Any practitioner that handles driving while impaired charges knows the significance of field-sobriety tests (“FSTs”) to the investigation and prosecution of drunk driving. Scientific research supports the basic idea behind the tests — that test performance on FSTs is an indicator of alcohol impairment. What about when the impairing substance isn’t alcohol at all? Do FSTs remain relevant for marijuana impairment? That was the question before the Massachusetts Supreme Court in Commonwealth v. Gerhardt, 81 N.E.3d 751, 2017 (September 19, 2017).
Marijuana is legal for all purposes in the Massachusetts for adults 21 and older, but driving while impaired on the substance of course remains a crime. Some states where marijuana is legal have enacted drug limits for purposes of establishing impaired driving. Washington, for instance, has settled on a per se limit of 5 nanograms of THC (the primary active ingredient in marijuana) per milliliter of whole blood for drugged driving cases, similar to the .08 blood alcohol content limit for alcohol. In Colorado, that same amount of THC in the blood creates a permissive inference of impairment. The District of Columbia, by contrast, has a zero tolerance policy: any amount of the substance in the body is sufficient to be charged with drugged driving. Massachusetts, like North Carolina, has no per se limit for drugged driving when it comes to marijuana; the government has to prove impairment. A chemical analysis, by itself, will generally not suffice to prove impairment without a per se statutory limit. In cases where there is no statutory limit for the permissible amount of the impairing substance in the blood (or where there is no chemical analysis at all), officers often use FSTs to try to prove impairment, as they would in alcohol impairment cases. FSTs are therefore frequently substantial evidence in many (if not most) impaired driving prosecutions, regardless of the type of impairing substance. Gerhardt is one of the first cases to take a hard look at the use of FSTs in the context of a marijuana-only impaired driving prosecution.
Gerhardt was charged with Operating Under the Influence (the equivalent of NC’s DWI offense) after being stopped for failure to burn rear headlights. The officer reported smelling recently burned marijuana, and Gerhardt admitted he had smoked around three hours earlier. Gerhardt performed the HGN test, the Walk and Turn test, and the One-Leg Stand test, and other non-standard tests. He had no cues of impairment during the HGN test or the non-standard FSTs, but the officer detected several cues on the Walk and Turn and One-Leg Stand. Marijuana and paraphernalia were found in the vehicle as well. The Commonwealth sought to introduce evidence of Gerhardt’s performance on the FSTs and the officer’s interpretation of them. Gerhardt challenged the admissibility of that evidence under the Daubert expert-testimony standards.
The court began by observing that standard FSTs were “designed to detect alcohol impairment” and that they do so by “assess[ing] an individual’s balance, coordination, dexterity, ability to follow directions, and ability to focus on multiple subjects at the same time.” Id. at 756. The court noted that established scientific research supports the reliability of the tests in the context of alcohol impairment, but that the same was not true for marijuana: “A significant amount of research has shown that consumption of marijuana can impair the ability to drive. There is ongoing disagreement among scientists, however, as to whether the FSTs are indicative of marijuana impairment.” Id. at 757. The court cites several studies that demonstrate the conflicting research—some studies have found substantial correlation between FSTs and marijuana impairment; some have found no such correlation; yet others find correlation between certain FSTs and marijuana impairment, but not others.
That said, the court wasn’t inclined to rule the tests completely irrelevant. Noting that the bar for relevance is low: “To the extent they are relevant to establish a driver’s balance, coordination, mental acuity, and other skills required to safely operate a motor vehicle, FSTs are admissible at trial as observations of the police officer . . .” Id. at 751. Just like the officer can attest to observations of driving, the odors of the vehicle or driver, and the appearance and behavior of the driver, the officer can testify to what he observed during the FSTs as a lay witness. “That marijuana can cause impairment of skills necessary to driving . . . is within the common experience and knowledge of jurors.” Id. at 759.
However, the court placed considerable limits on the use of such testimony, given the status of the science surrounding the use of FSTs in this context. The officer may not testify to whether the test was passed or failed and cannot testify that the results of the FSTs show marijuana impairment. Such testimony “improperly implies that the FST is a definitive test of marijuana use or impairment.” Id. at 759-760. Further, the officer should not call FSTs in a marijuana impairment case “tests”, as that signifies to the fact-finder that the FST is scientifically valid for the purpose of detecting marijuana impairment. The FSTs in this context should be referred to only as “roadside assessments.” Id. at 760. Perhaps most importantly, the lack of a scientific correlation between marijuana impairment and a defendant’s performance on FSTs means that the FST results, standing alone, are insufficient evidence to sustain a conviction. “The fact that FSTs cannot be treated as scientific ‘tests’ of impairment means that evidence of performance on FSTs, alone, is not sufficient to support a finding that a defendant’s ability to drive was impaired due to the consumption of marijuana, and the jury must be so instructed.” Id. (emphasis added). The court attached to its opinion a proposed jury instruction tracking that mandate. Finally, the officer also cannot offer a lay opinion that the driver was “high” on marijuana (although an expert opinion would be admissible). Because the effects of marijuana on individuals vary significantly, and because there is a lack of scientific evidence demonstrating common signs of marijuana impairment, a lay opinion that a defendant was intoxicated due to marijuana consumption is improper.
Impact in NC
So what’s the takeaway for practitioners? The case notes several studies on the connection between FSTs and marijuana impairment, which may be useful in a challenge to the use of FSTs in marijuana impairment cases. Because the studies are inconsistent, reference to them may support a finding that FSTs simply are not reliable in the context of marijuana impairment cases. Defense attorneys may point to Gerhardt as persuasive authority and argue for evidentiary limits on FST testimony in a marijuana impairment case similar to those imposed by the Gerhardt court, as well as for a similar jury instruction. Having the jury instructed on the fact that FSTs are not scientific evidence of impairment in this context would presumably be a powerful instruction. Likewise, preventing the officer from testifying that the defendant was impaired as a result of FST performance, that the defendant passed or failed the FSTs, that the officer’s lay opinion was that the person was impaired on marijuana, or from referencing the FSTs as “tests” at all, would be significant rulings in a DWI case with the potential to dramatically impact how the evidence of the case is presented to the finder of fact. When confronted with a marijuana-only impaired driving case, defense counsel is encouraged to consider filing a pretrial motion in limine addressing the expert testimony and relevance concerns of this evidence in the context of the case. The logic of Gerhardt may also support extending the same limitations to other impairing substances—where the scientific research does not conclusively link the defendant’s performance on FSTs to impairment on the substance at issue, there is a strong argument to be had that the testimony should be similarly limited.
Despite the ubiquitous nature of FSTs in impaired driving cases, their use in a non-alcohol impaired driving prosecution should not be accepted by the defense without a challenge seeking to properly contextualize their efficacy in this area. Further, even where the trial court allows the evidence over defense objection, many of the points that an attorney would raise in a voir dire hearing on the admissibility of FSTs would also go to the weight of that evidence before the jury. One can imagine a fruitful cross of the officer on many of the points raised in the opinion. We’ll have to wait and see how NC courts address these concerns. In the meantime, Gerhardt is an indication that FSTs are properly treated as having less probative value in a marijuana case than in the more-routine alcohol case, and that the defendant is entitled to certain protections limiting the way that evidence is presented, at least as long as the science remains uncertain.