Friday, January 16, 2009

Blowing while intoxicated

According to the Texas DWI statute, a citizen must be intoxicated at the time of driving in order to be convicted of driving while intoxicated.  In cases in which the citizen accused blew into the state's breath machine, the state has a powerful piece of evidence that juries love to rely upon. That is, if the state can prove that the citizen's alcohol concentration was .08 or greater at the time of driving.

In order to do this, the state's expert "back-extrapolates" the breath test result to estimate the alcohol concentration at the time of driving.  In order to perform this "back-extrapolation," the state's expert takes the alcohol concentration at the time of the test and then, using the Widmark equation, calculates what that alcohol concentration would have been at the time of driving.

The state's expert will even estimate the number of alcoholic drinks the citizen consumed to get to this extrapolated alcohol concentration.  Of course it's all a giant guessing game as the state's expert doesn't know how much the citizen had to drink, what the citizen had to drink, over what span of time the citizen drank it, what the citizen had to eat, when the citizen ate, etc.  This generalization can cause some headaches for the state, as evidenced in the Mata decision where the Court held that without concrete facts regarding the weight and sex of the citizen and some specifics as to food and drink, this "back-extrapolation" was inadmissible.  And if that number is inadmissible then the breath test becomes just another piece of evidence for the jury to sift through in its deliberations.

But now the legislature is coming to the rescue.  House Bill 170, introduced by Jimmie Don Aycock of Lampasas, would change the DWI statute to create a presumption that a breath test result within 90 minutes of driving would be accurate as to the time of driving.  In other words, the state would no longer have to "back-extrapolate" a breath test result in order to show its relevance.  It would also invalidate the presumption of innocence in drunk driving cases.

In Representative Aycock's world, a citizen would be guilty of driving while intoxicated if the state can prove the citizen was intoxicated up to 90 minutes after driving.  Now there's no need to worry about pesky little details like proving the elements of a crime beyond a reasonable doubt.

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