Driving Under the Influence Tests: What to Expect

Driving under the influence (DUI) tests are measures used to detect whether the driver of a vehicle has been consuming drugs or alcohol. One way that police officers will try to gauge whether a driver is under the influence is to perform “Field Sobriety Tests” (FSTs). These tests can be used in a court of law as evidence of a defendant’s intoxication while driving. FSTs generally measure balance, coordination and response time, which tends to be impaired in a person who has been drinking. One example of an FST is the horizontal gaze nystagmus test, in which the driver is asked to focus their eyes on an object, usually a pen, while the officer moves it from side to side. This test allows the officer to observe any abnormal shaking or jerking movements in the driver’s eyes while the object is being moved.

In addition to FSTs, officers may utilize a breathalyzer test. Breathalyzer tests are portable devices that can measure a person’s blood alcohol content (BAC) when he or she blows into the machine. Though these tests are usually accurate, it is common for attorneys to argue cause for error when defending a client charged with a DUI. A defendant may also request to review the police departments’ breathalyzer test maintenance logs to verify whether the machines have been receiving proper upkeep.

A more accurate measure of a driver’s BAC is a blood test. If the driver of a vehicle refuses to submit to a breathalyzer test or FSTs, this will likely result in his or her arrest and a forced blood draw will be ordered. Although blood draws are more expensive, they are also more accurate.
Urine tests, though used more for testing a longer-term presence of drugs, can also be used to test a person’s BAC. For a urine test the driver would need to be taken to a facility to provide a urine sample that could be tested for chemicals. These tests are accurate, and they can be used to show that a person has been driving under the influence.

Lastly, saliva tests can be used to detect both drugs and alcohol in drivers suspected of DUI. A saliva test involves using a swab to obtain a saliva sample from inside the driver’s mouth. These tests are not as popular as breathalyzers, but they are gaining in popularity.

Sources discussing DUI tests:
http://www.duifoundation.org/drunkdriving/testing/fieldsobriety/