Stanford Law School - Robert Crown Law Library

Filed 7/9/09

IN THE SUPREME COURT OF CALIFORNIA

THE PEOPLE,
Plaintiff and Respondent,
S157565
v.
Ct.App. 4/2 E041226
TIMMIE LANCE McNEAL,
San Bernardino County
Defendant and Appellant.
Super. Ct. No. TRE038083

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).)1 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).)2 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

1
All unspecified statutory references are to the Vehicle Code.
2
If blood and breath tests are not available, the driver‟s blood-alcohol
content is determined from a urine test. (§ 23612, subds. (a)(1)(A), (d)(2).)
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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.
BACKGROUND
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
2

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blew into the machine five times but produced only two samples sufficient for
testing.3 Both valid samples registered a blood-alcohol level of 0.10 percent.
Defendant was charged with both generic and per se DUI.4 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

3
The test was administered using a Draeger Alcotest 7110 machine. To
produce a valid sample for this machine, the subject must exhale at least 1.5 liters
of breath over at least 4.5 seconds. (Taylor & Tayac, Cal. Drunk Driving Defense
(4th ed. 2008) Forensic Chemist: Blood-Alcohol, § 12.40, p. 874 (hereafter Taylor
& Tayac).) If the subject fails or refuses to exhale a sufficient volume of breath,
the sample is considered invalid. (Ibid.)
4
He was also cited for two infractions for failing to stop at a red light.
(§ 21453, subd. (a).)
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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.
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DISCUSSION
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.) However, most
experts agree that measurements of alcohol in venous blood or breath give a good
indication of the amount of alcohol in the brain during the post-absorptive phase.5
(Downie, at p. 246.)
When a subject blows into a breath-testing machine, the device measures
the amount of alcohol vapor expelled into alveolar spaces deep in the lungs. From
this measurement of breath alcohol, a blood-alcohol percentage can be computed
using a mathematical constant. The conversion from breath alcohol to blood
alcohol is based on the chemistry principle of “Henry‟s law,” which holds that
there is “a constant ratio between the concentration of alcohol in the blood and the
concentration of alcohol in the alveolar air of the lungs.” (Taylor & Tayac,
Forensic Chemist: Blood-Alcohol, supra, § 12.19, p. 770.) Breath-testing

5
As the body absorbs ingested alcohol, blood-alcohol levels rise until they
reach a peak. The rate of absorption depends on many variables, including the
amount of food in the stomach, the amount of alcohol consumed, the time over
which it was consumed, and numerous individual factors. (Downie, supra, 569
A.2d at pp. 245-246; Taylor & Tayac, Forensic Chemist: Blood-Alcohol, supra,
§ 12.2, pp. 712-714.) During active absorption, blood-alcohol levels are highest in
arterial blood. (Downie, at p. 246; Taylor & Tayac, § 12:2, p. 712.) The post-
absorptive phase occurs after the blood-alcohol level has peaked and begun to
decline.
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machines in California use a conversion factor of 2,100 to 1, meaning “the amount
of alcohol in 2,100 milliliters of alveolar breath is equivalent to the amount of
alcohol in 1 milliliter of blood.” (Cal. Code Regs., tit. 17, § 1220.4, subd. (f); see
People v. McDonald (1988) 206 Cal.App.3d 877, 880.) This ratio is used,
apparently without exception, in breath-testing devices throughout the United
States. (See Brayman, supra, 751 P.2d at p. 297; State v. McManus (1989) 152
Wis.2d 113 [447 N.W.2d 654, 656].)
Nevertheless, courts here and across the country have long recognized that
actual partition ratios vary, both among members of the population and within a
single individual. In Bransford, supra, 8 Cal.4th at page 889, we noted that an
individual‟s ratio of breath-alcohol to blood-alcohol concentration can be
influenced by many variables, including “body temperature, atmospheric pressure,
medical conditions, sex, and the precision of the measuring device. [Citations.]”
(See also Brayman, supra, 751 P.2d at p. 297 [mentioning, in addition to these
factors, hematocrit level and elapsed time between drinking and breath-alcohol
measurement].) Experts have also described a wide range of variability in
partition ratios throughout the general population. In People v. McDonald, supra,
206 Cal.App.3d at page 880, for example, the people‟s expert testified a person‟s
ratio could be as high as 2,700 to 1 or as low as 1,550 to 1, and in Downie, supra,
569 A.2d at page 247, the court noted that partition ratios measured in a group of
experimental subjects ranged from a low of 1,706 to 1 to a high of 3,063 to 1.
Despite this recognized variability, most scientists agree that the 2,100-to-1
ratio roughly approximates or even underestimates the ratio of most people. In the
late 1980‟s, the New Jersey Supreme Court considered evidence presented by ten
experts at a hearing addressing partition ratios and the reliability of breath test
results. (Downie, supra, 569 A.2d at pp. 243-244.) These experts “generally
agreed” that breath-testing machines using the 2,100-to-1 partition ratio “will
usually underestimate the amount of alcohol in the blood” for several reasons. (Id.
at p. 247.) “First, most people‟s partition ratios may be closer to 2300:1 than to
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2100:1. Second, the breathalyzer results are truncated, or the third decimal
position is dropped when read. If a person reads .099 on the breathalyzer, the
results will be shortened to read .09, thereby underestimating the breath alcohol.
Third, a suspect may not provide enough deep breath to register all of the alcohol
present in the alveolar air. Fourth, the breathalyzer‟s scale is set .003 below the
start line and this gives suspects an added benefit.” (Ibid.) Several experts opined
that the standard partition ratio is set artificially low, and the true mean ratio in the
population is closer to 2,300 to 1. (Id. at p. 247.) Dr. Robert Borkenstein,
inventor of the breathalyzer machine, stated that “breathalyzer researchers and
members of the National Safety Council adopted the 2100:1 partition ratio instead
of the more accurate 2300:1 ratio because they wanted to err on the low side and
have almost no errors on the high side.” (Id. at p. 247.)6
II.
Development of California Law Regarding Partition Ratio Evidence
California‟s first drunk driving statute, enacted in 1913, prohibited any
“intoxicated person” from driving a motor vehicle on a public highway. (Stats.
1913, ch. 326, § 17, p. 646; see Burg v. Municipal Court (1983) 35 Cal.3d 257,
262.) The prohibition was later redefined as driving “under the influence” of
alcohol. “To be „under the influence‟ within the meaning of the Vehicle Code, the
liquor or liquor and drug(s) must have so far affected the nervous system, the
brain, or muscles as to impair to an appreciable degree the ability to operate a

