of the trial that the prosecution is making multiple erroneous assumptions about the defendant, and that these assumptions are critical to the validity of the blood-alcohol reading. As the computer technicians are fond of saying, "Garbage in--garbage out."

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