Rule 702(a1) was enacted in 2006 (effective for hearings held August 21, 2006 or later) to render admissible two types of expert testimony on the issue of impairment: (1) testimony regarding the results of a Horizontal Gaze Nystagmus (HGN) test; and (2) testimony from a certified Drug Recognition Expert (DRE) regarding whether a person is under the influence of an impairing substance. For both types of expert testimony, the rule specifies that testimony is admissible solely on the issue of impairment and not on the issue of a specific alcohol concentration level. Expertise in HGN and drug recognition and classification are premised upon standardized curricula developed by the National Highway Transportation Safety Administration. HGN is one of three components of the Standardized Field Sobriety Test battery. The others are the Walk-and-Turn and the One-Leg Stand tests. The latter tests measure behavior that a lay person without specialized training would commonly associate with intoxication such as lack of balance and coordination. The HGN test, in contrast, evaluates the eye’s ability to smoothly follow a moving stimulus and the jerking of the eye (termed “nystagmus”) as it moves to the far side of a person’s vision. Specialized, or scientific, knowledge is required to correlate this type of eye movement with intoxication. Thus, before enactment of Rule 702(a1)(1), the state supreme court held in State v. Helms, 348 N.C. 578 (1998), that testimony from a police officer regarding the results of an HGN test performed by the defendant was inadmissible without the introduction [...]
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