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DUI Field Tests

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The intoxication field tests are an important piece of evidence in your case.

The National Highway Transportation Safety Administration has approved three field tests for use in DUI arrests and prosecutions. Despite the fact that the arresting officer nearly always testifies that the defendant “failed” the tests, regardless of the defendant’s performance, an experienced Denver DUI defense lawyer can effectively cross-examine the officer about all three tests.

Horizontal gaze nystagmus

The horizontal gaze nystagmus (HGN) test involves following a specific point, usually a fingertip, small flashlight or ink pen, with your eyes, without moving your head. The theory behind the HGN test is that intoxication causes involuntary eye movements.

One obvious problem with the HGN field test is that it occurs in uncontrolled conditions. Other substances, such as anti-seizure medications, can also cause nystagmus. Finally, even in a controlled environment, and with alcohol as the only possible cause, the HGN test is only 88 percent effective, at the maximum.


In this test, the object is to walk a straight line, heel-to-toe. This is a common method of checking balance and coordination.

The officer should give a woman the option to remove high-heeled shoes. The test should occur on a flat, even surface, and the defendant should walk a real line instead of an imaginary line. Sometimes, all these protocols and other ones are not followed. The walk-and-turn test is even more inaccurate (79 percent maximum) than the HGN test.


The one-leg-stand test also judges coordination, this time by having the defendant stand on one leg for 30 seconds. Continuing a familiar pattern, the test takes place in an uncontrolled environment and is only 83 percent reliable.

The field tests can be refuted in court. Contact The Orr Law Firm for a free consultation with an attorney with effective DUI defense strategies.