In order of most to least common, the 3 basic defenses to DWI in Texas would be:

  • Not Intoxicated
  • Not Driving
  • Not Driving While Intoxicated

I might be wrong about “Not Driving” being a more frequently viable defense than “Not While” but the third is still probably the least known to laypersons. The short version of the defense goes like this: Maybe there’s an accurate breath test over .08, but it’s barely over, and since the defendant’s BAC could have been rising between the time of the stop and the time of the Intoxilyzer results… reasonable doubt exists as to whether he was under .08 at the time of driving.

From an earlier post, DWI and the "While" Defense:


The point is that having a BAC of .085, for example, 30 to 45 minutes after the driving, does not in and of itself prove that the defendant was driving while intoxicated.


Depending on various factors, primarily the particular drinking pattern that night and the stomach contents, it is possible for the Defendant’s BAC to be higher at the time of the test, than it is at the time of driving. It is also affected by variations in human physiology as well.


This is most likely in scenarios where the defendant’s last drink was very near the time of driving; which – given what often happens at closing time – is not an unlikely scenario at all.


This isn’t just some crazy DWI defense lawyer theory here either – it’s both basic common sense, and basic science. So basic, that even the CMI manual for the Intoxilyzer 500 (used for breath tests here in Austin) admits that the defendant’s actual breath alcohol content at the time of the test may be “higher than, lower than or the same as” the BAC at time of driving.


So what’s the State to do when confronted with common sense and basic science telling them that “over .08” is sometimes “less than .08”? Change the rules, that’s what.


Proposed House Bill 170 attempts to ruin two of my favorite statutes (Code of Criminal Procedure 38.22 and 38.23) by following them up with a new section 38.24:


Article 38.24 Evidence of Alcohol Concentration


(a)    In this article, “offense relating to the operating of a motor vehicle while intoxicated” and “offense of operating a watercraft while intoxicated” have the meanings assigned by Section 49.09, Penal code.


(b)   For purposes of the prosecution of an offense relating to the operating of a motor vehicle or watercraft while intoxicated, it is presumed that the person had an alcohol concentration equal to or higher than 0.08 at the time of the offense if that level of alcohol concentration is shown by an analysis of the specimen of the person’s breath, blood, or urine taken from the person not later than 90 minutes after the time of the person’s arrest.


Retrograde extrapolation is the mathematical/scientific process by which an estimated BAC range for the time of driving is deduced/guessed by taking the BAC at the time of the test, the time since driving and other factors. These factors include when the suspect drank his last beer, .eg., to his last meal, and other considerations.


These are ultimately unknown factors no matter what the pre field sobriety test interview question and answers reveal from the defendant. And therefore, there’s room for some of that old reasonable doubt defense attorneys like to try and raise.


Since this is potentially a problem for the prosecution, they want to write into the law an unscientific instruction that allows them to argue that any test over .08 given within an hour and a half of driving automatically gives them a presumption of guilt. Since it’s unconstitutional to have an irrebuttable presumption in favor of the State in criminal cases, this proposed legislation can’t eliminate all tricks from the DWI lawyer’s bag, but it’s a start in the wrong direction.


After all, are they going to change the title of the offense to “Being Intoxicated After Driving”?


[Hat Tip: Houston DWI lawyer Mark "I like to call it DUI" Bennett]