The NHTSA has approved three standardized field sobriety tests in the New Jersey: the HGN (horizontal gaze nystagmus), the walk and turn and the one leg stand. New Jersey police officers are trained on how to conduct each test if they suspect someone of drinking and driving.

The HGN Test

Thought of as the most reliable of the three, this test has a 77% to 88% reliability if the test is administered properly. It is also the only test that is deemed “scientific”. It is supposed to work this way:

The police officer will ask you to hold your head still and follow an object such as a pen or light with your eyes. The officer will look for nystagmus, which is an involuntary jerking of the eyes brought on by alcohol consumption. The problem is that many people suffer from nystagmus naturally.

The officer will look for three clues in each eye for a total of six clues. If the officer notices four clues, you have failed the HGN.

The Walk and Turn

Unlike the HGN, this is a divided attention test. You’ll be tested on your physical performance and also your ability to follow instructions. The officer MUST explain the test and also demonstrate it for you.

You’ll be told to walk a line (sometimes it’s imaginary!) and take nine heel-to-toe steps. You’ll pivot off your front foot and walk back in the same manner all the while counting out loud. If the officer notices you can’t stay balanced, you don’t take the right number of steps or count out loud, or you step off the line, this counts against you. If the officer observes two clues, this a fail.

The One Leg Stand

This is divided attention test number two. Here the officer will ask you to raise one foot six inches off the ground. You’ll be told to count out loud until you’re told to stop. You must look down, point your toe out and keep your arms at your sides during the test.

If you stop the test early, put your foot down, forget to count out loud or use your arms for balance, this counts against you. Once the officer notices two of these clues, you can be arrested for DUI.

One of the most controversial aspects of a DWI/DUI stop by a police officer is the Field Sobriety Tests (FSTs). The National Highway Traffic Safety Administration (NHTSA) has developed a model system for managing Standardized Field Sobriety Test (SFST) training. They have published numerous training manuals associated with FSTs. NHTSA have conducted numerous studies to validate the Standard FSTs. FSTs are heavily subject to the opinion of the arresting officer. Many sober people are unable to perform the tests properly with a false positive rate of 23% and some are even arrested for failing the tests. The walk-and-turn test is only 68% accurate, and the one-leg stand test is only 65% accurate in healthy individuals, when determining if a person is under the influence. People with medical conditions, injuries, 65 years or older, and 50 pounds or greater overweight cannot be accurately judged by these tests. The officer will administer one or more field sobriety tests (FSTs). FSTs are "divided attention tests" that theoretically test the suspect's ability to perform the type of mental and physical multitasking that is required to operate an automobile. However, these tests can be problematic for people with nonobvious disabilities affecting proprioception, such as Ehlers-Danlos syndrome. The most commonly administered FSTs include:

• horizontal gaze nystagmus test, which involves following an object with the eyes (such as a pen) to determine characteristic eye movement reaction.
• walk-and-turn (heel-to-toe in a straight line). (This test is designed to measure a person's ability to follow directions and remember a series of steps while dividing attention between physical and mental tasks.)
• one-leg-stand.
• modified-position-of-attention (feet together, head back, eyes closed for thirty seconds; also known as the Romberg test).
• finger-to-nose (tip head back, eyes closed, touch the tip of nose with tip of index finger).
• recite all or part of the alphabet (As of 08/2010, reciting the alphabet backwards is required in an FST in Amherst, Massachusetts.)
• (finger count) touch each finger of hand to thumb counting with each touch (1, 2, 3, 4, 4, 3, 2, 1).
• count backwards from a number such as 30 or 100.
• breathe into a "portable or preliminary breath tester" or PBT.

Although most law enforcement agencies continue to use a variety of these FSTs, increasingly a 3-test battery of standardized field sobriety tests (SFSTs) is being adopted. These tests are recommended by the National Highway Traffic Safety Administration (NHTSA) after studies indicated other FSTs were relatively unreliable. The NHTSA-approved battery of tests consists of the horizontal gaze nystagmus test, the walk-and-turn test, and the one-leg-stand. In some states, such as Ohio, only the standardized tests will be admitted into evidence, provided they were administered and objectively scored "in substantial compliance" with NHTSA standards (ORC 4511.19(D)(4)(b)).

FSTs are more effective at determining the level of impairment than they are at estimating the driver's blood alcohol concentration (BAC). However, studies throw doubt on the tests' usefulness in helping an officer to judge either. In 1991, Dr. Spurgeon Cole of Clemson University conducted a study of the accuracy of FSTs. His staff videotaped people performing six common field sobriety tests, then showed the tapes to 14 police officers and asked them to decide whether the suspects had "had too much to drink and drive" (sic). The blood-alcohol concentration of each of the 21 DUI subjects was 0.00, unknown to the officers. The result: the officers gave their opinion that 46% of these innocent people were too drunk to be able to drive. This study showed the possible inaccuracy of FSTs.

An increasingly used field sobriety test involves having the suspect breathe into a small, handheld breath testing device. Called variously a PAS ("preliminary alcohol screening") or PBT ("preliminary breath test"), the units are small, inexpensive versions of the larger, more sophisticated instruments at the police stations, the EBTs ("evidentiary breath test"). Whereas the EBTs usually employ infrared spectroscopy, the PAS units use a relatively simple electrochemical (fuel cell) technology. Their purpose, along with other FSTs, is to assist the officer in determining probable cause for arrest. Although, because of their relative inaccuracy, they were never intended to be used in court for proving actual blood-alcohol concentration, some courts have begun to admit them as evidence of BAC.