PA Court Overturns DUI Conviction After Judge Denies Defense Expert Witness Testimony

Posted in DUI on June 29, 2025

The Pennsylvania Superior Court recently vacated a York County woman’s convictions for Driving Under the Influence (DUI) and Endangering the Welfare of a Child (EWOC) after ruling that the trial court improperly excluded expert testimony that could have helped her defense. This case serves as a crucial reminder that, even in DUI and drug-related cases, defendants have the right to present expert witnesses to challenge the Commonwealth’s evidence.

If you’re facing DUI, drug, or child endangerment charges in State College or Centre County, it’s essential to have an aggressive and knowledgeable criminal defense attorney on your side to ensure your rights are protected.

Case Background — Commonwealth v. Taylor

Taylor was arrested after crashing her vehicle into a utility pole with her 18-month-old child in the car. Police alleged that Taylor was impaired by drugs at the time of the crash, pointing to her slurred speech, bloodshot eyes, and poor performance on field sobriety tests. She admitted to taking prescribed Adderall and Xanax but denied any impairment.

Taylor was charged with:

✅ Driving Under the Influence of a Controlled Substance (DUI – Drugs)
✅ Endangering the Welfare of a Child (EWOC)

At trial, the prosecution relied heavily on the arresting officer’s observations and the results of the field sobriety tests, claiming they indicated drug impairment.

Expert Witness Excluded at Trial

Taylor’s defense team sought to present testimony from Dr. Lawrence Guzzardi, a medical toxicologist, who would have explained that field sobriety tests are only scientifically validated for detecting alcohol impairment — not drug impairment. However, the trial court refused to allow this testimony, ruling that Dr. Guzzardi lacked the practical experience to critique field sobriety testing.

The jury found Taylor guilty on both charges, and she received a sentence that included jail time and house arrest.

Pennsylvania Superior Court: Trial Court Got It Wrong

On appeal, the Superior Court ruled that excluding Dr. Guzzardi’s testimony was a legal error. The Court emphasized that:

✔ Expert witnesses do not need hands-on experience administering field sobriety tests to testify about their scientific validity.
✔ Dr. Guzzardi’s years of scholarly research and medical expertise qualified him to opine on whether field sobriety tests are reliable indicators of drug impairment.
✔ Excluding his testimony unfairly prevented the jury from hearing critical evidence that could have cast doubt on the Commonwealth’s case.

The Court concluded that this error was not “harmless” and could have contributed to the guilty verdict. As a result, Taylor’s convictions were vacated, and a new trial was ordered.

Why This Matters for State College DUI and Drug Defense

This case is a powerful reminder that:

✅ Field sobriety tests have limitations, especially when it comes to alleged drug impairment.
✅ Police observations are not always reliable, and expert witnesses can be critical to challenging faulty evidence.
✅ Judges sometimes make mistakes that can severely impact the fairness of a trial.

If you’ve been arrested for DUI – Drugs, marijuana DUI, prescription drug DUI, or child endangerment in Pennsylvania, it’s critical to have a defense lawyer who understands how to challenge every aspect of the prosecution’s case, including:

Protect Your Rights — Call a State College DUI Defense Lawyer

At JD Law, we aggressively defend clients facing DUI, drug charges, and child endangerment throughout State College, Centre County, and surrounding areas. We know how to challenge improper evidence, fight for the inclusion of expert testimony, and protect your rights at every stage of the process.

For a free case review, contact JD Law by email or leave a message at (814) 689-9139. Email is the preferred method of communication, as phone calls are directed to voicemail due to the high volume of spam and unsolicited calls.