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 vehicle in a manner like that of an ordinarily prudent and
cautious person in full possession of his faculties. 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. The
ultimate question was defined in terms of the defendant's subjective behavior
and condition. 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. 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). Thus, after 1981 there
were two parallel statutes making it a crime to drive while intoxicated.
Generic DUI and "Per Se DUI." People v. McNeal, 46 Cal.4th
at 1192-1193.
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. 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 (f).)1 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.
McNeal, 46 Cal.4th at 1194. 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."2
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. 4318.3 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. 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. People v. McNeal, 46 Cal.4th at 1195-1196.
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