6
See also People v. Lepine (1989) 215 Cal.App.3d 91, 94 (defense expert
testified that the average partition ratio is 2,286 to 1); People v. Pritchard (1984)
162 Cal.App.3d Supp. 13, 16 (people‟s expert testified that 95 percent of the
population falls within the range of 2,100 to 1, plus or minus a 10 percent margin
of error); People v. Gustafson (1990) 194 Ill.App.3d 910 [551 N.E.2d 826, 829]
(state‟s expert testified “he believed the 2,100:1 ratio was applicable to at least 95
[percent] of the population”); State v. McManus, supra, 447 N.W.2d at pages 656-
657 (noting “the 2,100:1 ratio has been shown to either correctly estimate or
underestimate a person‟s corresponding blood alcohol concentration with 94
percent accuracy”); Brayman, supra, 751 P.2d at page 300 (citing studies
indicating breath tests underestimate blood-alcohol levels 80 to 91 percent of the
time and overestimate them only 5 to 6 percent of the time).
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vehicle in a manner like that of an ordinarily prudent and cautious person in full
possession of his faculties. [Citations.]” (Byrd v. Municipal Court (1981) 125
Cal.App.3d 1054, 1058, italics omitted.) In 1969 the Legislature enacted a
statutory presumption that a driver was under the influence if the driver‟s blood
contained 0.10 percent or more, by weight, of alcohol. (Stats. 1969, ch. 231, § 1,
p. 565; Burg v. Municipal Court, at p. 263.) However, “[e]ven these laws, which
considerably assisted the prosecution of „driving under the influence‟ cases,
proved inadequate in many respects. Under them, the ultimate question was
defined in terms of the defendant‟s subjective behavior and condition: „Was the
defendant under the influence at the time he drove?‟ Celerity and certainty of
punishment were frustrated by the ambiguity of the legal criteria; no matter what
his blood-alcohol level, a defendant could escape conviction merely by raising a
doubt as to his intoxication. [Citations.]” (Burg v. Municipal Court, at p. 263.)
These difficulties led the Legislature to create a new crime. Section 23152(b),
added in 1981, made it unlawful for a person to drive with a blood-alcohol level of
0.10 percent or more, by weight, and specified that, “percent, by weight, of
alcohol shall be based upon grams of alcohol per 100 milliliters of blood.” (Stats.
1981, ch. 940, § 33, p. 3578.) To secure a conviction for this new “per se DUI”
offense, the prosecution no longer had to prove the accused driver was actually
impaired at the time of the offense, but only that he drove with a blood-alcohol
level at or exceeding 0.10 percent. (Burg v. Municipal Court, at p. 265.) In 1989,
the Legislature further strengthened our state‟s DUI laws by lowering the
punishable blood-alcohol threshold from 0.10 percent to 0.08 percent. (Stats.
1989, ch. 1114, § 27, p. 4080; see People v. Ireland (1995) 33 Cal.App.4th 680,
689.)
Thus, after 1981 there were two parallel statutes making it a crime to drive
while intoxicated. The generic DUI provision (§ 23152(a)) retained the historical
approach, requiring proof that the defendant was actually impaired by his
drinking. The per se DUI statute (§ 23152(b)) simply required proof that the
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defendant had been driving with a blood-alcohol level over the legal limit. If the
limit was exceeded, the statute was violated, and no additional proof of the
defendant‟s impairment was required.
Throughout this time, both the per se DUI offense and the presumption of
intoxication applicable to the generic DUI offense were defined based on
measurements of blood alcohol. As a result, whenever a defendant elected to have
a breath test instead of a blood draw, it was necessary to convert the breath results
into an equivalent blood-alcohol percentage. (Bransford, supra, 8 Cal.4th at
pp. 888-889; People v. Ireland, supra, 33 Cal.App.4th at p. 689.) A Department
of Health Services regulation required that this conversion be made using a
partition ratio of 2,100 to 1. (Cal. Code Regs., tit. 17, § 1220.4, subd. (f).)7
The mandated use of a standard partition ratio, in the face of scientific
knowledge that such ratios vary greatly, provided fertile ground for defense
arguments challenging the reliability of breath test results. Initially, courts
permitted defendants to show only that their personal partition ratio differed from
the norm. (Bransford, supra, 8 Cal.4th at p. 889.) Applying the judicially created
“rule of convenience,” these courts placed the burden on the defendant to produce
evidence of a nonstandard personal ratio because this fact was considered to be
peculiarly within the defendant‟s knowledge. (People v. Pritchard, supra, 162
Cal.App.3d at p. Supp. 16; People v. Gineris (1984) 162 Cal.App.3d Supp. 18, 23;
People v. Herst (1987) 197 Cal.App.3d Supp. 1, 3-4.)
Later courts questioned this application of the rule of convenience when
confronted with evidence showing that an individual‟s partition ratio can vary
from time to time due to the influence of numerous external factors. (See, e.g.,
People v. McDonald, supra, 206 Cal.App.3d at p. 883.) This evidence directly

7
“A breath alcohol concentration shall be converted to an equivalent blood
alcohol concentration by a calculation based on the relationship: the amount of
alcohol in 2,100 milliliters of alveolar breath is equivalent to the amount of
alcohol in 1 milliliter of blood.” (Cal. Code Regs., tit. 17, § 1220.4, subd. (f).)
9

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contradicted something the Pritchard line of cases had apparently assumed: “that
one‟s partition ratio is constant and can be measured by the defendant.” (Ibid.; see
also People v. Lepine, supra, 215 Cal.App.3d at pp. 97-99.) Because partition
ratios may vary depending on many factors, reliable measurements may be
difficult and costly to acquire. Thus, some courts reasoned that defendants did not
have substantially better access to evidence of their personal partition ratios and
could not be expected to carry the burden of production on the issue. (People v.
McDonald, at p. 883; People v. Lepine, at pp. 99-101; People v. Thompson (1989)
215 Cal.App.3d Supp. 7, 13.) Further, having freed defendants from the rule of
convenience, these courts saw no reason to exclude general partition ratio
evidence describing the variability of partition ratios among the general
population. (People v. Lepine, at p. 100; People v. Thompson, at pp. Supp. 13-14;
People v. Cortes (1989) 214 Cal.App.3d Supp. 12, 18.) After citing a string of
out-of-state decisions permitting such evidence, one court reasoned: “[I]t seems
clear from the evidence submitted in this case and from a host of opinions in this
and other states, that the partition ratio may vary from time to time and from
individual to individual. This being the case it is appropriate a jury be allowed to
consider that fact. We trust in the general rules of evidence, the preparation of
counsel and the good judgment of trial judges to insure that this question of
partition ratio variability is presented to jurors in a proper, complete and
understandable form.” (People v. Lepine, at p. 100, fn. omitted.)
The Legislature responded swiftly to these developments. In April 1989,
legislators amended a pending Senate Bill on a related topic to specify for
purposes of the per se DUI offense and the presumption of intoxication that the
percentage of alcohol in a person‟s blood is to be based upon grams of alcohol per
100 milliliters of blood “or grams of alcohol per 210 liters of breath.” (Sen.
Amend. to Sen. Bill No. 1119 (1989-1990 Reg. Sess.) Apr. 27, 1989, p. 23; Stats.
1989, ch. 1114, §§ 24-25, pp. 4078-4079 [amending § 23152(b)]; Sen. Amend. to
Sen. Bill No. 1119 (1989-1990 Reg. Sess.) Apr. 27, 1989, p. 26; Stats. 1989,
10

