1. Loss of the normal use of one's mental faculties due to the introduction of
alcohol, a drug, a controlled substance, or a combination thereof, into the
2. Loss of the normal use of one's physical faculties due to the introduction of alcohol, a drug, a controlled substance, or a combination thereof, into the body; or
3. Having an alcohol concentration of .08 or higher.
There are two training manuals that are a must have for any lawyer who practices DWI defense in Texas - DWI Detection and Standardized Field Sobriety Testing (published by NHTSA) and the Texas Breath Alcohol Testing Program Operator Manual (published by the Texas Department of Public Safety).
Both of these manuals may be used to impeach the state's witnesses on the subject of "loss of normal use." A criminal defense attorney who knows what he's doing can cross-examine the state's witnesses with these manuals through the "learned treatise" exception to the hearsay rule.
According to the breath test manual, "[i]t is not the alcohol in the peripheral areas of the body which impairs a person's coordination, but the alcohol concentration in the CNS (central nervous system) tissue." This seems to indicate that it's not the concentration of alcohol in a person's breath that is critical -- it's the concentration of alcohol in a person's central nervous system (brain, brain stem and spinal cord) that is critical.
The breath test manual goes on to state that "[t]he first effect of alcohol is the impairment of judgment." That's because "[a]lcohol affects the brain in reverse order of how the brain develops." In other words, the higher level brain functions, such as judgment, logic and reason are affected before the lower level brain functions, such as breathing and digestion. According to the breath test manual, "[p]sychomotor skills are motor actions (physical faculties) proceeding directly from mental activity."
The NHTSA manual states that alcohol "doesn't affect a person until it gets into their central nervous system, i.e. the brain, brain stem and spinal cord."
This is important because the manuals the state uses to train its experts tell us that alcohol affects one's mental faculties before it affect's one's physical faculties. Thus, evidence indicating the citizen accused had the use of his mental faculties at the time of driving can be used to refute the state's argument that if a person performs poorly on the police coordination exercises, he must be intoxicated.
Now when you ask the arresting officer or the state's breath test expert whether alcohol affects one's mental or physical faculties first, and he tells the jury alcohol affects them both equally, you can pull out your manuals and read the training material that contradicts his "expert" testimony. But in order to do that, you have to know what's in those manuals.
If you're defending citizens accused of DWI, and you don't want to commit malpractice, you need to get those manuals ASAP.