Archive for April, 2008

Law Trumps Scientific Truth in DUI Cases

Saturday, April 5th, 2008

It is an unfortunate fact that law and politics repeatedly trump science when it comes to prosecuting citizens accused of drunk driving…..  

In People v. Bransford, to cite one notable example, the California Supreme Court was confronted with a defendant who was challenging his DUI conviction on the grounds that he was not permitted to offer scientific evidence to the jury. Specifically, he was not permitted to offer the testimony of recognized experts that the breath machine’s computer was programmed to assume that there were 2100 parts of alcohol in his blood for every 1 part it measured in his breath.

He was also prevented by the trial judge from offering further evidence that this 2100:1 ratio was only an average — and that the actual ratio varied widely from person to person, and within one person from moment to moment. If, for example, a suspect’s ratio had been 1300:1 at the time he blew a .10% on the machine, his true blood-alcohol would have actually been .06% — that is, he would have been innocent.

The Supreme Court of California affirmed the conviction, however, ruling that such scientific facts are irrelevant: the law was written in a way that concerned the amount of alcohol in the blood ”as measured on the breath”. In a display of either twisted logic or ignorance of the scientific facts involved, the Court simply said that the crime consisted of the amount of alcohol in the blood — but only as measured on the breath. In other words, although the crime is having .08% alcohol in the blood, you can’t offer evidence about the amount of alcohol actually in the blood!

An amazing decision. More interesting, perhaps, is the language in the opinion — an opinion which gives us a window into the justices’ minds. In what must have been a complete failure to appreciate the significance of what they were writing, the Court justified its ruling in a rather frank — and incredible — admission of its hidden agenda:


It will increase the likelihood of convicting such a driver, because the prosecution need not prove actual impairment…Adjudication of such criminal charges will also require fewer legal resources, because fewer legal issues will arise. And individuals prosecuted under such a statute will be less likely to contest the charges.  People v. Bransford, 8 Cal.4th 894 (1994).


In other words, preventing an accused from defending himself with scientific truth serves justice by making it easier to get convictions!

Are all judges oblivious to the truth? Not entirely. One judge, Justice Joyce Kennard, dissented from the majority opinion. Recognizing the truth, she wrote in a separate opinion:


The majority…has on its own created the new crime of driving with alcohol in one’s breath.

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How to Overcome Scientific Facts: Pass a Law

Wednesday, April 2nd, 2008

The drunk driving laws make it a criminal offense to drive a vehicle while under the influence of alcohol (DUI) or while having a blood-alcohol concentration (BAC) of .08% or higher. It is not, however, a criminal offense to be under the influence or to have a BAC of .08% while taking a breath or blood test in a police station an hour or two after driving.

So how does the prosecution prove what the BAC was when the defendant was driving?

It’s a problem. You can try to guess what the BAC was in a DUI case by projecting backwards, using average alcohol absorption and elimination rates, but it’s only a very inaccurate guess. The process is called retrograde extrapolation — a fancy name for trying to guess backwards.

The problem is that everyone has a different metabolism, and even a given person will metabolize alcohol at different rates depending on many variables. In one study, for example, researchers found a wide range of matabolism rates: some individuals can absorb alcohol and reach peak blood-alcohol levels ten times faster than others. Dubowski, “Absorption, Distribution and Elimination of Alcohol: Highway Safety Aspects”, Journal on Studies of Alcohol (July 1985).

As a result, scientists have concluded that the practice of estimating earlier BAC levels in DUI cases is highly inaccurate and should be discouraged. From the recognized expert in the field, Professor Kurt Dubowski of the University of Oklahoma:


It is unusual for enough reliable information to be available in a given case to permit a meaningful and fair value to be obtained by retrograde extrapolation. If attempted, it must be based on assumptions of uncertain validity, or the answer must be given in terms of a range of possible values so wide that it is rarely of any use. If retrograde extrapolation of a blood concentration is based on a breath analysis the difficulty is compounded.  21(1) Journal of Forensic Sciences 9 (Jan. 1976).


So, Mr. Prosecutor, you’ve got a breathalyzer reading of .10% an hour or two after the driving and the scientists say you can’t accurately project that BAC back to the time of driving: if alcohol was still being absorbed and the BAC was rising, for example, it could have been a .07% or lower. That kind of leaves you in a pickle. What do you do?

Simple: You just get the legislature to pass a law saying that the blood-alcohol when tested is the same as it was when driving.

What? But that’s not true: It’s a scientific fact that BAC constantly changes as alcohol is metabolized. How can we legally presume what we know is not true?

Well, yes, but we can never really know, can we? And it sure makes the prosecutor’s job easier, doesn’t it? Let the defendant try to prove what his BAC was an hour or two earlier.

That’s right: Most states now have laws saying your BAC was the same 3 hours earlier — unless you can prove it wasn’t! Typical is California’s law:


It is a rebuttable presumption that the person had 0.08% or more, by weight, of alcohol in his or her blood at the time of driving the vehicle if the person had 0.08 percent, by weight, of alcohol in his or her blood at the time of performance of a chemical test within three hours after the driving.  Vehicle Code sec. 23152(b).

Wait a minute….What about the truth?  And what about the State having the “burden of proof” — proof beyond a reasonable doubt? How can the law simply presume guilt and force the defendant to disprove it? What about the “presumption of innocence”?

Details, details. The important thing here is that we get these drunk drivers off the road, right?

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