Using Gammill to Strike Police Officers as Experts in Civil Cases Involving Commercial Vehicle Collisions

Police officers—especially uniformed state troopers—are often designated as expert witnesses in civil cases involving motor vehicle collisions. Their testimony can carry immense weight with jurors, who view law enforcement officers as trustworthy public servants. However, courts must not allow that trust to substitute for the legal requirements of reliability, foundation, and relevance.

The Texas Supreme Court has made clear through Gammill v. Jack Williams Chevrolet, Inc. and E.I. du Pont de Nemours v. Robinson that expert testimony must meet rigorous reliability standards under Rule 702 of the Texas Rules of Evidence—regardless of who offers it.

The “Expert Halo” and the Gatekeeping Role of the Court

Once someone is labeled an expert, juries often defer to their opinions. When that person wears a badge and uniform, the perceived credibility only increases. But courts have repeatedly emphasized that expert witnesses cannot rely on their authority alone. Instead, they must:

• Demonstrate expertise in the specific area,
• Use sound methodology,
• Show how they connected facts to conclusions.

In Gammill, the court warned against “ipse dixit” opinions—those based only on the expert’s say-so.

Trooper Testimony Must Be Scrutinized

In one recent case, a DPS Trooper named Robert McGrath was designated as an expert in a multi-vehicle commercial truck collision. Our clients had undergone several surgeries and had significant medical damages. Trooper McGrath, however, decided to place the entirety of the blame on a single vehicle with minimum limits. Our job was to dispute and distinguish Trooper McGrath’s accident reconstruction and crash report, to financially provide for our clients.

Upon closer examination, McGrath’s deposition testimony revealed significant deficiencies.

Lack of Methodology and Data Connection

• McGrath failed to interview key eyewitnesses who contradicted his findings.
• He speculated the plaintiff was on a phone during the crash—with no supporting evidence.
• He criticized vehicle speeds but admitted he could not calculate proper stopping distances.
• He interpreted 18-wheeler ECM data despite acknowledging no training in doing so.

Inadequate Qualifications and Experience

• McGrath admitted he was not an expert in 18-wheelers, biomechanics, human factors, or federal trucking regulations.
• He had only worked on three commercial vehicle collisions prior to this case.
• He had never testified in a civil trial.

Errors and Contradictions

• He misidentified tire marks as yaw marks and used incorrect formulas.
• He failed to measure critical evidence and destroyed investigative photographs.
• He contradicted his own scale diagram during deposition.
• His math was incorrect and his conclusions were impossible to verify.

Legal Tools to Exclude Police Expert Testimony

To successfully strike a police officer as an expert:

1. Cite Texas Case Law: Use Gammill, Robinson, TXI Transportation, and Burrow v. Arce to show the requirements for expert reliability.
2. Depose Thoroughly: Lock the officer into his or her qualifications, opinions, and methodologies.
3. Expose Gaps: Demonstrate a lack of data, math errors, contradictions, and failure to follow accepted accident reconstruction methods.
4. Contrast with Competent Experts: Show the difference between the officer’s approach and that of a trained, professional reconstructionist.

Conclusion

The courtroom must be a place of facts, not assumptions. Courts should not hesitate to exclude expert opinions from police officers who fail to meet the standards of Rule 702. As Gammill and Robinson make clear, the uniform does not carry an evidentiary presumption of reliability.

Don’t be scared of a bad crash report. That is only the first step in evaluating the case. If the damages are severe enough, there is always a way to get around it.

All expert testimony—whether from a professor, a doctor, or a police officer—must rest on demonstrable facts, sound methodology, and a clear connection between the two. Otherwise, it has no place in front of a jury.