According to the Centers for Disease Control and Prevention (CDC), 9,967 people were killed in alcohol-related traffic collisions in 2014. That’s nearly a third of all traffic deaths in the United States. More than a million drivers in the U.S. were arrested in 2014 for driving under the influence of alcohol or drugs. Courts, lawmakers, and police agencies, it seems, are perennially “cracking down” on drunk driving, establishing “task forces,” and passing new laws that never seem to keep the most genuinely dangerous drivers off the street.

Typically, in all fifty states, if a law enforcement officer stops a driver in traffic for any legal reason, and the officer has a reasonable belief reason that the driver has been operating under the influence of drugs or alcohol, the officer will first want to administer a field sobriety test (FST) or a series of field sobriety tests. If the driver’s response and performance tend to confirm the officer’s suspicions, a breath test is usually next.

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Frankly, the FSTs used by California police officers can be tough to pass even for a sober, healthy driver, especially if the test is not properly conducted. The most popular FST with California police officers seems to be the Horizontal Gaze Nystagmus (HGN) test. Alcohol temporarily reduces the brain’s capacity to control the eye muscles, so it causes the eye to uncontrollably bounce or jerk. The officer slowly moves a pen, small flashlight, or even a finger horizontally back and forth to test for the eye movements that are signs of impairment.

WHAT SHOULD A FIELD SOBRIETY TEST TELL A POLICE OFFICER?

Other FSTs are designed to test a driver’s coordination, reflexes, balance, and thinking abilities. A driver may be asked to walk in a straight line, stand on one leg, or recite the alphabet. More than a dozen FSTs are used by police departments across the country. When administered properly, a field sobriety test is supposed to tell a police officer if you should be arrested for suspicion of DUI. However, FSTs are rarely administered properly, and most law enforcement officers have already decided to arrest you by the time they ask you to submit to the FST.

A law enforcement officer may also ask a driver to take a preliminary alcohol screening (PAS) test using a hand-held breathalyzer. In the state of California, drivers over age 21 may decline to take PAS and field sobriety tests unless a driver is on probation for a previous DUI conviction. Like the FSTs, the PAS test is often inaccurate. Most drivers over 21 may decline to take any of these tests before an arrest takes place.

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But when you are arrested for DUI – whether or not you’ve been tested – most states have what is called an “implied consent” law that will automatically come into effect. Implied consent means that merely by driving in a state, a driver has already consented by implication to taking a chemical DUI test if the driver is arrested for suspicion of DUI. Refusing to take a blood, breath, or urine test after being arrested for DUI usually triggers a driver’s license suspension. In California, that driver’s license suspension is for a full year.

WHAT DUI TEST TENDS TO BE THE MOST ACCURATE?

The results of FSTs and chemical DUI tests can determine if a driver is arrested, charged, or convicted for driving under the influence. How accurate are “chemical” DUI tests – the blood, breath, and urine tests that are used as evidence against thousands of drivers? The most accurate test is a blood test, but if a blood sample isn’t properly handled and preserved, or if it becomes contaminated, it can give a false reading.

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In California DUI cases, if the laboratory conducting the blood testing hasn’t followed proper procedures, a good Orange County DUI lawyer can cast doubt on blood test evidence or even move to have it thrown out by the court. However, California drivers should know that in most driving under the influence cases, blood test results are considered “accurate enough” and are usually persuasive.

The “legal limit” for drivers in all fifty states is a “blood alcohol content” or BAC level of 0.08 percent. While breathalyzer devices are said to measure a driver’s blood alcohol content level, the truth is that breathalyzers do not measure the blood at all. Instead, a breathalyzer device indirectly measures a driver’s BAC level based on alcohol in the driver’s breath rather than the blood.

WHY ARE BREATHALYZERS FREQUENTLY INACCURATE?

Breathalyzers can be inaccurate for a number of reasons. Alcohol and related chemicals that a breathalyzer device “reads” as alcohol can be found in a variety of foods, medicines, toothpastes, mouthwashes, and breath fresheners. Breathalyzer devices will return inaccurate results for drivers with medical conditions including gastroesophageal reflux disease (GERD), diabetes, and hypoglycemia.

Breathalyzers are also frequently subject to mechanical malfunctions. A breathalyzer device must be routinely maintained and calibrated, and even then, some breathalyzers are vulnerable to radio frequency interference (RFI), which is in the air whenever police officers are using their radios and walkie-talkies. Police officers must be properly trained in the use of breathalyzers and must conduct breathalyzer exams legally and according to procedures.

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Urine tests have been less accurate than either blood tests or breathalyzer tests for measuring a driver’s level of intoxication. The current law enforcement trend is to administer a urine test to a DUI suspect only if blood and breath tests are unavailable. Urine can remain in the bladder for a considerable length of time, so a urine test is not genuinely indicative of a driver’s “current” blood alcohol content level. And because urine sample analysis is analogous to blood sample analysis, urine sample results are also subject to laboratory contamination and mistakes.

The truth is that in most cases a DUI test will in fact give law enforcement officers a more-or-less accurate measurement of a driver’s BAC level, but the tests are not reliable – and when someone’s freedom and future are at stake, guilt of driving under the influence or any other crime must be proven beyond any reasonable doubt. A “high” rate of accuracy for DUI tests is not good enough. In a southern California DUI trial, an experienced Orange County DUI lawyer might be able to cast enough doubt on borderline test results to persuade a jury that the state has failed to prove its case beyond a reasonable doubt.