Expert Witnesses in DUI / DWI Cases

The use of experts is extremely important in DUI / DWI, drunk driving, or driving under the influence of alcohol or drugs (DUID) cases. Because the prosecution will be putting the arresting officer and the criminalist before the judge during his or her case to testify as to why the defendant is guilty, it is vital that the defense is able to put forward its own witnesses to counter that. Experts can be called to discuss a variety of topics, but their primary purpose is to support the idea that there are other possible explanations for the prosecution’s evidence that the defendant was drunk driving. Experts can talk about chemical tests, field sobriety tests, accident reconstruction, scientific aspects of being under the influence, and so on.

Chemical Tests: Experts will discuss possible flaws with both breath and blood tests, such as that the breath machine is not properly calibrated or fermentation occurred with the blood and a higher alcohol reading was the result. There are a variety of ways an expert can attack the chemical tests.

Field Sobriety Tests: Experts can use a person’s performance on field sobriety tests (FSTs) to support their opinion that the motorist accused of DUI was not under the influence at the time of driving. If the FST’s are performed well, they will use this to show that there was no physical impairment (if there is good balance, no swaying, etc.) and no mental impairment (if the person followed instructions, counted in correct order, etc). Mental and physical impairment are very important because any good expert will testify that mental impairment always precedes physical impairment when a person is intoxicated. This means that if there was no evidence of mental impairment, but was some physical impairment, the physical impairment was probably due to something other than intoxication (such as an injury or poor testing conditions).

Alcohol Level at Time of Driving vs. Alcohol Level at Time of Testing: Experts are often called to testify in order to rebut the presumption that if a person was drunk at time of the chemical test that they must have been drunk at the time of driving. Since the chemical tests are always given at least many minutes, sometimes even an hour or two after driving, the blood alcohol content (BAC) very often is not the same at both times. Sometimes this can be good for the defense’s case because under certain circumstances the defendant’s BAC could be rising, which means it is higher at the time of the test than when driving. This is a very technical area, and an expert is essential to explain it to a jury and to raise reasonable doubt as to whether the defendant was over the legal limit at the time of driving.

Accident Reconstruction: It is often helpful (especially in a felony DUI / DWI arrest) to have an expert in the field of accident reconstruction. Whenever there is a DUI / DWI, DUID (driving under the influence of drugs), drunk driving, or any type of drinking and driving arrest along with an accident, the passions of the jury will likely be inflamed. As such, it is essential that an accident reconstruction expert be available to testify regarding the mechanics of the accident, and to offer opinions regarding whether or not the accident was the fault of the impaired driver, the other party, or would have been unavoidable regardless of the impairment or non-impairment of the accused DUI / DWI motorist.