Ct.App. 4/2 E041226 San Bernardino County Super. Ct. No. TRE038083 Judge: Michael A. Smith
The opinion of the court was delivered by: Corrigan, J.
A defendant accused of driving under the influence of alcohol can be charged under two separate code sections. The "generic DUI" provision prohibits driving "under the influence" of alcohol. (Veh. Code, § 23152, subd. (a) (hereafter § 23152(a).)*fn1 The "per se DUI" provision prohibits driving with a blood-alcohol level of 0.08 percent or more. (§ 23152, subd. (b) (hereafter § 23152(b).) This case concerns how a generic DUI charge can be proven, or defended, at trial.
The Vehicle Code requires all drivers who are lawfully arrested for DUI to submit to chemical testing of the blood or breath to determine the alcohol content of their blood. (§ 23612, subd. (a)(1)(A).)*fn2 Whereas a blood test directly measures the subject‟s blood-alcohol level, a breath sample must be converted to derive a blood-alcohol percentage. The conversion factor, known as a "partition ratio," reflects the relationship between alcohol measured in a person‟s breath and alcohol in the blood. Breath-testing machines in California incorporate a partition ratio of 2,100 to 1, which means the amount of alcohol in 2,100 milliliters of breath is considered equivalent to the amount of alcohol in 1 milliliter of blood. It is undisputed, however, that partition ratios can vary widely, both in the general population and within an individual.
Defendant was charged with generic and per se DUI after he produced a breath sample indicating a blood-alcohol concentration of 0.10 percent. By statute, if a chemical test within three hours of driving measures a driver‟s blood alcohol at 0.08 percent or more, the driver is presumed to have been driving "under the influence" of alcohol. (§ 23610, subd. (a)(3) (hereafter § 23610(a)(3).) Defendant claims he was wrongly prevented from introducing evidence about partition ratio variability to rebut this presumption. In People v. Bransford (1994) 8 Cal.4th 885, 887-888 (Bransford), we confronted a similar claim in the context of the per se DUI offense. We concluded evidence about partition ratio variability is irrelevant in those cases because the Legislature incorporated a 2,100-to-1 partition ratio within its definition of the offense. (Id. at pp. 892-893.)
However, a generic DUI charge is defined differently, and the presumption is not part of that definition. A generic DUI charge requires proof that the defendant‟s ability to drive safely was impaired because he had consumed alcohol. We conclude this difference is significant and hold that competent evidence about partition ratio variability may be admitted to defend against a generic DUI charge. Reversal is not required, though, because any error in this case was harmless under People v. Watson (1956) 46 Cal.2d 818, 836.
Defendant was stopped after an officer saw him drive through two red lights. Defendant‟s eyes were watery and bloodshot, his speech was slurred, he smelled of alcohol, and he admitted he had consumed a beer. Defendant was arrested and given a breath test about an hour after the initial stop. Defendant blew into the machine five times but produced only two samples sufficient for testing.*fn3 Both valid samples registered a blood-alcohol level of 0.10 percent.
Defendant was charged with both generic and per se DUI.*fn4 At trial, a prosecution expert testified that a person is too impaired to operate a motor vehicle safely if he displays slurred speech and bloodshot, watery eyes, commits traffic infractions, performs poorly on field sobriety tests, and records a blood-alcohol level of 0.10 percent in a breath test. A defense expert agreed that scientific authorities consider a person with a blood-alcohol level over 0.08 percent to be under the influence of alcohol. However, he considered defendant‟s test results unreliable because the machine‟s repeated failure to register sufficient samples suggested it was not functioning properly. The defense expert also testified that breath-testing machines have a margin of error of 0.02 percent.
After both sides had rested but before closing arguments, defense counsel moved to reopen to present expert testimony about partition ratio variability in connection with the generic DUI charge. The record does not disclose whether defendant intended to introduce evidence of his own partition ratio or evidence about the variability of partition ratios in the general population. The court denied the motion and instructed the jury regarding the statutory presumption of intoxication. (CALJIC No. 12.61.) Specifically, with regard to the generic DUI count, the jury was instructed: "If the evidence establishes beyond a reasonable doubt that at the time of the chemical analysis of the defendant‟s blood, breath or urine there was .08 percent or more, by weight, of alcohol in the defendant‟s blood, you may, but are not required [to,] infer that the defendant was under the influence of an alcoholic beverage at the time of the alleged offense."
The jury convicted on the generic DUI charge but hung on the per se count. Defendant moved for a new trial, arguing he should have been permitted to introduce partition ratio evidence to rebut the presumption that he was under the influence of alcohol. (§ 23610(a)(3).) Defense counsel said his expert would testify that 30 percent of the population has a partition ratio other than 2,100 to 1. When the new trial motion was denied, defendant sought relief in the superior court‟s appellate division, claiming the exclusion of his partition ratio evidence was reversible error. The appellate division concluded partition ratio evidence is relevant and admissible but found the error harmless given the strength of the evidence supporting the jury‟s verdict.
The Court of Appeal transferred the case to itself on its own motion. That court distinguished between evidence about the variability of partition ratios in the general population and evidence showing the defendant had a nonstandard ratio.
It concluded evidence challenging the validity of the statutory 2,100-to-1 ratio was irrelevant, but evidence that this particular defendant had a different partition ratio should have been admitted. The court reasoned that if the defendant‟s own ratio differed significantly from the standard ratio, this fact could support an inference that the defendant was not actually impaired at the time of the offense. The court therefore held such personal partition ratio evidence is relevant and admissible in generic DUI cases. Although it found the defendant‟s offer of proof insufficient to determine the precise nature of the partition ratio evidence he sought to introduce, the Court of Appeal concluded that even assuming defendant intended to present evidence about his own ratio, and assuming the issue was preserved for review, any error was harmless under People v. Watson, supra, 46 Cal.2d at page 836.
The People and defendant separately petitioned for review. We granted both petitions to address the admissibility of partition ratio evidence in section 23152(a) cases.
I. The Science of Alcohol Testing
Alcohol affects the central nervous system. When ingested, it is absorbed into the blood and carried through the carotid arteries to the brain. (State v. Downie (1990) 117 N.J. 450 [569 A.2d 242, 245] (Downie); State v. Brayman (1988) 110 Wn.2d 183 [751 P.2d 294, 297] (Brayman).) After passing through the brain, alcohol travels through venous blood to the liver and heart, and from there, to the lungs, where it diffuses into alveolar air space and is exhaled in the breath. (Downie, at pp. 245-246.) As a practical matter, it is impossible to measure the amount of alcohol in a person‟s carotid arteries or brain. (Id. at p. 246; Taylor & Tayac, Forensic Chemist: Blood-Alcohol, supra, § 12.2, p. 712.) ...