The California Supreme Court ruled this week that scientific evidence that challenges the accuracy of breath testing measures for DUI cases is not admissible evidence in court. This comes after a recent case where a California man, Terry Vangelder, attempted to fight his charge by bringing in an expert witness who questioned the accuracy of Breathalyzer tests in general. Vangelder was arrested in 2007 for suspicion of DUI he passed his field sobriety tests, but blew a .086% on the breathalyzer test. He was later given a chemical breath test which registered at .08% and a blood test that showed a blood-alcohol concentration of 0.87%.
At his trial in front of the Supreme Court, Vangelder produced professional witness Dr. Michael P. Hlastala who is a professor of medicine at the University of Washington. Dr. Hlastala testified that breath testing devices do not give scientifically accurate results of DUI.
The professor explained that the machine reading can change based on the speed and depth of breathing, body and breath temperature, and the ratio of red blood cells to total blood volume. These factors could lead to the reading either overstating or understating the true alcohol content of the blood.
In their ruling, the California Supreme Court said that challenging the use of breath tests' ability to determine sobriety is not a valid legal defense. California Vehicle Code section 23153(b) states that anyone with a blood alcohol concentration over .08% is considered intoxicated. Lawmakers have already decided that breath test results count as a valid way to measure sobriety.
The only way for a DUI suspect to fight their breath test results is to argue that the machine used to take the measurement malfunctioned, was not calibrated properly or was administered incorrectly. The court also stated that scientific evidence could be used to challenge a general DUI charge but not a per se DUI charge where the defendant was found to be impaired because they had a BAC over the legal limit.