If you are arrested for DUI and the police legally take a sample of your breath or blood, you can be convicted if the test result shows a blood alcohol concentration of at least 0.08%. Under California’s “per se” law, no other evidence is necessary to obtain a DUI conviction.
There is no “per se” law for cocaine in California. Some states make it illegal to drive with any detectable amount of cocaine in the driver’s blood, but California has not followed that trend.
A blood test can confirm that you used cocaine, but no specific amount of cocaine in the blood is sufficient to prove that a driver was “under the influence.” In fact, research sponsored by the National Highway Traffic Safety Administration (NHTSA) concluded that there is no consensus among toxicologists about the quantity of most drugs (including cocaine) that is likely to impair the ability to drive.
Driving “under the influence” of cocaine means the driver’s physical or mental abilities have been impaired to a degree that makes the driver incapable of driving as cautiously as a sober person. Impairment is often obvious after a driver consumes a large quantity of alcohol, but cocaine tends to increase a driver’s alertness while alcohol tends to muddy the mind. That fact makes alcohol-related DUI easier to prove than cocaine DUI, even in the absence of chemical test results.
While unsafe driving is not itself sufficient to prove that a driver was under the influence of cocaine, it is a factor that a jury can consider when it decides whether the prosecutor proved cocaine DUI beyond a reasonable doubt. Prosecutors often rely on a combination of unsafe driving, poor performance on field sobriety tests, and blood test results showing the presence of cocaine to prove a cocaine DUI charge. Fortunately for accused drivers, that evidence is nearly always ambiguous.
Careful cross-examination (or recordings made by dashboard cameras in police cars) often reveals that claims of unsafe driving are overstated. For example, what a police officer will characterize as “swerving” often turns out to be a slow drift within a traffic lane.
In addition, there is usually an innocent explanation for unsafe driving behavior. A driver may have swerved or deviated from a traffic lane to avoid an obstacle in the road. The driver may have taken his or her eyes off the road momentarily to study a GPS display. Innocent explanations of arguably unsafe driving can undercut the prosecution’s claim that the driver was under the influence of cocaine.
According to NHTSA, field sobriety tests (FSTs) have been validated for alcohol consumption, not for cocaine consumption. Of the three standardized FSTs, NHTSA gives the most weight to the horizontal gaze nystagmus (HGN) test. An officer conducting an HGN test looks for nystagmus (twitching) in the eyes while they follow a moving object. Whatever relevance the HGN might have to proof of alcohol impairment, NHTSA admits that cocaine does not cause nystagmus.
The two remaining field sobriety tests address a driver’s ability to maintain balance and remember instructions. No scientific research establishes that those tests (walking in a straight line and standing on one leg) can establish physical or mental impairment due to cocaine use. A skilled cross-examination and the application of common sense often convinces juries that poor performance on FSTs proves nothing.
Since it is difficult to find evidence that justifies an arrest for cocaine DUI, much less a conviction, prosecutors sometimes rely on a Drug Recognition Expert (DRE). A DRE is usually a police officer who has completed a “training” program that supposedly qualifies the officer to decide that a driver is under the influence of drugs. The DRE is usually called to the scene of a traffic stop to assess whether a driver should be arrested for DUI after the driver’s preliminary breath test for alcohol returns a result of zero. The DRE will then testify for the prosecution at the driver’s trial.
An aggressive cross-examination of drug recognition experts invariably reveals that they have been trained to help prosecutors get convictions, not to make rational judgments based on a sound application of scientific principles. When DRE witnesses are asked to elaborate on the “science” that supports their conclusions, they typically falter. They can never explain why the same test results would establish that someone is under the influence of cocaine, a stimulant that enhances sensory perception, and Xanax, a depressant that dulls it. Since the testimony of DRE witnesses is based on pseudoscience, it is not surprising that they cannot withstand cross-examination.