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ch. 1114, §§ 34-35, pp. 4085-4086 [amending former § 23155, subd. (b)].) In so
doing, the Legislature codified 2,100 to 1 as the partition ratio to be used in
converting breath test results into blood-alcohol levels.
As we observed in Bransford, supra, 8 Cal.4th at page 890, scant
explanation for these amendments appears in the legislative history of Senate Bill
No. 1119, but more illumination can be found in the history of Assembly Bill
No. 4318 (1989-1990 Reg. Sess.), enacted as Statutes 1990, chapter 708, section 1,
page 3289. The purpose of Assembly Bill No. 4318 was to accelerate the effective
date of the partition ratio amendments to section 23152(b) that had been enacted
by passage of Senate Bill No. 1119. (Assem. Com. on Public Safety, com. on
Assem. Bill No. 4318 (1989-1990 Reg. Sess.) as introduced May 15, 1990; see
People v. Ireland, supra, 33 Cal.App.4th at p. 691.) Committee reports
concerning this bill evince the Legislature‟s desire to prohibit challenges to breath
test results based on the partition ratio. For example, the Assembly Committee on
Public Safety observed that “[a]ttacks on the partition ratio may result in
expensive and time consuming evidentiary hearings and undermine successful
enforcement of driving under the influence laws.” (Assem. Com. on Public
Safety, com. on Assem. Bill No. 4318 (1989-1990 Reg. Sess.) as introduced May
15, 1990, p. 2.) The express purpose of Assembly Bill No. 4318 was to
“[e]liminate the need for conversion of a breath quantity to a blood concentration
of alcohol by statutorily defining driving under the influence in terms of the
concentration of alcohol found in the breath when breath analysis is used.” (Ibid.;
see also Sen. Rules Com., Off. of Sen. Floor Analyses, Rep. on Assem. Bill
No. 4318 (1989-1990 Reg. Sess.) Aug. 9, 1990, p. 1.)
The Legislature accomplished this purpose by defining the offense of per se
DUI in terms of a prohibited level of blood alcohol or breath alcohol. As we
explained in Bransford, supra, 8 Cal.4th at page 890, the amendment of
section 23152(b) providing for an alternative measurement based upon breath
changed the definition of the offense. In the per se DUI statute, the Legislature
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has set a legal limit on permissible blood alcohol and has defined how that limit is
to be measured in a breath sample. If the limit, measured as the statute sets out, is
exceeded, the statute has been violated. Because section 23152(b) now defines the
offense of per se DUI as the presence of a prohibited level of alcohol in either 100
milliliters of blood or 210 liters of breath, a conversion from breath to blood-
alcohol concentration is no longer required to establish guilt. Accordingly,
evidence attacking the standard partition ratio is no longer relevant in a per se DUI
prosecution because the Legislature has codified the 2,100-to-1 ratio as part of the
offense. (Bransford, at pp. 890-892.)
Assembly Bill No. 4318 did not amend former section 23155, however.8
The bill amended only the per se DUI offense (§ 23152(b)) and a similar offense
of per se DUI causing bodily injury (§ 23153, subd. (b)). (Stats. 1990, ch. 708,
§§ 1-4, pp. 2870-2872.) Thus, committee statements reflecting the Legislature‟s
desire to end the conversion of breath results to blood alcohol were all made in
regard to changing the definition of the per se DUI offense. No legislative history
clarifies exactly what the Legislature intended when it amended the presumption
of intoxication applicable to generic DUI cases
III.
Admissibility of Partition Ratio Evidence in Generic DUI Cases
Despite our holding in Bransford that partition ratio evidence is
inadmissible in per se DUI cases, defendant argues partition ratio variability
evidence should be admissible in generic DUI cases to rebut the presumption that
a person who produces a certain breath result is actually “under the influence” of
alcohol. (§§ 23152(a); 23610(a)(3).) This issue was not presented in Bransford,
and we specifically declined to consider it. (Bransford, supra, 8 Cal.4th at p. 893,
fn. 10.) Defendant‟s claim does involve the same statutory language we
interpreted in Bransford: “Percent, by weight, of alcohol in the person‟s blood

8
As a result, partition ratio amendments to the statutory presumption of
intoxication did not go into effect until January 1, 1992, the operative date set
forth in Senate Bill No. 1119.
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shall be based upon grams of alcohol per 100 milliliters of blood or grams of
alcohol per 210 liters of breath.” (§ 23610(b); see Bransford, at p. 890, quoting
§ 23152(b).) However, in Bransford this language was used in the definition of a
criminal offense. Here, it is part of a rebuttable presumption. The question is
whether a defendant who has a blood-alcohol concentration of 0.08 percent or
more measured by breath is entitled to rebut the presumption that he was “under
the influence” in a section 23152(a) case by introducing evidence that use of a
2,100-to-1 partition ratio may have produced an inaccurate measure of his blood
alcohol.
The Legislature passed section 23152(b) to facilitate the prosecution of
drunk drivers. The creation of a per se DUI offense did away with the need to
prove the defendant was actually impaired. However, impairment must still be
proven for a charge of generic DUI under section 23152(a). In a generic DUI
case, section 23610 creates a rebuttable presumption that the defendant was under
the influence of alcohol if a chemical test measures his blood-alcohol
concentration at 0.08 percent or higher. As relevant here, section 23610 states:
“(a) Upon the trial of any criminal action, or preliminary proceeding in a
criminal action, arising out of acts alleged to have been committed by any person
while driving a vehicle while under the influence of an alcoholic beverage in
violation of subdivision (a) of Section 23152 or subdivision (a) of Section 23153,
the amount of alcohol in the person‟s blood at the time of the test as shown by
chemical analysis of that person‟s blood, breath, or urine shall give rise to the
following presumptions affecting the burden of proof: [¶] . . .[¶]
“(3) If there was at that time 0.08 percent or more, by weight, of alcohol in
the person‟s blood, it shall be presumed that the person was under the influence of
an alcoholic beverage at the time of the alleged offense.[9]

