Assessing Sobriety / Intoxication

A number of formal studies have found it quite difficult to judge mild and moderate levels of intoxication in people who are strangers. A major problem is the enormous differences among people in their response to alcohol - and to a lesser degree, differences in the same person depending on circumstances. Some people may feel significantly impaired at legal blood alcohol concentrations ( BAC) well below the legal standard (.08%), whereas other people (typically chronic alcoholics) may show no noticeable impairment (even when examined by physicians in emergency rooms) at BAC levels of .30% and even .40%.

When a driver is stopped by a police officer, especially late at night, the officer will observe for sign of alcohol consumption and impairment. The National Highway Transportation and Safety Administration (NHTSA) lists a number of potential clues, including rumpled clothing, odor of alcohol, red or glassy eyes, poor coordination, and loud or slurred speech.

Researchers have also examined indications of intoxication in an attempt to make more accurate judgments. Several general conclusions can be drawn: While individual clues (e.g., red eyes, slurred speech) occur at different BACs on the average, there is wide individual variation, and 2) some people (probably chronic alcoholics) do not show the expected clues.

The difficulty in judging intoxication, combined with the high number of alcohol-related traffic fatalities, led NHTSA to develop a set of standardized sobriety tests. These were introduced in the mid 1980's and consisted of three tests: Horizontal Gaze Nystagmus (HGN), Walk and Turn, and One Leg Stand. HGN involves assessing the driver's eyes for jerkiness (nystagmus) when following a moving object or when held to the side. All three tests are standardized and should be administered, scored, and interpreted the same way each time. Often, however, they are not. This is one major defense in DWI / DUI cases.

However, even if they are conducted correctly, there are many limitations to the tests is determining if someone is intoxicated. A partial listing includes:

• Lack of norms for how sober people of different ages perform
• Use of BAC, rather than some index of impairment, as a criterion
• Limited investigation of the effects of fatigue, anxiety or fear on performance
• No research on how performance on the tests relates to driving impairment
• Considerable variability between different officers in administration and scoring of the tests
• Failure to report data, including unflattering false positive rates

While all these factors are important, the last factor in particular will lead police officers and prosecutors to overvalue the tests. NHTSA training materials do clearly report false positive rates, and claim that medical conditions that may lead to false arrests are rare, particularly among people that drive. No data or citations are given for this important claim.

FSA certification indicates that your police officer, prosecutor, defense attorney, and judge understands field sobriety testing from a scientific perspective, not just the NHTSA/police science perspective. While NHTSA training helps all parties comprehend the limitations of the evidence when the officer makes major mistakes performing the SFSTs, it provides little assistance when they don't. Rather, NHTSA appears to promote the field sobriety tests as more accurate than justified by the scientific evidence of their validity (see Judge Grimm's analysis in US v. Horn, 185 F.Supp.2d 530 (D.Md. 2002).