What defenses are there in a drunk driving case?
The most common defenses to drunk driving attack either the act of driving itself or the way in which a crucial piece of evidence was obtained. If you were charged with a DUI/DWI, but the prosecutor can’t prove that you were actually driving, then the case may fail on that ground alone. A defense can succeed if the officer lacked probable cause to stop you, or if proper Miranda warning were not given at the time you made an incriminating statement. Blood alcohol tests can run into all sorts of trouble and an experienced DUI/DWI attorney can launch a successful defense pointing out the unreliability of these tests and the way they are administered.
There are a number of potential defenses that can be raised in a given drunk driving case. Roughly speaking, however, the majority of drunk driving defenses can be broken down into the following areas:
(1) "He wasn’t driving": In this defense, intoxication is not enough -- the prosecution must also prove that the defendant was actually driving. This may be difficult if, as in the case of accidents, there are no witnesses to you being the driver of the vehicle. Most drivers quickly admit they were driving, although they had the right to remain silent.
(2) Probable cause: In a drunk driving case, evidence will be suppressed if the officer did not have legal cause to stop, detain, and arrest. In many DUI cases, DUI checkpoints present particularly complex issues.
(3) Miranda rights: Incriminating statements may be suppressed if Miranda warnings were not given at the appropriate time.
(4) Implied consent warnings: If the officer did not advise you of the consequences of refusing to take a chemical test, or gave it incorrectly, this may affect admissibility of the test results -- as well as the license suspension imposed by the Motor Vehicle Department in your state.
(5) "Under the influence": The officer's observations and opinions as to intoxication can be questioned -- the circumstances under which the field sobriety tests were given, for example, or the subjective (and predisposed) nature of what the officer considers as "failing." In drunk driving cases, witnesses can also testify that you appeared to be sober.
(6) Blood-alcohol content (BAC): There exists a wide range of potential problems with blood, breath, or urine testing. "Non-specific" analysis, for example: most breath machines will register many chemical compounds found on the human breath as alcohol. And breath machines assume a 2100-to-1 ratio in converting alcohol in the breath into alcohol in the blood; in fact, this ratio varies widely from person to person (and within a person from one moment to another). Radio frequency interference can result in inaccurate readings. These and other defects in analysis can be brought out in cross-examination of the state's expert witness, and/or the defense can hire its own forensic chemist.
(7) Testing during the absorptive phase: The blood, breath or urine test will be unreliable if done while you are still actively absorbing alcohol (it takes 45 minutes to three hours to complete absorption; this can be delayed if food is present in the stomach). Thus, drinking "one for the road" can cause inaccurate test results.
(8) Retrograde extrapolation: This refers to the requirement that the blood-alcohol concentration be "related back," in time from the test to the driving. Again, a number of complex physiological problems are involved here.
(9) Regulation of blood-alcohol testing: The prosecution must prove that the blood, breath, or urine test complied with state requirements as to calibration, maintenance, and procedural requirements for the administration of the test.
(10) License suspension hearings: A number of issues can be raised in the context of an administrative hearing before the state's department of motor vehicles.
(11) Finally, very unlikely, but it occurs: fraud on the part of a police officer.