Many DUI / DWI arrests involve roadside breath tests, which are designed to measure a driver’s blood alcohol content (BAC). Although prosecutors point to Preliminary Alcohol Screening (PAS) test results as damning evidence in drunk driving cases, in truth these tests are far from ironclad, and can often be successfully challenged in court. An experienced California criminal defense attorney who specializes in DUI / DUI cases knows how to challenge PAS tests in a drunk driving case.
The central factor in a Driving Under the Influence arrest and subsequent drunk driving prosecution is the motorist’s alcohol level at the time of driving, not at the police station, where many BAC tests are performed. Stationhouse breath or blood test results are only relevant to the extent that they allow someone to look back in time, and draw inferences about the motorist’s blood or breath alcohol level at the earlier time of driving. This is done through what is known as “retrograde extrapolation,” where a forensic alcohol expert reviews known (or supposed) drinking patterns, eating patterns, and various times of these events, to arrive at an opinion of BAC at the time of driving.
There are many problems with this type of calculation. The only way for retrograde extrapolation to pass scientific muster is for certain assumptions to be made. The first, and most critical, is that the motorist be in the “post-absorptive” or “elimination” phase. Without making this assumption, the prosecution’s forensic expert cannot engage in the scientific speculation necessary to reach their desired conclusion.
Additionally, as more and more time passes from the time of drinking to the time of driving to the time of testing, the BAC at the time of driving becomes increasingly hard to accurately pinpoint. Thus, in an attempt to develop evidence closer in time to the time of driving, roadside breath testing has gained popularity.
DUI / DWI criminal defense attorneys have been dealing with roadside breath testing for years. In the early days of roadside breath testing for alcohol, it was readily acknowledged that the technology was somewhat inferior, and that roadside PAS tests were not reliable enough to be admitted into evidence. Therefore, when an officer used an alcohol screening test as part of a drinking and driving investigation, the only thing that could be introduced in evidence at a DUI / DWI trial would be that the PAS machine indicated the presence of alcohol. The numeric results were excluded at any drunk driving trial.
Unfortunately, that is no longer the case. In recent years, courts hearing DUI / DWI trials have allowed in the numeric results of the PAS tests to be considered by the jury, so long as certain evidentiary foundations were established. As a result, motorists targeted for drunk driving roadside investigations are taking roadside breath tests after being advised that their participation is entirely voluntary, only to have the numeric results introduced at trial.
There are two types of roadside breath tests that are given: PAS or PBT tests, which are merely screening tests given to support the officer’s decision to make an arrest, and roadside evidential tests. There are critical distinctions between the two.
It’s important to note that the PAS test is a voluntary test. PAS stands for Preliminary Alcohol Screening. It is not an “implied consent” test, which means that there is no requirement that the motorist take this test as there is with the post-arrest breath test. In fact, in many states, the officer performing the roadside DUI / DWI investigation is required to advise the driver that he is requesting the test to better assist the officer in determining whether the motorist is under the influence of alcohol. The officer must advise the driver that he or she is under no obligation to take the test, but if an arrest is made, the driver will then be required to submit to a test of his or her blood or breath to determine alcohol content.
Unfortunately, it appears that many officers ignore this responsibility when conducting a DUI / DWI roadside investigation. Many times, motorists report that the officer indicates quite forcefully that he or she must submit to a test, then the collection tube is thrust into the mouth of the awestruck motorist. A drunk driving arrest invariably follows. It likely would have followed anyway, except now the unwitting motorist has provided additional evidence for the government to use against him or her.
Roadside DUI / DWI investigations are made still more complex because of the recent addition of the Evidential PAS test, also known as the “E-PAS” or AlcoSensor IV XL, to the drunk driving detection arsenal. These versions of the roadside breath test are the evidential test that is required under the implied consent laws. These mandatory tests are given on the exact same machine that was, moments earlier before the driver was arrested, an optional test. The only difference is that now, in a post-arrest setting, they are able to print out the results (as compared to a screening test, where the results are merely displayed on an LED readout).
This is even further complicated by the fact that the motorist is often unclear as to the moment that they are placed under arrest for drinking and driving. One minute they are offered a roadside test, and told it is optional. The next, they are told that a roadside breath alcohol test on the same machine is mandatory. It is obvious that confusion can result. This is why many DUI / DWI criminal defense lawyers advise people to refuse all roadside breath tests and insist upon a blood test if they are ever the target of a drunk driving investigation.
However, once arrested, the “implied consent” law is triggered. The implied consent law is that every driver has impliedly consented to a test of their blood or breath to determine alcohol content following a DUI / DWI arrest. The failure to give this blood or breath sample following a drunk driving arrest can result in administrative sanctions from the Department of Motor Vehicles (DMV) which begin at a one-year driver’s license suspension (with no opportunity for a restricted or provisional license during that year).
