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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.  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.
The first type of roadside test, 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.  Motorists often 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.  And, now the unwitting motorist has provided additional evidence for the government to use against him or her.
The second type of test is the roadside evidential test.  There is a 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.  Implied consent is a required in having a license to drive.  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).
The situation is 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.  Many DUI / DWI criminal defense lawyers advise people to refuse all roadside breath tests to avoid confusion and insist upon a blood test if they are ever suspected of drunk driving.
The same test becomes mandatory once the driver is arrested, triggering the “implied consent” law.  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 in exchange for the privilege of driving. It is utmost importance to keep the distinction in mind between the two types of cases because, if you refuse to take a chemical test after arrest, the police can note a “refusal”, which can have significant ramifications.  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).
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.
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 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 limitations of the technology of the machine.  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. 
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.
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 based on 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.
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.

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