Not Guilty Defenses to Impairment and the Alcohol Concentration Number
Under North Carolina driving while impaired (“DWI”) law, “a person commits the offense of impaired driving if he drives any vehicle upon any highway, any street, or any public vehicular area within this state: (1) While under the influence of any impairing substance; or (2) After having consumed sufficient alcohol that he has, at any relevant time after driving, an alcohol concentration of .08 or more. The results of a chemical analysis shall be deemed sufficient evidence to prove a person’s alcohol concentration.” (NCGS 20-138.1). That’s a lot to unpack. Here, we’ll focus on the two prongs of the statute that the district attorney will use to prove the intoxication part of the case.
While Subject to an Impairing Substance
The first way the state can prosecute a DWI charge is by proving beyond a reasonable doubt that the person was driving while subject to an impairing substance. This manner of prosecution applies to all impairing substances. It could be alcohol, illegal drugs such as heroin or cocaine, or even a legal drug lawfully prescribed by a doctor. In fact, it could be a combination of two or more of these.
So, what does it mean to be “subject to an impairing substance?” In a nutshell, it means noticeably impaired. This is an inherently subjective analysis. Law enforcement officers are supposed to be trained in issuing standardized field sobriety tests as part of their DWI investigation, but often those tests are more helpful to establish probable cause to arrest than proof beyond a reasonable doubt of guilt. Some people just don’t do well on these physical tests. Noticeably impaired might be hard to find beyond a reasonable doubt unless there is gross impairment, such as someone so drunk they are having trouble standing up. When there is not gross impairment, the prosecution usually falls back on the alcohol concentration analysis to find someone guilty of DWI charges.
An Alcohol Concentration of .08 or More
This second prong, clearly, applies to alcohol only. An alcohol concentration can be reported by breath test results or blood test results. Let’s refer to both breath alcohol concentration and blood alcohol concentration as one and the same with “BAC.” For this discussion, the timing of the tests is more important than the methodology of the tests.
The roadside breath test administered before arrest is known as a preliminary breath test (“PBT”) and is not admissible in court. Thus, we do not consider the PBT here. The BAC that will be used against a defendant is the result from the second breath test that is performed at the jail after arrest. This breath test is typically administered about an hour after the person was arrested, and even longer after the person was driving. A blood test can take even longer to administer than a breath test, putting the driving even farther back in the rearview mirror. Why is this important? Because the tests are analyzing your BAC at the time the tests were administered, not at the time you were driving. The tests cannot say what your alcohol concentration was at the time you were driving, just what it was an hour after driving, or more!
BAC .08 or Above is not Proof Beyond a Reasonable Doubt of Guilt
This is where the “at any relevant time after driving” analysis of the statute comes into play. To be found guilty of DWI under this prong of the statute, you must have a BAC of .08 or above at the time of the driving, not an hour or more after the driving. A BAC of .08 or more, by law, is presumptive of guilt, but it is not conclusive. The BAC is nothing more than circumstantial evidence of what your BAC would have been at the time of the driving. A person’s alcohol concentration is never static. It is either going up or coming down. Some factors affecting the direction the BAC is travelling include when the last drink was consumed, how much food was on the person’s stomach, and physiological characteristics such as the person’s weight, body mass index, fitness, and biology. The rate of absorption or the rate of metabolization varies based on these types of factors as well. Did the law enforcement officer take time to investigate all these factors? No! They just have a naked BAC number. The prosecution wants to make an inference that the BAC would be lower an hour later than it was at the time of driving, but why? It is often more plausible that a person’s alcohol concentration is on its way up, not on its way down. The argument for a not guilty verdict is strengthened when there is lack of evidence of impairment.
Fallibility of the Testing Procedures
Breath or blood analysis of alcohol concentration is not an exact measurement. It is based on algorithms and assumptions applied to a chemical analysis of the breath or blood sample. It is not a perfect analysis, and some even go as far as to call it junk science. There is inherent fallibility to these tests. What does that mean? There is a built-in margin of error. The BAC reading is the sweet spot in the middle of that margin of error. It is not uncommon to see breath or blood tests where the analysis’ margin of error already falls below a .08 BAC.
Driving Under the Influence of Heroin
For the sake of completeness, there is a third prong to North Carolina’s DWI law that is not as commonly charged. It is illegal to drive while having any amount of a schedule I controlled substance in your system, which is most commonly heroin. This is the one drug classification where there is a numerical value like there is for alcohol, and the schedule I number criminalizes anything above 0.0.
Written by Landon White.
