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  • Writer's pictureDavid A. Cmelik Law PLC

DUI Lawyer: Are police misusing PBT?


A preliminary breath test, or, PBT, is a portable device approved by the Iowa public safety commissioner for the purpose of determining whether reasonable grounds exist to invoke implied consent in a drunk driving investigation. In other words, a PBT is one of a battery of field sobriety tests that can contribute to the DUI investigating officer’s grounds to require that the test subject return to the station house to face further, evidentiary DUI chemical testing.

Sometimes DUI-- called OWI in Iowa-- criminal defendants confuse the portable breath test with the desktop breath test because each requires a breath sample. However, the drunk driving PBT test result is inadmissible at trial because state law says it is inadmissible at trial. That’s right, the first breath screen the office takes in the field cannot be shown to the jury in an Iowa prosecution for Operating While Intoxicated, Iowa's criminal DUI statute. The Iowa Supreme Court has held that this is because the device is inherently unreliable. It wrote:

"The problem with this quick, convenient test is unreliability. To guard against this problem, the legislature chose to make the 'results' inadmissible in evidence . . . The unreliability inherent in the test goes to both aspects of the test; not only may the test register an inaccurate numerical percentage of alcohol present in the breath, it may also be inaccurate as to the presence or absence of any alcohol at all." State v. Deshaw, 404 N.W.2d 156, 158 (Iowa 1987)

Because Iowa Code § 321J.5 requires that an officer have “reasonable grounds” to request a PBT breath sample in the field, officers run test subjects through a battery of other so-called standardized field sobriety tests (SFSTs) before the PBT -- like the horizontal gaze nystagmus (HGN), or, eye test, the Walk and Turn, and the One Leg Stand. At this point, some officers may assert that they have enough “reasonable grounds,” and in fact, probable cause to arrest the test subject for OWI. I have never seen a recorded SFST administration where an officer releases a test subject after a PBT refusal. They always arrest the test subject, at least in cases where I am reviewing videos. However, that stands to reason since I'm a criminal defense lawyer. I have also only one time seen an officer merely detain, rather than arrest, an SFST test subject following a PBT. More than once I have seen a defendant arrested without even asking for a PBT. I have in the majority of cases seen officers make an arrest well before the Datamaster DMT administration.

The latter tells me that the PBT is superfluous to law enforcement in a DUI investigation. But it also tells me that officers are over confident in the administration of SFSTs that even the National Highway Traffic Safety Administration recognizes produce false positives in a significant number of test subjects.

If someone exhibits four so-called “clues” on the HGN, 12 out of 100 are below the presumptive level of intoxication and the rest may indicate merely legal prescription drug use or a false positive for position alcohol nystagmus.

The NHTSA acknowledges that 17 out of a 100 test subjects who reach a decision point indicating insobriety on the One Leg Stand are below the presumptive level of intoxication.

To cover for each of these tests flaws, the NHTSA argues that the combined probability is much greater but still acknowledges that nine out of 100 are still sober even if they fail all three SFSTs, or just under ten percent.

Should law enforcement be relying so heavily on SFSTs for so-called “reasonable grounds” to believe the Defendant is intoxicated? In their view, yes. The statute allows law enforcement to conclude they have reasonable grounds even before they administer the PBT—it’s legally required pursuant to Iowa Code § 321J.5, which states, “When a peace officer has reasonable grounds to believe that either of the following have occurred, the peace officer may request that the operator provide a sample of the operator's breath for a preliminary screening test using a device approved by the commissioner of public safety for that purpose.”

But some officers are so confident in their observations and the SFSTs other than the PBT that they will use the PBT simply to determine the nature of the intoxication. In other words, as one officer informed a test subject recently, “this doesn’t tell me whether you are intoxicated, it tells what you used to get intoxicated.” In other words, the officer had already decided the test subject was intoxicated, even before administering the PBT. Query whether this type of foregone conclusion does a disservice to both the full battery of SFSTs—which is intended to include the PBT—as well as the test subject who is never informed that the SFSTs are, by the federal government’s own admission, not reliable enough to rely on individually.


If you or a loved one have been arrested for drunk driving in Iowa, called Operating While Intoxicated, contact us for an initial consultation.

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