If a North Carolina police officer suspects that a motorist is driving while intoxicated or driving under the influence (DWI/DUI), they'll generally have them perform a standard field sobriety test (SFST). These tests are 90% accurate when performed correctly. There are three primary components of the SFST.
One of the first factors tested as part of the SFST is the motorist's horizontal gaze nystagmus (HGN). A motorist who was DWI/DUI will generally have trouble tracking moving objects when asked to follow them with their eyes. They often experience an involuntary jerking of their eyeballs at reduced angles as they refocus their gaze from one side to another.
Another component of the SFST is the walk-and-turn test. Motorists will generally be asked by a police officer to take nine heel-to-heel steps in one direction in a straight line. They'll then be asked to walk back to them. If the motorist has trouble placing one foot in front of another, turning, taking too many steps, failing to walk in a straight line or uses their arms to balance, then this may indicate that they were DWI/DUI.
The final component of the SFST is the one-leg stand test. During this exercise, a motorist suspected of DWI/DUI is generally asked to hold one of their legs at least six inches up in the air for up to 30 seconds. If a motorist uses their arms to steady oneself, hops or sways to maintain balance or simply puts their foot down, then these may indicate to the officer that they are DWI/DUI.
A motorist who fails one part of the SFST isn't automatically considered to have DWI/DUI. They may have had a valid reason such as an illness, injury or disability that resulted in them having done so. This is why officers complete three different tests. It's important that an officer asks the motorists about any potential reason for their failure of them and notes it in their report.
While SFSTs are largely accurate at identifying individuals who are DWI/DUI, that's only the case if they're performed correctly. While they are admissible as evidence in a court of law, a defendant can produce their documentation showing that health and other factors led them to perform poorly on these tests.
A DWI/DUI attorney can advise you of different defense strategies that can be pursued in your Statesville case if you've been charged with a crime.