Per se impairment, reasonable doubt, margins of error, and all that lies between

G.S. 20-138.1(a)(2) prohibits a person from driving a vehicle upon a highway, street or public vehicular area after having consumed sufficient alcohol that the person has, at any relevant time after the driving, an alcohol concentration of 0.08 or more. S.L. 2006-253 amended this subsection to provide, effective for offenses committed on or after December 1, 2006, that “[t]he results of a chemical analysis shall be deemed sufficient evidence to prove a person’s alcohol concentration.” The meaning and constitutionality of this latter provision were considered and upheld by the court of appeals in State v. Narron, 193 N.C. App. 76 (2008) (discussed in this post). Narron held that the “shall be deemed” provision, contrary to the defendant’s argument, did not establish a mandatory presumption.  Instead, it merely set forth the prima facie standard for proof of impairment under the per se prong of G.S. 20-138.1. The court explained that the “[r]esults of a chemical analysis are sufficient evidence to submit the issue of a defendant’s alcohol concentration to the fact-finder” who “may find it adequate proof.” Id. at 81, 84.

Let’s suppose you are a defense lawyer (a proposition that is hardly a stretch for many readers) representing a defendant charged with impaired driving based on a reported alcohol concentration of 0.08 resulting from a breath test administered in compliance with all statutory and regulatory procedures. On what basis might you argue to the judge in district court or the jury in superior court that the alcohol concentration result introduced into evidence by the State fails to prove the defendant’s alcohol concentration beyond a reasonable doubt?

One argument made with some frequency is that the defendant showed no outward signs of impairment. She drove well and satisfactorily performed field sobriety tests. This, the defense attorney argues, casts doubt on the veracity of the alcohol concentration results reported from the chemical analysis.  There’s nothing at all improper about this argument framed in this way. Determining whether the evidence establishes the defendant’s guilt beyond a reasonable doubt unquestionably is the province of the finder of fact. See, e.g., State v. Finch, 244 P.3d 673, 679 (Kan. 2011) (stating that proof of the elements of a per se criminal statute will not compel conviction as a matter of law as “[t]he defense may still attack the State’s proof and attempt to discredit its witnesses, their machines, and their methods during the State’s case-in-chief or later” and “[t]he jury may finally agree that reasonable doubt prevents a conviction.”) Moreover, “[t]he State’s introduction of evidence supporting the statutory elements in a per se criminal statute does not endow the evidence with infallibility.” Id.

There’s a variant on this argument, however, that is not supported in law. Defendants sometimes argue that the State’s evidence is insufficient as a matter of law to establish impaired driving under the per se prong unless, in addition to proving the defendant’s alcohol concentration, the State also proves that the defendant was appreciably impaired. This argument may be hold-over from the statutory scheme that preceded the Safe Roads Act of 1983, which defined a per se violation of the impaired driving laws as a lesser included offense of driving under the influence and under which the results of a chemical test yielding a result of 0.10 or more created a presumption that the person was under the influence. See G.S. 20-138 (Cum. Supp. 1981); G.S. 20-139.1 (Cum. Supp. 1981); State v. Shuping, 312 N.C. 421 (1984). Whatever its origins, this argument reflects a misunderstanding of the impairment element of impaired driving as a single element that may proved in any one of three ways. See State v. Coker, 312 N.C. 432, 440 (1984); Narron, 193 N.C. App. at 79. As the court of appeals clarified last month in State v. Arrington, __ N.C. App. __ (August 16, 2011), “it is not necessary for the State to prove that the defendant was appreciably impaired, uncooperative, or driving in an unsafe manner in order to prove that defendant is guilty of a violation of N.C. Gen Stat. § 20-138.1(a2). To prove guilt, the State need only show that defendant had an alcohol concentration of 0.08 or more . . . .”

Another argument relied upon by defendants is that the “margin of error “ for the breath testing instrument renders the State’s proof of per se impairment based on a breath alcohol concentration of .08 unreliable. The argument generally points to one of two sources for the margin of error. First, administrative regulations deem a breath-testing instrument to be accurate if the control sample used to verify instrument accuracy before the defendant’s test measures at the expected result of 0.08 or 0.01 or less than the expected result.  See 10A NCAC 41B .0101. Second, G.S. 20-139.1(b3) deems admissible results of a chemical analysis consisting of “two consecutively collected breath samples [that] do not differ from each other by an alcohol concentration greater than 0.02,” and provides that “[o]nly the lower of the two . . . can be used to prove a particular alcohol concentration.” G.S. 20-139.1(b3). Under the first basis, the margin of error is 0.01 (though, ironically, any such variance engenders a lower alcohol concentration result than actually is present); under the second, the margin of error is 0.02. While alleged unreliability based upon a margin of error, like other questions about the reliability of a reported alcohol concentration result, is fair game for the fact-finder’s consideration, see, e.g., Finch, 244 P.3d at 679, an alleged margin of error does not render the State’s evidence of impairment insufficient as a matter of law. See Shuping, 312 N.C. 421 (1984) (rejecting defendant’s challenge to the sufficiency of the evidence based on an alleged margin of error and characterizing the 0.01 deviation allowance below the expected reading as “a safeguard to ensure that when the actual test is subsequently run, any possible error during actual testing is in favor of defendant”); Arrington, __N.C. App. at __ (rejecting defendant’s contention that since his reported alcohol concentration of 0.08, the result from both breath tests, was the lowest for which he could be convicted of a per se violation, the “‘margin of error’ of the [instrument] should be taken into account to undermine the State’s case against him”; determining that the testing satisfied statutory requirements, was reliable, and accurately identified the defendant’s level of impairment.)

If there are other common bases on which alcohol concentrations from chemical analysis are alleged to be unreliable, or other relevant grounds on which proof of per se impairment is alleged to be lacking, please send in a comment to let me know.