Big Changes Coming For California Dui Cases

The July 2009 California Supreme Court's decision in People v McNeal can potentially be one of the most important DUI/DWI defense cases that an attorney has in his or her DUI/DWI defense arsenal.

According to McNeal, defendants who have been charged with a generic DUI (sometimes referred to as "general impairment" DUI) may now bring evidence of their individual partition ratios to contest the accuracy of the breath alcohol content test results. Prior to this decision, defendants were not permitted to challenge the formula used to convert a breath alcohol reading taken by a breath testing instrument into a blood alcohol content reading.

Generic DUIs and Per Se DUIs

Generally, when a driver is arrested on suspicion of driving under the influence (DUI), the driver will be charged with two separate offenses:

  • Generic DUI (Vehicle Code §23152(a))
  • Per se DUI (Vehicle Code §23152(b))

In order to prove a driver is guilty of a generic DUI, the prosecution must prove that the driver was impaired at the time he or she was operating a vehicle. State law creates a presumption that a driver is intoxicated if he or she has a blood alcohol content of at least 0.08 (Vehicle Code §23610).

A driver is guilty of a per se DUI if the driver has a blood alcohol content of 0.08 or higher. This can be proven by either showing that the driver had the prohibited level of alcohol in 100 milliliters of blood or in 210 liters of breath. The prosecution does not have to prove the driver was in fact impaired - simply having the requisite blood or breath alcohol content is enough to prove guilt.

Standard Partition Ratios

Police commonly use breath testing instruments to determine a driver's blood alcohol content, especially at the roadside following a DUI stop of the driver. Since these devices measure the amount of alcohol in the driver's breath rather than the blood, the machines must convert the measurement to determine the amount of alcohol present in the driver's blood. This conversion is known as the "standard partition ratio."

In California (and the majority of other states), the standard partition ratio is set at 2100:1. This means that every 2100 milliliters of alcohol present in the breath is equivalent to 1 milliliter of alcohol present in the blood.

The reliability of the standard partition ratio has been widely attacked. It has been scientifically proven and accepted by courts that the partition ratio is not the same for all people and that the partition ratio for any one individual can vary greatly at different times of the day. It is estimated that 30% of the population has a partition ratio different than 2100:1. Some of the factors that can impact a partition ratio include the person's sex, body temperature, medical conditions and the amount of time between consuming the alcohol and taking the alcohol content reading.

Even so, the majority of scientists still believe that using a 2100:1 ratio is acceptable because it represents or is lower than the ratio of most people. In fact, it is believed that the majority of the population has a 2300:1 ratio. This means that the majority of people will receive lower blood alcohol content readings than they actually may have when the conversion is done.

People v McNeal

In People v McNeal, the defendant was charged with a per se DUI and a generic DUI after being arrested by the police for running two red stoplights and exhibiting other signs of intoxication. An hour after the arrest, the defendant took a breathalyzer test, which registered his BAC at 0.10. The defendant was convicted by the Superior Court in San Bernardino County after his defense attorney unsuccessfully tried to introduce evidence challenging the standard partition ratio used to convert the defendant's breath test results into a blood alcohol content reading.

On appeal, the appellate court upheld the lower court's ruling. However, the California Supreme Court agreed to hear the case and ultimately upheld the trial court's ruling on procedural grounds. The state's highest court ruled that defendants in DUI cases have the right to bring competent evidence challenging the validity of the standard partition ratio in regards to a generic DUI charge.

This means that defendants may now bring evidence to challenge the accuracy of the conversion ratio of 2100:1. A defendant may present evidence of his or her own partition ratio, or he or she may simply present evidence of the variance in partition ratios among the public.

Although this evidence may not be used to defend against a per se DUI violation (because the statute is written in such a way that a conversion from breath content results into blood content results is not necessary) the jury will still hear this evidence at the trial - which may subconsciously affect their ultimate decision upon the defendant's innocence or guilt.

Questions Remaining After McNeal

While the McNeal opinion is a victory for those facing generic DUI charges, the court's opinion left several questions unanswered.

For example, the court declined to provide guidance as to how a defendant could establish his or her own partition ratio. The court also stated that it had "no opinion" on the question of whether evidence of an individual's own partition ratio would even be admissible in court. Generally for scientific evidence to be admissible, the scientific principles the evidence relies on must have gained general acceptance in the particular scientific field. However, there currently are no established procedures for determining a person's partition ratio.

This seems to create a paradoxical situation, in which defendants have the right to introduce evidence, but that evidence may be inadmissible because there currently is no accepted scientific procedure for collecting it.

Given the uncertainty of how the McNeal decision ultimately will affect the outcome of DUI cases in California, it is important than anyone facing a drunk driving charge work with an attorney experienced in defending these charges. In addition to attacking the standard partition ratio, there are other means to challenge a DUI charge. An experienced DUI attorney can discuss these options with you.