Contact us today to learn how our firm can help you win your case.

HGN Expert Testimony in North Carolina DWI Trials

Expert testimony, as I described in my previous post on this issue, is admissible under a hybrid rule in North Carolina articulated in Goode, Howerton, and related cases such as Ward. That three-part test is used for most expert testimony and, until 2006, for the Horizontal Gaze Nystagmus test (HGN) used in many DWI prosecutions.

In State v. Helms, 345 NC 578 (1998), the Supreme Court held that the HGN test should be subjected to the same test as in Goode. The state, before offering the evidence in a DWI trial, should show that the foundational requirements of HGN reliability and the officer’s training in the field.

While not an incredibly high burden to meet, that still put the onus on the State to make sure it could show that HGN is actually reliable. There is a lot of peer reviewed scientific literature showing that HGN is not a reliable indicator of impairment. (see Rubenzer) for an overview of scholarly research on HGN.)

But HGN (and DRE) are relatively cost effective ways for the State to try to prove impairment. The HGN “certification” only requires the officer to attend a 24 hour SFST course, which at most costs the State a couple hundred dollars including the NHTSA Student Manual. After that brief course, the officer can go into the field and conduct hundreds of HGN tests on suspected drunk drivers.

Consequently, the Governor’s task force on DWI lobbied the legislature to amend North Carolina’s Rules of Evidence in 2006 to allow the HGN to be admitted into evidence by partially bypassing the test established in Goode and Helms. See also Shea Denning’s article on the School of Government website.

NCRE 702 (a1) reads:

A witness, qualified under subsection (a) of this section and with proper foundation, may give expert testimony solely on the issue of impairment and not on the issue of specific alcohol concentration level relating to the following:

(1) The results of a Horizontal Gaze Nystagmus (HGN) Test when the test is administered by a person who has successfully completed training in HGN.

Anyone who shows they have successfully completed training in HGN can testify. Having completed the training in HGN, I can testify in a DWI trial as an expert. And, believe me, I, like almost all officers, fall far short of an opthamologist’s training.

However, Rule 702 has an initial requirement that the scientific, technical, or other specialized knowledge assist the trier of fact to understand the evidence or determine a fact in issue. If that prong is not satisfied, either because the person’s “expert” testimony is not very learned or deep, or because the person lacked the opportunity to observe HGN because of improper application of the test, then the testimony is not admissible.

This issue is often overlooked by DWI lawyers who assume that because HGN has been declared a forensic science by the legislature and because a person holding a certificate can testify, that there is no way to challenge the admissibility of HGN.

One option available to an attorney challenging the admissibility of the HGN testimony is to take the witness on voir dire where the attorney challenging the admissibility of the testimony can ask questions about how the test was performed and whether the witness has sufficient understanding of HGN to explain to the trier of fact what the presence of HGN means.

Incidentally, even though I tend to think HGN is mostly junk science, officers I respect swear by it. When those officers come to the stand and have a very good understanding of the mechanics of HGN and the underlying science, it makes for interesting testimony and for a good trial where issues can be hashed out.



* All Fields Required


(919) 352-9411

office hours
  • Monday 8am-8pm

  • Tuesday 8am-8pm

  • Wednesday 8am-8pm

  • Thursday 8am-8pm

  • Friday 8am-8pm

  • Sat & Sun 8am-8pm




  • * All Fields Required