When a law enforcement officer suspects that a motorist is under the influence of alcohol or drugs, the officer may conduct several tests to confirm that suspicion. Typically, a motorist suspected of intoxicated driving will be asked to submit to a field sobriety test, which is often followed by a breathalyzer, blood, or urine test. Many of us presume that these tests are reasonably accurate, but is that a safe assumption to make?

If a field sobriety test is not administered properly, even the most sober driver can have a tough time passing. The most common field sobriety test is the HGN (horizontal gaze nystagmus) test. If you are given the HGN test, a police officer will ask you to look at a tiny object, usually a pen or a pencil, and follow the object’s movement with your eyes. As you look at the object, the officer looks for involuntary eye movements.

Alcohol reduces the brain’s ability to control the eye muscles, which in turn makes the eyes jerk or “bounce.” The HGN test can indicate intoxication, but it might also indicate that the driver may be taking prescription medications for seizures or may suffer a neurological or visual problem. That’s why HGN tests can be inaccurate and untrustworthy.

Other field sobriety tests attempt to gauge a motorist’s coordination, balance, and cognition. An officer might ask someone to stand on one leg, walk a straight line, or recite letters or numbers. These exercises may indicate – but cannot prove – that a driver is intoxicated.

ARE BREATHALYZER DEVICES ACCURATE?

Breathalyzers are the devices most commonly used by police officers to measure a driver’s blood-alcohol content (or “BAC”) level. The truth is that over the years, breathalyzers have been notoriously unreliable. They must be routinely maintained and calibrated. Several years ago, sixty-nine DUI convictions in Massachusetts came under review when authorities discovered that the breathalyzers used to win those convictions had not been calibrated properly.

Another problem is that breathalyzers cannot distinguish alcohol from substances that have a similar molecular structure. One man in Washington State drank a small amount of gasoline, and a breathalyzer measured his BAC level at almost four times the legal limit, yet the man was sober – there is no alcohol in gasoline.

A person suffering from gastroesophageal reflux disease (GERD) has alcohol gas constantly moving from the stomach to the mouth, so when he or she blows into a breathalyzer device, gas from the stomach mixes with gas from the lungs, and the result is a higher – and inaccurate – BAC level measurement.

Even factors like a driver’s breathing pattern or additional compounds in the blood (usually medications) can affect a breathalyzer result. Some breathalyzer models are vulnerable to radio frequency interference that could lead to inaccurate test results, and radio frequency interference is everywhere. Its sources include virtually all radios, walkie-talkies, cell phones, and radar devices.

ARE BLOOD AND URINE TESTS ACCURATE?

The most accurate test for alcohol or drugs in the body is the blood sample. However, a good Texas DWI attorney can often find problems with the accuracy of blood tests. Most labs that work with blood and/or urine samples run scores of tests and procedures every day, so mistakes are not uncommon. Blood that isn’t stored or properly preserved will give a false reading, and if a laboratory doesn’t follow proper testing and storage procedures, blood samples can be mixed or otherwise contaminated.

Despite these problems, drivers who test above the legal limit for alcohol will very likely face a DWI conviction in Texas. It’s important to understand that being over the “legal” limit is not a requirement for a DWI charge or conviction in this state.

Having probable cause that a driver is intoxicated is enough for a police officer to make an arrest. Testing for drugs other than alcohol – marijuana, for example – is even more complicated and more prone to inaccuracy.

In the state of Texas, any amount of marijuana – even a trace – in a driver’s blood or urine while driving legally establishes that the driver was “under the influence” of marijuana. It’s a controversial law because the active ingredient in marijuana – tetrahydrocannabinol or “THC” – remains in the blood for days and even weeks after a marijuana high has faded, so a blood test for THC cannot “really” prove intoxicated driving. Almost anyone who has used cannabis in the last thirty days or so – and then drives in Texas – could conceivably be convicted of marijuana-DWI.

WHAT IS THE DWI LAW IN TEXAS – AND WHAT ARE THE PENALTIES?

In Texas, a driver age 21 or older who is legally intoxicated or impaired by drugs can be charged and prosecuted for DWI. Drivers under age 21 with any measurable blood alcohol content level will be charged with DUI – whether or not they are impaired. Additionally, Texas drivers under age 21 who are over the legal limit (a BAC level at or above 0.08 percent) may also be prosecuted for DWI.

For a first DWI conviction in Texas, the penalties may include from three to one-hundred-eighty days in jail, a fine of up to $2,000, up to one-hundred hours of community service, a driver’s license suspension for up to a year, and an annual driver’s license fee for three years.

When a driver under age 21 is convicted of DUI, the penalties may include a fine of up to $500, a sixty-day driver’s license suspension, up to forty hours of community service, and court-ordered alcohol education classes.

Texas prosecutors in DUI and DWI cases usually rely on a driver’s field sobriety tests, the chemical testing results, and the arresting officer’s testimony. Field sobriety tests are always suspect, and chemical tests are frequently unreliable. An experienced Dallas DWI attorney can evaluate the charge, review the evidence, and often find a reason for the charge to be reduced or dismissed.

That’s why it’s imperative for any Texas driver charged with DUI or DWI to have high-quality legal representation. A good Dallas DWI attorney will explain a client’s rights, options, and what to expect. Even in the worst scenario – when the evidence is conclusive and a conviction is certain – a diligent DWI lawyer will try to arrange a plea bargain or work for reduced or alternative sentencing. Even with today’s technology, chemical testing for DWI remains relatively unreliable, which means that every Texas driver accused of DWI should obtain legal counsel and contest the charge.