9
Deleted subdivisions state that a blood-alcohol level between 0.05 and 0.08
gives rise to no presumption, and a blood-alcohol level under 0.05 gives rise to a
presumption that the driver was not under the influence. (§ 23610(a)(1)-(2).)
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“(b) Percent, by weight, of alcohol in the person‟s blood shall be based
upon grams of alcohol per 100 milliliters of blood or grams of alcohol per 210
liters of breath.
“(c) This section shall not be construed as limiting the introduction of any
other competent evidence bearing upon the question of whether the person
ingested any alcoholic beverage or was under the influence of an alcoholic
beverage at the time of the alleged offense.”
Although section 23610 applies to chemical testing of the driver‟s blood,
breath, or urine, the presumption of intoxication arises only if the testing shows
the presence of 0.08 percent or more of alcohol in the driver‟s blood.
(§ 23610(a)(3).) The statute is not written to invoke a presumption based on a
certain blood result or breath result; it is framed in terms of blood alcohol only.
Thus, if the prosecution is relying on the result of a breath test, the breath result
must be converted into a blood-alcohol equivalent for the section 23610
presumption to apply. Subdivision (b) sets this conversion factor at a ratio of 210
liters of breath to 100 milliliters of blood.
The logic of the presumption proceeds as follows. The Legislature has
concluded that most people with a blood-alcohol concentration at or above
0.08 percent are too impaired to operate a vehicle safely. Breath tests are a
convenient way to measure a suspect‟s alcohol consumption, and they can be
converted into an equivalent blood-alcohol level by applying a mathematical ratio.
A conversion ratio of 2,100 to 1 is a safe standard to use because, for most people,
it will produce an accurate or slightly low measure of alcohol in the blood. (See,
e.g., People v. Lepine, supra, 215 Cal.App.3d at p. 94; Downie, supra, 569 A.2d at
p. 247; Brayman, supra, 751 P.2d at p. 300.) Thus, if a driver‟s breath test shows
a converted blood-alcohol level of 0.08 percent or more, the measurement is
generally accurate and may fairly be used to prove the driver was actually under
the influence, as the generic DUI statute requires. Other evidence of actual
impairment may include the driver‟s appearance, an odor of alcohol, slurred
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speech, impaired motor skills, slowed or erratic mental processing, and impaired
memory or judgment. Conversely, absence of these manifestations may indicate
that the driver was not impaired.
With regard to the inference to be drawn from a breath result, the question
of whether a defendant‟s converted blood-alcohol level is accurate depends upon
the validity of the 2,100-to-1 partition ratio. If the defendant‟s own partition ratio
is the same as or higher than this standard ratio, his converted blood-alcohol result
is valid or skewed in his favor. If, however, the defendant‟s own partition ratio at
the time of testing is lower than the standard ratio, conversion of the breath result
using the statutory formula produces an artificially high measure of his blood
alcohol.
Evidence that a defendant has a comparatively low partition ratio would
thus tend to show that a blood-alcohol concentration calculated with the standard
2,100-to-1 ratio overstates the actual amount of alcohol in his blood. For someone
with an extremely low ratio of 1,100 to 1, for example, use of the 2,100-to-1
partition ratio would overstate blood-alcohol content by almost 50 percent. (See
State v. Burling (1987) 224 Neb. 725 [400 N.W.2d 872, 876-877].)10 Evidence
showing the defendant had a low partition ratio, and thus a lower concentration of
blood alcohol than was reported, could also support an inference that he was not
under the influence in violation of the generic DUI law. In addition, evidence
about the variability of partition ratios in the general population is relevant to raise
a reasonable doubt about the accuracy of a defendant‟s converted blood-alcohol
level. Because partition ratios vary among individuals and the 2,100-to-1 ratio
used by breath-testing machines is based on an average, there is a possibility that

10
Burling‟s holding that a breath test result must be reduced to 52.38 percent
of the machine‟s reading (to reflect this potential margin of error) has been
overruled by Nebraska‟s high court. (State v. Baue (2000) 258 Neb. 968 [607
N.W.2d 191, 200-201].)
15

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the blood-alcohol level such a machine produces for a given defendant is
inaccurate.
The People contend the Legislature rendered partition ratio evidence
irrelevant when it amended section 23610(b) to state that blood-alcohol
percentages “shall be based upon grams of alcohol per 100 milliliters of blood or
grams of alcohol per 210 liters of breath.” According to the People‟s reasoning,
because the Legislature has placed a partition ratio in section 23610, no evidence
can be offered to contradict or question that ratio in a particular case. Evidence
that the defendant may have a different ratio is irrelevant, the People assert,
because the Legislature has spoken and established 2,100 to 1 as the ratio to be
used in every case. Our reasoning was similar when we construed the partition
ratio amendments to section 23152(b) in Bransford, supra, 8 Cal.4th at page 892,
but the People‟s attempt to apply Bransford here overlooks an important
difference in context. As noted, in Bransford, we were construing language in a
statute that defines an offense. Section 23512(b) makes it a crime to drive with a
blood-alcohol content of 0.08 percent or more as measured in grams of alcohol per
100 milliliters of blood or per 210 liters of breath. The crime itself is defined in
terms of a prohibited blood or breath result. Here, we are considering language in
a statute that describes a rebuttable presumption. Section 23610 permits, but does
not require, the jury to infer that the defendant was under the influence if he had a
blood-alcohol level of 0.08 percent or more. (See People v. Milham (1984) 159
Cal.App.3d 487, 505; see also CALJIC No. 12.61; CALCRIM No. 2110.)
Although section 23610(b) incorporates the same conversion factor for breath test
results as appears in section 23152(b), here this factor is not part of the definition
of an offense and, like the rest of the presumption, it is rebuttable.
Moreover, section 23610 specifically mandates that it “shall not be
construed as limiting the introduction of any other competent evidence bearing
upon the question of whether the person ingested any alcoholic beverage or was
under the influence of an alcoholic beverage at the time of the alleged offense.”
16

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(§ 23610, subd. (c).) Thus, even in light of the presumption, a defendant charged
under the generic 23152(a) provision is entitled to offer “other competent
evidence” relevant to whether he was actually under the influence of alcohol.11
Competent evidence that the 2,100-to-1 ratio does not accurately reflect the
partition ratio for all people, or that the defendant‟s partition ratio may have been
lower, is relevant to this question. “ „Relevant evidence‟ means evidence . . .
having any tendency in reason to prove or disprove any disputed fact that is of
consequence to the determination of the action.” (Evid. Code, § 210.) The central
disputed fact in a generic DUI prosecution is whether the defendant was under the
influence of alcohol while driving. The chemical test result is circumstantial
evidence that supports an inference regarding that disputed fact. Specifically,
when a defendant‟s breath test result is equivalent to 0.08 percent or more of blood
alcohol, section 23610 permits the jury to infer he was indeed under the influence
of alcohol. The defendant is entitled to challenge this inference and can do so by,
among other things, raising a reasonable doubt as to whether the test result was an
accurate measure of his blood-alcohol level. Evidence casting doubt on the
accuracy of the breath-to-blood conversion ratio is just as relevant as other
evidence rebutting the presumption of intoxication from a breath test result, such

11
The People assert that by “other competent evidence” the statute is referring
to evidence “other” than the partition ratio set forth in subdivision (b). This overly
narrow reading does not follow from the plain language of the statute. Clearly, the
import of subdivision (c) is to preserve a defendant‟s ability to rebut the
presumption, not to limit the type of evidence that can be introduced. Moreover,
the People‟s interpretation of subdivision (c) makes little sense given that the
subdivision existed in essentially its present form before the breath provision was
added to subdivision (b). (Former § 23126, subd. (c), added by Stats. 1969,
ch. 231, § 1, p. 565 [“The foregoing provisions shall not be construed as limiting
the introduction of other competent evidence bearing upon the question whether
the person was under the influence of intoxicating liquor at the time of the alleged
offense”].) The reference to “other competent evidence” cannot have meant
“other than the partition ratio” when no partition ratio was specified.
17

