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How Does an HGN Test Affect My Chances of a DWI Conviction?

If a law enforcement officer suspects you of drunk driving, you will likely be subjected to a number of tests. In addition to the well-known Breathalyzer, the officer will also likely administer one or more field sobriety tests, including the horizontal gaze nystagmus (HGN) test. This is where the officer waves a small object in front of you from side-to-side–about 12-15 inches from your nose–and asks you to follow it the with your eyes, without you moving your head. In this scenario the officer is looking for six “clues” suggesting intoxication, three in each eye. The presence of four of the six clues is generally considered sufficient “probable cause” to charge you with DWI.

Appeals Court Finds Any Potential Mistake in HGN Test a “Harmless Error”

Even in cases where the police officer may incorrectly administer an HGN test, however, there may still be sufficient evidence of DWI to convict you at trial. This recently came up in a Houston DWI case, York v. State. Early one morning in March 2016, a Houston Police Department officer the defendant driving his pickup truck erratically. Specifically, the defendant moved “across four lanes of traffic without using a turn signal and then fail to maintain a single lane,” according to the officer.“

The officer initiated a traffic stop. After smelling a “strong odor of alcohol” and observing the defendant had “red and glassy” eyes, the officer decided to administer three field sobriety tests, including the HGN Test. With respect to the HGN test, the officer observed all six of the clues. Based on the defendant’s overall performance on the tests, he was arrested and charged with DWI. After his arrest, a DWI technician at the police department administered the field sobriety tests to the defendant a second time. On the HGN test, the technician observed all six clues, just as the arresting officer did. The technician also administered a breath-alcohol test, which indicated the defendant’s blood-alcohol concentration was 0.113 percent, well over the legal limit of .08 percent.

A jury convicted the defendant of misdemeanor DWI. The trial judge sentenced the defendant to 180 days in jail, but suspended that sentence in favor of one year of community supervision (probation). The defendant still appealed his conviction. One of his arguments on appeal was that the DWI technician improperly administered the second HGN test, and therefore the trial judge erred in allowing the jury to hear the technician’s testimony on this point. The Court of Appeals rejected this argument. It held the technician did not administer the test incorrectly–but even if he did, that did not affect the defendant’s “substantial right” to a fair trial. The Court noted the prosecution did not “dwell on or emphasize” the HGN test results to the jury, which heard plenty of other evidence regarding the defendant’s intoxication, including the officer’s initial HGN test.

Get Help from a Galveston or League City DWI Defense Lawyer Today

As you can see from this case, a drunk driving arrest is often not based on a single test or piece of evidence. Houston-area law enforcement is well-trained to identify multiple possible signs of intoxication. This is why you need to work with an experienced Houston DWI defense attorney if you are facing criminal charges. Contact the Law Offices of Tad Nelson & Associates online or call us at (281) 280-0100 if you need help with a DWI or drunk driving case today.