How to Overcome Scientific Facts: Pass a Law

Posted by Lawrence Taylor on 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?

Share
  • jim

    ANOTHEWR point HERE IS, And its a small point, but, ,….

    you can not just say by weight in blood, thats half the equation,

    it should be descibed by w/w. w/v, or v/v.

    weight per weight, weight pewr volume. or volume per volume.

    unless tha acutauuly take a sample of a persons blood and detertmine the specific gravity of it, the value, by all scientific rights, can not be valid.

    wheather you are reporting thec reesults in weight/weight, or weight per volume, you must have either the volume of blood in a persons body, or the sopecofic gravity of that blood, either or.

    there needs although to be a line drawn in the sand somewhere.

    but please, dont just sat by weight, please indicate weight per weight, or weight per volums, please do not for a minute say to me thar the specific gravity of blood is equal to the specific fravivity of alcohol….

    in fact the specific gravity of alcohol is about 0,875, whiled blood is more about 1.0, thats around a 12 percent difference, and wuld actually be significant in this typoe of calculation for the determination of blood alcopho concentration, BAC

  • jim

    TO BRING MY LAST POST UP FURTHER, IT IS NOT THE DEFENDANTS THAT SPLITRING HAIRS HERE BETWEEN O.N79. 0M80, AND 0.085, IS IT THE STATE, THE LEGISLATURE.

    THEREFORE THE LEGISLATURE, MUST DEFINE THE UNITS .

    BUT IN NJ AT LEAST THEY DO NOT, THEWY JUST SAY BY WEIGHT.

    THAT IS A SCIENTIFIC WRONG.
    BAC MUST BE DIFINED AS W/W/ W/V. OR V/V

    IT SOUNDS LIKE IN CAILIFORNIA THEY ARE MJAKING THE SAME MISTAKE.

    NOW, HIGH COURTS WILL SAY THE 2100-1 RATIO IS A ESTIMATE AND TAKES INTO ACCOUYNT EROOR ON BOTH SIDES, BUT, THEN DEFENDANTS SHGOULD HAV E THE RIGHT TO ARGUE THAT ERROR, AND NOT B E CONVICTED OF A
    “PER SE” VIOLATION, WHEN I FACT THE UNITS ARE NOT EVEN PROPERLY DESCRIBED

  • jim

    AND I AM TALKING ABOUT ALL EFENDANTS, NOT JUST THE ONES WHIO HAVE AN ATTORNEY WILLING TO MAKE AN ARGUMENT, AND THUS, FOR BORDER LINE CASES GET A PLEA AGREEMENT….

    I AM SAYING THAT IT IS THE RIGHT OF ALL DEFENDANTS TO HAVE A STATE LEGISLATURE SAY IN THE STATUTE THAT IT IS 0.08% BAC W/W OR W/V- PICK ONE ANSD STCK WITH IT.

    I AM BESIDE MYSELF IN THIS IDIOCY WITH DUI LEGISLATION

  • jim

    LETS SAT, FOR ARGUMENT SAKE, A PERSONS REPORTE POLICE REPORT BAC IS 0.08.

    BUT IF THAT BAC IS REPORTERD IN FAC T, AS WEIGHT PER WEIGHT, BUT THE SPECIFIC GRAVITY OF A PERSONS BLOOD IS LESS THE 1.00. THEN THE ACTUALY BAC MAY BE 0.079, THUS MAKING IT LEGAL HE/SHE DROVE.

    THE FAC T IS IF THE STATE WANTS TO SPLIT HAIRS HERE, THERE MUST BE EQUAL PROTECTION UNDER THE LAW, AND THE SPEC IFIC GRAVITY OF EACH DEFENDANTS BLOOD MUST BE TAKEN INTO ACCOUNT

  • LabMonkey

    In states where they have passed a time limit on the perse laws (in an attempt to STOP retrograde extrapolation) the prosecutors themselves are now ASKING for retrogrades.

    Case example:

    Someone is stopped for DUI, the law says if their BAC/BrAC is over 0.08 within 2 hours of driving they are guilty. Well in cases where the test is outside of the two hour window, the prosecutors routinely ask police chemists to retrograde back to time of stop + 1 hour 59 minutes.

    I’ve even heard of cases where a test taken at nearly two hours after the stop came back just under 0.08, so the prosecutor wanted a short retrograde inside the two hour window that would out the reading above the 0.08 magic number.

    They had a law passed to make retrograding ineffective for the defense, stating it was because such a process had “too many variables and wasn’t reliable”. Once the law was passed, they start using retrogrades for their own benefit.