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as evidence that the defendant had a high tolerance for alcohol or performed well
in field sobriety testing.
Accordingly, we hold that evidence about partition ratio variability is
relevant in generic DUI cases to rebut the presumption of intoxication in
section 23610. Although the Court of Appeal distinguished between “general”
and “personal” partition ratio evidence, concluding only the latter is potentially
admissible, this distinction does not survive close scrutiny. Both types of evidence
challenge the accuracy of a defendant‟s reported blood-alcohol level, and therefore
both can be used to support an inference that, despite a high breath test result, the
defendant was not under the influence. Although the inference is less direct when
the evidence is not tied to the defendant, and concerns only variability of partition
ratios in the population at large, indirectness alone is not a reason to exclude
evidence that is logically relevant to a defense.
We do agree with the Court of Appeal, however, that partition ratio
evidence may not be used to negate the basic fact triggering the section 23610
presumption, and thereby defeat operation of the presumption itself. Because
section 23610 expressly incorporates a 2,100-to-1 partition ratio, the defendant
may not argue the presumption does not apply because a different ratio should
have been used. The result of the statutorily mandated test remains admissible,
and the jury is still properly instructed on the presumption. Defense evidence is
relevant to rebut the presumption that the defendant was intoxicated, but not to
remove the presumption altogether.
Our decision is in accord with those of the two other state courts that have
discussed the admissibility of partition ratio evidence in generic DUI cases. In
State v. Hanks (2001) 172 Vt. 93, 96 [772 A.2d 1087, 1089] (Hanks), the Vermont
Supreme Court considered the effect of a statute that defined “alcohol
concentration” for purposes of the state‟s DUI laws to mean grams of alcohol per
100 milliliters of blood or per 210 liters of breath. The defendant in Hanks
conceded this statute may have made evidence about partition ratio variability
18

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inadmissible in cases alleging a violation of the state‟s per se DUI law, but he
argued such evidence was still relevant in cases alleging the defendant drove
“under the influence of intoxicating liquor” in violation of the generic DUI law.
(Id. at pp. 1088, 1091.) The Vermont Supreme Court agreed. (Id. at p. 1091.)
The court observed that “any evidence raising a doubt as to the defendant‟s
condition, which is the ultimate question in a generic DWI prosecution . . . is
relevant and admissible.” (Id. at p. 1092, italics added.) Like California, Vermont
has a statutory presumption that permits the jury to infer a person with a blood-
alcohol concentration of 0.08 percent or more was under the influence of alcohol
at the time of the offense. (23 Vt. Stat. Ann. § 1204, subd. (a)(2); see Hanks, at
p. 1088.) The Hanks court explained that evidence about partition ratio variability
is relevant to rebut this inference because it could cast doubt on the accuracy of
the breath test result as an indicator of the defendant‟s impairment. (Hanks, at
p. 1092.) Finally, the court observed, where the “defendant is charged with
driving while under the influence rather than driving with an alcohol concentration
exceeding the statutory limit, admitting scientifically accepted evidence
concerning the variability of partition ratios will not negate a statutory offense or
even an element of a statutory offense; rather, it will merely allow defendant to
challenge the permissive inference and the State‟s charge that he was impaired.”
(Id. at pp. 1092-1093.)
An Arizona appellate court considered the same question, in light of similar
statutes, and concluded evidence about partition ratio variability “is not relevant to
a prosecution for per se DUI, but may be relevant to a prosecution for traditional
DUI if, in the latter instance, the State introduces evidence of the defendant‟s
breath alcohol level to support conviction.” (Guthrie v. Jones (Ariz.Ct.App.
2002) 202 Ariz. 273, 274 [43 P.3d 601, 602] (Guthrie).) The court reasoned that
when the prosecution relies on a breath test result to invoke Arizona‟s statutory
presumption that the defendant was under the influence of alcohol (Ariz. Rev.
Stat. § 28-1381, subd. (G)), partition ratio evidence casting doubt on that
19

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presumption is relevant and admissible. (Guthrie, at p. 604.) The Guthrie court
relied in part on statutory language similar to our section 23610, subdivision (c),
concluding that the statute “does not limit the introduction of any other competent
evidence bearing on the question of whether or not the defendant was under the
influence of intoxicating liquor.” (Ariz. Rev. Stat. § 28-1381, subd. (H); Guthrie,
at p. 604.)
We reach the same conclusion as the Vermont and Arizona courts. If the
defendant in a section 23152(a) case offers competent evidence showing that the
use of a 2,100-to-1 conversion ratio may have yielded an inaccurate representation
of his blood-alcohol level, introduction of this evidence is permissible. In light of
this decision, we need not consider whether a contrary interpretation of
section 23610 would raise constitutional concerns. (See Santa Clara County
Local Transportation Authority v. Guardino (1995) 11 Cal.4th 220, 230 [the court
will not decide constitutional questions where other grounds are available and
dispositive]; see also Lyng v. Northwest Indian Cemetery Prot. Assn. (1988) 485
U.S. 439, 445.)
Naturally, the proffered evidence must still satisfy standards of competence
and all other applicable evidentiary requirements. We do not here consider how a
party might establish partition ratio variability in general or in regard to an
individual. In particular, we express no opinion as to whether evidence of an
individual‟s personal partition ratio has gained sufficient acceptance in the
scientific community to be admissible. (See People v. Kelly (1976) 17 Cal.3d 24,
30-32.)
In addition, like all other evidence, partition ratio evidence must be timely
offered. Here, defendant attempted to introduce this evidence only after both sides
had rested. His motion to reopen was one addressed to the court‟s sound
discretion. (People v. Jones (2003) 30 Cal.4th 1084, 1110; People v. Marshall
(1996) 13 Cal.4th 799, 836.) We need not discuss this procedural question further.
Like the Court of Appeal, we may assume that defendant could have made an
20

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adequate offer of proof, to be presented by a competent witness, and that the trial
court would have allowed him to reopen. Nevertheless, defendant is not entitled
to a reversal here, because any error in excluding the partition ratio evidence was
harmless.
“As a general matter, the „[a]pplication of the ordinary rules of evidence . . .
does not impermissibly infringe on a defendant‟s right to present a defense.‟
[Citations.]” (People v. Fudge (1994) 7 Cal.4th 1075, 1102-1103.) Because the
trial court merely rejected some evidence concerning a defense, and did not
preclude defendant from presenting a defense, any error is one of state law and is
properly reviewed under People v. Watson, supra, 46 Cal.2d at page 836. (People
v. Fudge, at p. 1103.) Having examined all the evidence, we conclude it is not
reasonably probable defendant would have achieved a more favorable result
absent the exclusion of partition ratio evidence.
The question for the jury was whether defendant was under the influence of
alcohol when he drove through two red lights. Defendant was stopped at 11:00
p.m. When asked to produce his driver‟s license, he initially could not find it.
Asked why he ran the lights, defendant replied, at first, that he was chasing
someone who had threatened him with a gun. Later, he said he was looking for his
wife, or that his wife was following right behind him. The arresting officer saw no
one else around. Defendant‟s eyes were watery and bloodshot, his speech was
slurred, and a strong odor of alcohol came from the interior of his car and from his
person. His face was flushed and he had difficulty answering questions. When he
got out of his car, he leaned on the vehicle for support as he made his way to the
sidewalk. Defendant said he had consumed one beer and had taken medication
that morning for diabetes; however, no evidence offered at trial showed defendant
was diabetic. Defendant failed every one of the field sobriety tests he tried to
perform. A preliminary alcohol screening test given at the scene showed the
presence of alcohol in his breath. Based on defendant‟s driving, appearance, and
21

