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The HGN is scientifically valid in Illinois DUI prosecutions

A much-anticipated Illinois Supreme Court opinion held that the HGN, one of three standardized field sobriety tests in Illinois DUI cases, was a valid indicator of alcohol impaired driving. What this means in practical terms that the state will not have to provide expert testimony that the HGN is some evidence of alcohol impairment every time it wishes to use the HGN in an Illinois DUI prosecution.

While this decision is helpful to the state, the Supreme Court placed limits on its use. First of all, the state cannot present the test as proof of intoxication. It will be treated like the other standardized field sobriety tests, or like an open beer can in your car, or an odor of alcohol on your breath, or your admission that you had been drinking. None of these things, standing alone, proves that you are drunk. They just tend to make it more likely that you had consumed alcohol.

The Court also held that any police officer who administers the HGN must be trained according to the student manual of the National Traffic Safety Highway Administration (NHTSA).


Before this important decision, many police agencies provided only basic training on administering the HGN. Now, they must be trained according to the manual. Furthermore, they must administer the HGN in accordance with the NHTSA standards.

The Supreme Court recognized that the HGN could suggest impairment even though the driver was below the legal limit of .08. The Court also acknowledged that there are at least 125 causes, other than alcohol, for HGN. In short, even though the test is admissible as evidence in an Illinois DUI prosecution, the Supreme Court has left the door open to many attacks on its reliability.

Newspapers reporting this Illinois DUI decision headline it as a victory for the state. Here is one more reminder of the adage, don’t believe everything you read in the newspaper. If people obtained competent legal advice instead of accepting the ill-informed “advice” of co-workers, friends, relatives and neighbors, they would fare better.

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