Jones Law | DUI & Criminal Defense | Fresno, CA


10 Dec

What are Drunk Driving Tests: Field Sobriety Tests; Breath Tests; and Blood Tests?

Posted by David Jones on Dec 10, 2013


A key part of the defense representation that a DUI defense lawyer will provide to a client facing drunk driving charges is the challenging of all tests used by law enforcement to determine whether a driver is "under the influence" of alcohol or drugs. There are two key types of tests to consider: field sobriety tests and chemical tests.

Field Sobriety Tests (FSTs) are used to determine whether a driver's mental and/or physical abilities are impaired by alcohol or a controlled substance.

Chemical Tests, usually either a breathalyzer or blood test, are used to determine whether a driver has a blood alcohol concentration of .08% or greater (above the legal limit to operate a motor vehicle in California).


Field sobriety tests take place before a drunk driving arrests. These are preliminary tests that law enforcement officers can ask a person to submit to if they have been lawfully pulled over in a traffic stop or at a legal DUI checkpoint. There are four basic types of field sobriety tests, and law enforcement can use one or a combination of any of these tests. One is the horizontal gaze nystagmus, in which the officer will track a suspect's eye movements with an object such as a pen. The one-leg stand test requires a suspect to stand on one leg without that foot touching the ground and without excessive wobbling. The walk-and-turn test requires a suspect to walk in a straight line, turn around and walk back the same way. Finally, the preliminary alcohol screening device (PAS), commonly used in California, is a portable breath test machine.


Chemical tests can only be required after a lawful arrest. There are three types of chemical tests that can measure blood alcohol concentration (BAC) and those are the breath, blood and urine tests. These tests are either administered by licensed law enforcement officials or by other licensed professionals. For a standard DUI stop, an officer will typically choose a breath test. Blood and urine tests are more common in DUIs involving drugs or extreme DUI cases.

Failure to take a chemical test after arrest can result in automatic driver's license suspension.

While chemical tests over .08 percent BAC can result in license suspension and a DUI charge, this does not necessarily mean that you are guilty. You are still innocent and have the right to an attorney to contest your suspension and charges at the DMV hearing and court hearings.


When you work with Jones Law, you can count on our experience and resources as we assist you with addressing the drunk driving tests that pertain to your case. We can challenge DUI evidence from every angle, looking at the manner in which your breath test or blood test was administered or even challenging an alleged test refusal. We can also handle cases that involve tests administered at or following a DUI checkpoint.

Because we understand the ins and outs of drunk driving testing procedures, we can recognize deviations from standard procedure, mistakes by law enforcements or other ways that an arresting officer may "cut corners" in an attempt to make an arrest for driving under the influence. Make no mistake, your attorney's knowledge and experience in regard to these tests may have a significant impact on the outcome of your case. It may be the smallest of details that turns the case in your favor.

David Jones


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