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performance on the field sobriety tests, the arresting officer formed an opinion that
defendant was impaired due to the influence of alcohol.
In addition to this significant evidence of defendant‟s intoxication, the
jury‟s verdict also indicates that the admission of partition ratio evidence was not
reasonably likely to have produced a more favorable result. (See People v.
Watson, supra, 46 Cal.2d at p. 836.) Although they found him guilty of generic
DUI, the jury could not agree whether defendant was also guilty of per se DUI.
They reported an unspecified split of “five to seven” on this issue. Thus, even
without partition ratio evidence, nearly half the jury rejected the accuracy of
defendant‟s breath test result and declined to find that he had exceeded the legal
limit of 0.08 percent blood alcohol. Nevertheless, all jurors believed defendant
was “under the influence” for purposes of section 23152(a). It is difficult to
imagine that the jurors who rejected defendant‟s breath result in considering the
per se DUI charge would have relied on this result, and the section 23610
presumption, to convict him of the generic DUI charge.
DISPOSITION
The judgment of the Court of Appeal is affirmed.
CORRIGAN, J.
WE CONCUR: GEORGE, C. J.

KENNARD, J.
BAXTER, J.
WERDEGAR, J.
CHIN, J.
MORENO, J.
22

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See next page for addresses and telephone numbers for counsel who argued in Supreme Court.

Name of Opinion People v. McNeal
__________________________________________________________________________________

Unpublished Opinion

Original Appeal
Original Proceeding
Review Granted XXX 155 Cal.App.4th 582
Rehearing Granted

__________________________________________________________________________________

Opinion No.

S157565
Date Filed: July 9, 2009
__________________________________________________________________________________

Court:

Superior
County: San Bernardino
Judge: Michael A. Smith

__________________________________________________________________________________

Attorneys for Appellant:

Jamie L. Popper, under appointment by the Supreme Court, and Linn Davis, under appointment by the
Court of Appeal, for Defendant and Appellant.

Darryl W. Genis for California DUI Lawyers Association, David Stanford, Marta Gajewski, Lyle Clayton
Turner and Ronald Audia as Amici Curiae on behalf of Defendant and Appellant.

__________________________________________________________________________________

Attorneys for Respondent:

Michael A. Ramos, District Attorney, Mark A. Vos, Lead Deputy District Attorney, and Astrid G. Alfonso,
Deputy District Attorney, for Plaintiff and Respondent.

Bonnie M. Dumanis, District Attorney (San Diego); Albert C. Locher, Assistant District Attorney
(Sacramento); Margaret O‟Malley, Deputy District Attorney (Santa Barbara); and W. Scott Thorpe for
California District Attorneys Association as Amicus Curiae on behalf of Plaintiff and Respondent.

---

Counsel who argued in Supreme Court (not intended for publication with opinion):

Jamie L. Popper
555 West Beech Street, Suite 300
San Diego, CA 92101
(619) 696-0282

Mark A. Vos
Lead Deputy District Attorney
412 Hospitality Lane, First Floor
San Bernardino, CA 92415
(909) 382-7629

Margaret O‟Malley
Deputy District Attorney
1112 Santa Barbara Street
Santa Barbara, CA 93101
(805) 568-2300

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Petition for review after the Court of Appeal affirmed a judgment of conviction of a criminal offense. This case presents the following issues: (1) Should evidence of the range and variability between individuals of the "partition ratio," which defines the percentage of alcohol in a breath sample that corresponds to a given level of alcohol in the blood, be admissible in a prosecution for driving under the influence in violation of Vehicle Code section 23152, subdivision (a)? (2) Should evidence of a defendant's personal partition ratio be admissible in such a case?

Opinion Information

Date:	Citation:	Docket Number:	Category:	Status:
Thu, 07/09/2009	46 Cal. 4th 1183, 210 P.3d 420, 96 Cal. Rptr. 3d 261	S157565	Review - Criminal Appeal	closed; remittitur issued

