Overview of Methods for Roadside Sobriety Testing in DUIs

Written by Maya Fouad

When a police officer is conducting a roadside investigation of a suspected drunk driver, a variety of mechanisms are employed as indicators of intoxication.  Law enforcement are trained to conduct specific behavioral tests and use certain devices designed to detect levels of intoxication.  Officers are often additionally trained to make more general observations of the suspect during roadside investigations of this nature.  For instance, the potential odor of alcohol, an individual’s flushed face, or the appearance of the eyes, can all also be additional indicators of intoxication; however, few evidentiary limits apply when an officer with personal knowledge testifies to such observations.  In contrast, evidence of intoxication resulting from officers performing more established methods of testing implicate more potential grounds for exclusion.  

Since 1981, the National Highway Traffic Safety Admission (NHTSA) of the United States Department of Transportation has produced a series of standardized field sobriety tests which are considered the most effective procedures for testing drivers at roadside for intoxication.  The NHSTA’s behavioral test battery has been incorporated into law enforcement training in all states to help police officers in assessing whether a suspected drunk driver is legally impaired.  The tests are administered roadside, outside of the car, and after the suspected drunk driver has been identified.  The SFST battery is composed of three tests: the Horizontal Gaze Nystagmus (HGN), the Walk-and-Turn (WAT), and the One-Leg Stand (OLS).  Since 1995, the Georgia Peace Officer Standards and Training Council has made the three NHSTA-approved field tests the exclusive field tests taught to Georgia officers.

Horizontal Gaze Nystagmus (HGN).  The HGN test is a simple eye test designed to detect nystagmus, or involuntary jerking of the eyes which is attributable to the ingestion of alcohol.  Many individuals exhibit some nystagmus (or jerking) of the eyes as they are turned as far as possible to the side; however, as people become intoxicated, the onset of the jerking occurs sooner and becomes more distinct.  The HGN test developed by the NHTSA uses the following three measures for officers to gauge intoxication: (1) the angle of onset, or how soon the nystagmus occurs as eyes move to the side; (2) the maximum deviation, or how distinct the nystagmus appears as eyes are as far to the side as possible; and (3) smooth pursuit, or whether the driver is able to follow a slow moving object smoothly with their eyes.  Studies by the NHTSA suggest that of all three SFSTs, the HGN test is the most reliable indicator of intoxication.

In an HGN examination, the suspected intoxicated driver stands with both feet together and arms at their side, then they must follow the movement of a stimulus with their eyes.  The officer examines the angle of onset, maximum deviation, and smooth pursuit.  One point is scored on each of these factors for each eye, for a possible total of six points.  Four or more points on an HGN examination is taken to indicate an individual’s blood-alcohol concentration is over 0.10 percent.  HGN tests are commonly used as the initial inquiry into a driver’s level of intoxication.

Walk-and-Turn (WAT).  The WAT and OLS tests are both used to observe the effect of alcohol on an individual’s balance.  In a WAT test, the suspected drunk driver is required to stand heel-to-toe while listening to instructions about the test from the officer.  Specifically, the subject is instructed to take nine heel-to-toe steps down a straight line, turn around by pivoting on one foot, then take nine heel-to-toe steps back.  The WAT test is based on research showing that alcohol impairs one’s ability to complete divided attention tasks, or concentrate on two things at once.  If the subject remains balanced but needs to have the instructions repeated, or if the subject understands the instructions but loses balance, then they are deemed to have failed the WAT test.  Failure indicates a BAC at or above 0.10 percent.

One-Leg Stand (OLS).  The OLS test gauges intoxication of a suspected drunk driver through testing the individual’s balance in another divided attention task.  In an OLS test, the subject is asked to stand with their heels together and is then instructed to raise one leg six inches off the ground.  While holding that position, the subject is asked to count rapidly from 1001 to 1030.  If the individual either loses balance, or is unable to properly count the numbers, they are deemed to have failed the OLS test.  Again, failure indicates a BAC at or above 0.10 percent.

Preliminary Breath Testers (PBTs). While not categorized as an SFST, preliminary breath testers are screening devices commonly used by law enforcement to detect the presence or absence of alcohol on the breath of a suspected drunk driver.  These commercially available breath-testing instruments are often used in conjunction with the behavioral SFSTs discussed above as a basis for arresting a subject for further testing.  PBTs refer to AlcoSensors, breathalyzers, Taguchi Gas Sensors, et cetera. A number of devices have been developed and approved for use by law enforcement; however, PBTs generally operate the same by using chemical reactions from the alcohol vapor on an individual’s breath to determine a value for the BAC.  In Georgia, the AlcoSensor sold by Intoximeters, Inc. has been traditionally used by officers in determining whether a motorist is under the influence of alcohol.  The Georgia Bureau of Investigation has additionally approved the use of two other PBTs (the A.L.E.R.T. device and the Alcolyzer); however, the AlcoSensor remains the most used in preliminary field testing.  Like most PBTs, the AlcoSensor employs fuel cell technology, which measures alcohol oxidation that occurs when a breath sample interacts with an acidic electrolyte solution. 

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