In about one out of five cases, the DWI defendant refuses to provide a chemical sample of breath or blood. As a result, the prosecutor must rely on circumstantial evidence of intoxication, and as we all probably know, such evidence is always subject to interpretation.
Circumstantial evidence cases are also harder for prosecutors to win because they cannot use the DWI law’s per se section, which states that drivers who have a BAC above the legal limit (.08 in most cases) are guilty of DWI as a matter of law.
In nearly all cases, this evidence comes from the field sobriety tests, and the ones performed at the scene are usually the ones which most closely indicate the defendant’s level of intoxication, if any, while operating the motor vehicle.
What Are the Approved FSTs?
First of all, there are a number of field sobriety tests that have little or no scientific basis, such as the reciting-the-ABCs test or the finger-to-nose test. A good DWI defense lawyer can usually have these results excluded altogether, or at least minimize their effect on the jury.
The three National Highway Traffic Safety Administration approved tests, and therefore the ones that matter most in terms of the case, are as follows:
- One Leg Stand: In the OLS, the subject must hold one leg up for a certain number of seconds without losing balance. Prosecutors often point out ticky-tack technical flaws, such as holding the leg at the wrong angle or putting it down a fraction of a second too early, in an attempt to convince the jury that the defendant “failed” the test.
- Horizontal Gaze Nystagmus: If conducted by a highly-trained test administrator under controlled conditions, the HGN test, which measures involuntary eye movements, is about 80 percent accurate in terms of predicting intoxication. But the situation at the scene, which normally includes flashing lights and whizzing cars, mean that the conditions are anything but controlled.
- Walk and Turn: The WAT is also known as the heel-to-toe walk. Many subjects must walk an imaginary line over an uneven surface in the dark, a feat that’s almost impossible to accomplish.
As always, the jury has the final say on whether the defendant “passed” or “failed” the tests, and therefore the question of whether the defendant was intoxicated while operating a motor vehicle.
Connect with an Experienced Attorney
Circumstantial evidence DWI cases are inherently weaker than cases which involve a breath or blood test. For a free consultation with an experienced DWI defense lawyer in Houston, contact the Law Office of Jim Medley.