Opinion Authors
Opinion	Justice Carol A. Corrigan

Disposition
Jul 9 2009	Opinion: Affirmed

Dockets
Oct 24 2007	Petition for review filed Timmie Lance McNeal, Appellant Linn Davis, Attorney
Oct 25 2007	Record requested
Oct 30 2007	Received Court of Appeal record one doghouse
Oct 31 2007	2nd petition for review filed The People, respondent Mark A. Vos, Deputy District Attorney
Nov 13 2007	Request for depublication (petition for review pending) the People, plaintiff and respondent Mark Vos, Dep. D.A.
Dec 18 2007	Time extended to grant or deny review The time for granting or denying review in the above-entitled matter is hereby extended to and including January 29, 2008 or the date upon which review is either granted or denied.
Jan 3 2008	Petition for review granted (criminal case) Votes: George, C.J., Kennard, Baxter, Chin, Moreno and Corrigan, JJ. Werdegar, J., was absent and did not participate. *note: both petitions for review granted.
Jan 31 2008	Request for extension of time filed for respondent to file the opening brief on the merits, to 2-19-08
Feb 1 2008	Extension of time granted On application of respondent and good cause appearing, it is ordered that the time to serve and file the opening brief on the merits is extended to and including February 19, 2008.
Feb 19 2008	Opening brief on the merits filed the People, plaintiff and respondent Mark Vos, Deputy District Attorney
Feb 22 2008	Counsel appointment order filed Upon request of appellant for appointment of counsel, Appellate Defenders, Inc. is hereby appointed to represent appellant on the appeal now pending in this court. Appellant's brief on the merits must be served and filed on or before 30 days from this order.
Mar 13 2008	Request for extension of time filed for appellant Mc Neal to file the answer brief on the merits (response to opening brief of the A.G.) Request for extension to 4-21-08.
Mar 13 2008	Request for extension of time filed for appellant Mc Neal to file the opening brief on the merits. request for extension to 4-23-08
Mar 20 2008	Extension of time granted On application of appellant and good cause appearing, it is ordered that the time to serve and file the answer brief on the merits is extended to and including April 21, 2008.
Mar 20 2008	Extension of time granted On application of appellant and good cause appearing, it is ordered that the time to serve and file the opening brief on the merits is extended to and including April 23, 2008.
Apr 14 2008	Request for extension of time filed for appellant to file the opening and answer briefs on the merits (as a single brief), to May 23, 2008.
Apr 22 2008	Extension of time granted On application of appellant and good cause appearing, it is ordered that the time to serve and file a combined opening and answer brief on the merits is extended to and including May 23, 2008.
May 23 2008	Received: Appellant's (oversize) combined opening brief on the merits and answer brief on the merits, with application for permission.
Jun 2 2008	Application to file over-length brief granted re appellant's combined brief
Jun 2 2008	Opening brief on the merits filed and Answer Brief on the Merits Timmie McNeal, defendant and appellant Jamie Popper, counsel
Jun 6 2008	Request for extension of time filed to file the "reply" brief on the merits, to 8-11-08 The People, plaintiff and respondent Mark Vos, Dep. District Attorney
Jun 12 2008	Extension of time granted On application of respondent and good cause appearing, it is ordered that the time to serve and file the reply brief on the merits is extended to and including August 11, 2008.
Aug 11 2008	Reply brief filed (case not yet fully briefed) the People, plaintiff and respondent Mark Vos, Dep. D.A.
Sep 4 2008	Received: Appellant's (untimely) reply brief on the merits. Accompanied by application requesting permission.
Sep 12 2008	Reply brief filed (case fully briefed) Timmie McNeal, appellant Jamie Popper, counsel filed with permission
Oct 14 2008	Received application to file Amicus Curiae Brief California DUI Lawyers Assn., David Stanford, Marta Gajewski, Lyle Turner and Senior Chief Audia [in support of aplt] ~Attorney Darryl W. Genis
Oct 14 2008	Received application to file Amicus Curiae Brief California District Attorneys Association in support of respondent Margaret O' Malley, counsel application and brief separate
Oct 29 2008	Permission to file amicus curiae brief granted The application of California DUI Lawyers Association, David Stanford, Marta Gajewski, Lyle Clayton Turner and Ronald Audia for permission to file an amicus curiae brief in support of appellant is hereby granted. An answer thereto may be served and filed by any party within twenty days of the filing of the brief.
Oct 29 2008	Amicus curiae brief filed California DUI Lawyers Association, David Stanford, Marta Gajewski, Lyle Clayton Turner and Ronald Audia, in support of appellant Darryl Genis, counsel
Oct 29 2008	Permission to file amicus curiae brief granted The application of California District Attorneys Association for permission to file an amicus curiae brief in support of respondent is hereby granted. An answer thereto may be served and filed by any party within twenty days of the filing of the brief.
Oct 29 2008	Amicus curiae brief filed California District Attorneys Association, in support of respondent Margaret O'Malley, counsel
Nov 17 2008	Response to amicus curiae brief filed Timmie McNeal, appellant Jamie Popper, counsel Response to brief of Calif. Dist. Attys Association
Nov 19 2008	Response to amicus curiae brief filed The People, respondent Mark Vos, Dep. D.A. Response to brief of Calif. DUI Lawyers Association (timely-CRC 8.25b)
Apr 1 2009	Case ordered on calendar to be argued Tuesday, May 5, 2009, at 9:00 a.m., in San Francisco
Apr 1 2009	Order filed For purposes of oral argument, appellant will argue first and may reserve time for rebuttal; respondent will argue second.
Apr 16 2009	Filed: Letter from Mark A. Vos, counsel for respondent The People, requesting to share 10 minutes of oral argument time with amicus curiae California District Attorneys Association.
Apr 20 2009	Order filed The request of counsel for respondent in the above-referenced cause to allow two counsel to argue on behalf of respondent at oral argument is hereby granted. The request of respondent to allocate to amicus curiae California District Attorneys Association 10 minutes of respondent's 30-minute allotted time for oral argument is granted.
May 5 2009	Cause argued and submitted
Jul 8 2009	Notice of forthcoming opinion posted
Jul 9 2009	Opinion filed: Judgment affirmed in full The judgment of the Court of Appeal is affirmed. Majority Opinion by Corrigan, J. -----joined by George, C.J., Kennard, Baxter, Werdegar, Chin and Moreno, JJ.
Jul 22 2009	Compensation awarded counsel Atty Popper - Appellate Defenders, Inc
Aug 11 2009	Remittitur issued

Briefs
Feb 19 2008	Opening brief on the merits filed the People, plaintiff and respondent Mark Vos, Deputy District Attorney
Jun 2 2008	Opening brief on the merits filed and Answer Brief on the Merits Timmie McNeal, defendant and appellant Jamie Popper, counsel
Aug 11 2008	Reply brief filed (case not yet fully briefed) the People, plaintiff and respondent Mark Vos, Dep. D.A.
Sep 12 2008	Reply brief filed (case fully briefed) Timmie McNeal, appellant Jamie Popper, counsel filed with permission
Oct 29 2008	Amicus curiae brief filed California DUI Lawyers Association, David Stanford, Marta Gajewski, Lyle Clayton Turner and Ronald Audia, in support of appellant
Oct 29 2008	Amicus curiae brief filed California District Attorneys Association, in support of respondent
Nov 17 2008	Response to amicus curiae brief filed Timmie McNeal, appellant Jamie Popper, counsel Response to brief of Calif. Dist. Attys Association
Nov 19 2008	Response to amicus curiae brief filed The People, respondent Mark Vos, Dep. D.A. Response to brief of Calif. DUI Lawyers Association (timely-CRC 8.25b)

Brief Downloads
People Opening Brief.pdf (362289 bytes) - People's Opening Brief
Defense Opening and Answer Brief.pdf (371136 bytes) - Defendant's Opening & Answer Brief
People Reply Brief.pdf (309480 bytes) - People's Reply Brief
Defense Reply Brief.pdf (147711 bytes) - Defendant's Reply Brief
Amicus People (CDAA) Brief.pdf (1027839 bytes) - Amicus Brief by CDAA
Amicus Defense (Genis) Brief.pdf (2334020 bytes) - Amicus Brief by Darryl Genis
People Answer to Amicus.pdf (252733 bytes) - People's Answer to Amicus (Genis) Brief
Defense Answer to Amicus (CDAA).pdf (880160 bytes) - Defendant's Answer to Amicus (CDAA)

If you'd like to submit a brief document to be included for this opinion, please submit an e-mail to the SCOCAL website

