During a traffic stop, law enforcement may want evaluate a driver to determine if they are impaired by drugs or alcohol. Post-arrest, the police will request the driver take a breath test and if it reads 0.08% BAC or higher, then they’ll be charged with a DUI. A urine test for drugs may be requested after a negative breath alcohol result.
However, police are also trained to have a suspected drunk driver perform physical evaluations called standardized field sobriety tests (SFST) to establish probable cause for arrest. There are three kinds of SFSTs (validated by NHTSA- The National Highway Traffic Safety Administration) that you should recognize, which include:
1. Horizontal gaze nystagmus test (HGN)
A horizontal gaze nystagmus test evaluates several things: a driver’s focus on an object, smoothness of tracking a moving object, and the presence of an involuntary jerking of the eye. The officer will ask the driver to look at a single spot and, without moving their head, follow it with their eyes.
2. Walk-and-turn test (WAT)
The officer may ask the driver to walk heel-to toe on straight line and walk back to where they started following a walk-and-turn test. The officer is likely evaluating the driver’s ability to stay balanced or follow instructions. If the driver stumbles or struggles to walk on the line, the officer can use that result an an indication of impairment.
3. One-legged stand test (OLS)
The driver may be asked to perform a one-legged stand test. This test, as the name implies, has a driver stand on one leg. Like the walk-and-turn test, the police are likely watching to see if the driver puts their foot down over or is unable to follow directions.
4. Non-standardized field sobriety tests (NSFST)
You should also understand that the police may also perform non-standardized field sobriety tests. An NSFST may involve saying the alphabet backward while doing jumping jacks or having a driver stretch out their arms and put their finger on their nose.
You should understand their legal rights during a traffic stop, like how drivers shouldn’t face punishment by refusing an SFST or NSFST. Learn more about roadside sobriety exercises here.