Roadside breath testing arose to address a significant issue in DUI / DWI prosecution – because of the typical time lapse between driving and testing, there was often an issue of whether the motorist’s alcohol level could have been below the legal limit at the time of driving, and then rose to a level that exceeded the legal limit at the time of testing. The aim of roadside breath testing in drunk driving cases was to eliminate that issue by fixing the blood or breath alcohol level (BAC) at a time closer to the time of driving.
While the goal of achieving greater scientific certainty may have been a good one, in practice, there are significant problems in these drinking and driving arrests that overshadow any advances made. The challenges to both the PAS test (the pre-arrest roadside breath test in DUI / DWI investigations) and the E-PAS (the post-arrest roadside breath test) are the same, as the PAS and E-PAS machines are the same. The distinction is that the E-PAS is hooked up to a printer, providing the DUI / DWI arrestee a copy of the printout of the faulty device.
DUI / DWI prosecutions are, in many respects, just like any other criminal case. In order for prosecutors to get a conviction, they must prove each element of their case beyond a reasonable doubt, to the exclusion of every reasonable doubt. If the prosecutor is unable to present a case that is 100 percent free of reasonable doubt, the driver cannot be convicted. This notion is at the heart of every criminal case, whether it is driving under the influence of alcohol, DUI drugs, vehicular manslaughter, robbery, murder, or any other.
Therefore, before the results of the breath test can be trusted to prove a motorist’s guilt beyond a reasonable doubt, there are evidentiary foundations that must be observed. Thus, the first challenge against these machines relates to their calibration, maintenance and accuracy. Both field breath testing units and stationhouse breath testing units are subject to problems with calibration, maintenance, and accuracy, and it is vital to explore these issues in every drunk driving prosecution.
It is also important to probe to determine whether the officer that administered the breath test was properly trained to do so. There are rules and regulations regarding the administration of breath tests, and it is fundamental that only those who have gone through appropriate training should be performing these tests on motorists suspected of driving under the influence of alcohol.
One of the most important challenges to the roadside tests in a DUI / DWI arrests relates to the technology of the machine itself. The roadside PAS devices are all “fuel cell” machines. In short, alcohol is oxidized on an electromagnetic plate, and the amount of electrochemical energy generated is converted to a number that is supposedly equal to the blood-alcohol level of the motorist.
Several problems are invited by this technology, including the possibility that other compounds in the human breath being misinterpreted as alcohol, problems related to a buildup that creates falsely high results, and, most importantly, the lack of a mouth alcohol detector.
Mouth alcohol is one of the biggest challenges in forensic breath testing. The danger of mouth alcohol contamination is at the heart of much of the rules and regulations in breath testing, such as a 15- or 20-minute waiting period, observing the subject to ensure they do not regurgitate or introduce foreign material in the mouth, the requirement of giving two samples that are in agreement with each other. These are all critical issues in DUI / DWI cases, and especially in cases involving the PAS machine.
This is because the PAS machine does NOT have a mouth alcohol detector, also called a slope detector. A mouth alcohol detector is really a computer software program that is designed to detect a rapid drop-off (or slope) in the alcohol level of an individual breath sample. The machine is not smart enough to know whether it is analyzing alcohol molecules in the deep lung air – what it is supposed to be measuring – or alcohol molecules that have been trapped in the mouth or regurgitated from the stomach. This is especially problematic where a motorist is given a breath test shortly after drinking, while alcohol is still in the stomach, or has been trapped in the mouth due to dental work or food traps.
Yet another challenge with the PAS test is that it does not measure breath temperature. All of the calculations that it does are based on the assumption that the subject’s breath temperature is 34 degrees centigrade. Unfortunately, just like the other assumptions that are made which relate to the so-called “average” person, any variation from “average” can greatly impact the reading. Every degree of temperature elevation – which could be from illness, dancing, or engaging in sports activities – equals a 7 percent increase in alcohol percentage.
It is also worth mentioning that many motorists who find themselves as the target of a drunk driving investigation are simply improper subjects for breath testing. DUI / DWI criminal defense lawyers are aware that those who have had recent dental work, or who suffer from GERD (gastro esophageal reflux disorder, the technical name for persistent heartburn) are inappropriate subjects for breath testing. There are many other conditions that could cause an unnaturally high reading on a breath test.
It is therefore vital anyone arrested for a DUI / DWI, drunk driving, or any drinking and driving offense, contact a criminal defense attorney who is well-versed in these issues. The results of the roadside breath test are often the most damning evidence offered in a DUI / DWI case. It is essential that these results be challenged to achieve a successful result.