Once a driver has made been subjected to the first two stages of a DUI investigation, the initial stop and the personal contact phases, the officer will need to decide based on that evidence whether the matter should be escalated to the third and final phase of the DWI investigation: the pre-arrest stage.

If there is sufficient evidence of intoxication, then the officer will continue his or her investigation to try and determine the extent of the driver’s impairment. This is primarily done through the use of breath tests and field sobriety tests. These two tools allow officers relatively quick and reasonably accurate ways of assessing whether a driver is too impaired to safely operate a motor vehicle. So what are the signs of intoxication that officers look for during this stage?

Though there are a range of activities an officer could ask a suspected drunk driver to perform, the National Highway Traffic Safety Administration says that only three tests have been proven to serve as reliable indicators of a driver’s level of legal impairment. These three tests include the one-leg-stand test, the (HGN) or horizontal gaze nystagmus test and the heel-to-toe walk.

The one-leg-stand test is exactly what it sounds like and involves the suspected drunk driver balancing on one leg for around 30 seconds. The test is supposed to reveal whether a driver is impaired, because sober drivers ought to be able to perform the test without trouble. Officers administering this test look for things like swaying, tripping or reaching out for balance as indications of impairment. While this may be true, physical limitations or even simple carelessness might also explain a poor performance.

The second standard field sobriety test is the horizontal gaze nystagmus test (HGN). During the HGN test a driver is asked to follow an object, usually the officer’s finger, back and forth across the person’s field of vision. Research has shown that drunk drivers exhibit a telltale wobble in their eyes when following objects, which is what the officers are watching for. The wobble is reflexive and not within the control of the driver so there are no tips or advice to avoiding it.

Finally, the heel-to-toe walk is another standard component of a field sobriety test and involves the suspected drunk driver walking back and forth in a straight line. In addition to the walk, officers often also throw in additional requests, such as a certain number of steps or seconds, something they use to check your attention to detail. The officer performing the test will watch for a lack of balance, swaying or failure to perform the test as requested as indications of impairment.

Source: “Police Identify Drunk Drivers through Signs of Impairment,” by, published at OhioBar.org.