May 12, 2011 Annotated by Will Edelman

Facts An officer stopped McNeal after seeing him drive through two red lights. McNeal displayed numerous signs of intoxication, and failed each field sobriety test the officer administered. The officer arrested McNeal for DUI and administered a breath test about an hour after the initial stop. McNeal blew into the breath machine five times but produced only two valid samples, both of which registered a blood-alcohol level of 0.10 percent. The government charged McNeal with both “generic” and “per se” DUI under Vehicle Code sections 23152(a) and 23152(b), respectively. At trial, a prosecution expert opined that a person displaying all of McNeal’s signs of impairment was too impaired to drive safely. A defense expert conceded that the scientific community considers a person with a blood-alcohol level over .08 to be under the influence of alcohol, but testified that he considered McNeal’s test results unreliable because the machine’s repeated failure to register sufficient samples suggested it was not working properly. After both sides rested, but before closing arguments, the defense moved to reopen its case to present expert testimony about partition ratio variability in connection with the generic DUI charge. The court denied the motion. In its jury instructions on the generic DUI count, the court included language reflecting the rebuttable presumption in Vehicle Code section 23610(a)(3) that a jury may, but is not required to, infer that a defendant with a blood-alcohol concentration of .08 percent or higher was under the influence. The jury convicted on the generic DUI charge but hung on the per se count. Procedural History McNeal moved for a new trial, arguing that he should have been permitted to introduce the partition ratio evidence to rebut the presumption that he was under the influence of alcohol. When the court denied his motion, he sought review in the appellate division of the superior court. The appellate division held that 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. The Court of Appeal distinguished between evidence about the variability of partition ratios in the general population, and evidence showing that an individual defendant has a nonstandard ratio. It held that only the latter type of evidence—that a particular defendant has a different partition ratio—should be admitted. The Court of Appeal agreed with the appellate division that any error in rejecting McNeal’s proffered evidence was harmless. Both McNeal and the government petitioned for review. The Supreme Court of California granted the petitions. Issue May a defendant charged with “generic DUI” introduce competent evidence about partition ratio variability to rebut section 23610’s presumption of intoxication? Holding Yes, competent evidence about partition ratio variability is relevant and admissible in generic DUI cases to rebut the statutory presumption of intoxication found in Vehicle Code section 23610. The trial court’s error in refusing to admit such evidence in this case was harmless. Analysis Under California law, a defendant accused of driving under the influence can be charged with two separate crimes. The “generic DUI” charge prohibits driving “under the influence” of alcohol, see Vehicle Code § 23152(a), while the “per se” charge prohibits driving with a blood-alcohol level of .08 percent or more, see id. § 23152(b). In generic DUI cases, the government benefits from a statutory presumption that a driver is under the influence if the driver’s blood contains .08 percent or more, by weight, of alcohol in his blood. See id. § 23610. This case concerns how a generic DUI charge can be defended at trial. “Henry’s Law” of chemistry provides that there is a constant ratio between the concentration of alcohol in the blood and the concentration of alcohol in the alveolar air of the lungs. Breath testing machines use a mathematical constant reflecting that ratio to compute a blood-alcohol percentage from a measurement of the amount of alcohol vapor expelled into alveolar spaces deep in the lungs. Breath-testing machines in California use a conversion factor of 2100 to 1. That ratio is used, apparently without exception, in breath-testing devices throughout the United States. Although the 2100-to-1 factor is universal in the machines, actual partition ratios vary—both among members of the population and within a single individual. See People v. Bransford, 8 Cal. 4th 885, 889 (1994). In People v. McDonald, 206 Cal. App. 3d 877, 880 (1988), for example, an expert testified that a person’s ratio could be as high as 2700 to 1 or as low as 1550 to 1. Most experts agree, however, that the 2100-to-1 ratio roughly approximates or even underestimates the ratio of most people. The per se DUI law, enacted in 1981, was the Legislature’s response to concerns that a generic DUI law alone provided too much room for defendants to escape conviction by focusing on a defendant’s subjective behavior and condition. In the years following the enactment of the new per se crime, however, courts permitted defendants to challenge per se DUI charges by using variable partition ratio evidence to raise a reasonable doubt that the state had proved a blood-alcohol level of .08 or more. In 1989, the Legislature responded by amending the law to specify a 2100-to-1 partition ratio for purposes of both the per se DUI offense and the presumption of intoxication for generic DUI charges. The committee reports accompanying that legislative change point to the Legislature’s intent to prohibit defendants in per se cases from challenging breath test results based on the partition ratio. As a result of the amendment, the offense of per se DUI is now defined in terms of a prohibited level of blood alcohol or breath alcohol, and a conversion from breath to blood-alcohol concentration is no longer required to establish guilt. Accordingly, as the Court recognized in Bransford, variable partition ratio evidence is no longer relevant in a per se DUI prosecution. 8 Cal. 4th at 890. But the legislative history is equivocal on the intent of the Legislature when it amended now-section 23610’s presumption of intoxication applicable to generic DUI cases. The question of whether a defendant’s converted blood alcohol level is accurate depends upon the validity of the 2100-to-1 partition ratio. Evidence that a defendant has a comparatively low partition ratio would tend to show that a blood-alcohol concentration calculated with the standard 2100-to-1 ratio overstates the actual amount of alcohol in his blood, which could, in turn, support an inference that he was not under the influence in violation of the generic DUI law. Evidence about the variability of partition ratios in the general population is relevant to raise a reasonable doubt about the accuracy of a defendant’s converted blood-alcohol level. The People, reasoning as the Court did in Bransford, argue that the Legislature rendered partition ratio evidence irrelevant when it amended section 23610 to add the 2100-to-1 partition ratio. But in Bransford, the Court was construing language that defined an offense, while here the language describes a rebuttable presumption—the jury is free to reject the presumption’s inference. The conversion factor, like the rest of the presumption, is rebuttable. Moreover, section 23610 specifically mandates that it “shall not be construed as limiting the introduction of any other competent evidence bearing upon the question of whether the person ingested any alcoholic beverage or was under the influence of an alcoholic beverage at the time of the alleged offense.” See Vehicle Code section 23610(c). The People’s argument that “other competent evidence” excludes partition ratio evidence cannot be reconciled with the plain language of the statute. Competent evidence that the 2100-to-1 ratio does not accurately reflect the partition ratio for all people, or that the defendant’s partition ratio may have been lower, is relevant to whether a chemical test offered as circumstantial evidence to support section 23610’s inference is accurate. The Court of Appeal’s distinction between “general” and “personal” partition ratio evidence does not survive close scrutiny. Both types of evidence challenge the accuracy of the defendant’s reported blood-alcohol level, and therefore support an inference that, despite a high breath test result, the defendant was not under the influence. The inference may be less direct when the evidence is not tied to the defendant, but indirectness alone is not a reason to exclude logically relevant evidence. Partition ratio evidence may not, however, be used to negate the basic fact triggering the section 23610 presumption. Because the section expressly incorporates the 2100-to-1 ratio, the defendant may not argue that the presumption does not apply because a different ratio should have been used. The evidence is relevant to rebut the presumption, but not to remove it altogether. The two other state courts to discuss the admissibility of partition ratio evidence in generic DUI cases agree. See State v. Hanks, 172 Vt. 93, 96 (2001); Guthrie v. Jones, 202 Ariz. 273 (Ct. App. 2002). Because variable partition ratio evidence is admissible to rebut the section 23610 presumption, it is not necessary consider whether a contrary interpretation would raise constitutional concerns. The evidence must still, of course, satisfy standards of competence and all other applicable evidentiary requirements. This opinion does not address how a party might establish partition ratio variability, nor does it consider whether evidence of an individual’s personal partition ratio has gained sufficient acceptance in the scientific community to be admissible. The trial court's error below was harmless. Because the court merely rejected some evidence, but did not preclude the defendant from presenting a defense, harmless error analysis applies. In light of the overwhelming evidence of McNeal’s guilt, it is not reasonably probable he would have achieved a more favorable result absent exclusion of the partition ratio evidence. The jury’s verdict further demonstrates the harmless nature of the error, as nearly half the jury rejected the accuracy of the breath test result and declined to find him guilty of the per se DUI charge. It is difficult to imagine that these same jurors who rejected the breath test result in the per se charge relied on it (and the section 23610 presumption) to convict him on the generic DUI count. Related Authority Vehicle Code § 23152(a)-(b) Vehicle Code § 23610 People v. Bransford, 8 Cal. 4th 885, 889 (1994) State v. Hanks, 172 Vt. 93, 96 (2001) Guthrie v. Jones, 202 Ariz. 273 (Ct. App. 2002) Tags variable partition ratio breathalyzer DUI generic DUI per se DUI driving under the influence conversion factor vehicle code section 23610 vehicle code section 23152(a) rebuttable presumption Annotation by Will Edelman

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