Prior to the FSTs, many officers make some accommodations. They normally do not require people with prosthetic legs to perform the one-leg stand test and they sometimes give women the chance to take off high-heel shoes prior to the walk-and-turn test. If officers deny needed accommodations, the test results are skewed.
The Horizontal Gaze Nystagmus test is one of the three NHTSA-approved field sobriety tests. In almost all DWI cases, the FST results constitute probable cause for the arrest. If the defendant refuses to provide a breath or blood sample, the prosecutor must also use the FST results to establish intoxication beyond a reasonable doubt at trial.
At first blush, the one-leg stand test may seem like a rather mindless exercise. The ability to stand on one leg for fifteen or so seconds may seem unrelated to the ability to drive a car.
A hard-core fan blamed his team's ineptitude for a serious injury DWI crash outside the Meadowlands in New Jersey.
In most DWI defense matters, intoxication is the only issue. The state can use either direct or circumstantial evidence to prove intoxication. A chemical test that shows a BAC above the legal limit is proof of intoxication as a matter of law. Or, the prosecutor can rely on the circumstantial evidence from the field sobriety tests.
Today's Breathalyzer is based on the Drunk-O-Meter, which appeared in the 1930s. So, the Breathalyzer is a very well-established piece of technology. However, the Breathalyzer has also not changed very much since those early models. Thus, the flaws inherent in those early models still remain today.
Pretty much every voter in the Lone Star State knows that Robert "Beto" O'Rourke was arrested for DWI in El Paso in 1998. His arrest, and the subsequent disposition, show how much DWI laws have changed in Texas over the last twenty years.
Breathalyzers make up the vast majority of DWI chemical tests in Texas. Since the Supreme Court ruled that blood tests require search warrants, that will probably remain true for quite some time. Occasionally, Texas law enforcement agencies hold "no-refusal weekends." If drivers refuse Breathalyzer tests, officers will obtain search warrants for blood tests. So, you can refuse a chemical test, and that refusal is effective until they strap you onto a gurney and stick a needle in your arm.