State prosecutors building driving while intoxicated (DWI) cases usually have several types of evidence. They may have crash reports or video footage from a police cruiser’s dashcam showing questionable driving practices. They may have chemical test results that show that a driver was clearly over the legal limit for their blood alcohol concentration (BAC) given their age and type of license.
Frequently, there is also video footage and officer testimony related to the driver’s performance on field sobriety tests. Field sobriety testing is a standard component of most DWI traffic stops. What role do they play in DWI cases?
Providing probable cause
Police officers do not automatically have the authority to demand chemical testing or arrest someone during a traffic stop. Implied consent rules only apply in scenarios where an officer can show that they already had the probable cause necessary to initiate an arrest.
Usually, field sobriety tests play an important role in establishing that probable cause. If a driver cannot walk in a straight line or stand on one leg, that can be an indicator of chemical impairment. Even in cases where they don’t display obvious impairment by stumbling, the horizontal gaze nystagmus test can serve as evidence of chemical intoxication.
Officers look at involuntary spasms in the eye muscles that become more pronounced when people are under the influence. Failing any of those tests can give an officer the grounds they need to arrest an individual.
Bolstering a case in court
As previously mentioned, prosecutors may play footage of poor performance on field sobriety tests during court proceedings. Officers may also testify about how a driver performed. Such information can help a prosecutor meet the burden of proof necessary to obtain a DWI conviction.
However, as with chemical breath testing, there are opportunities for false positives during field sobriety testing. There could be other explanations for poor test performance beyond intoxication. Sometimes, drivers can work with lawyers to present medical evidence that raises questions about the usefulness of field sobriety test results.
Challenging field sobriety tests can be an important element of a DWI defense strategy. Drivers who can raise questions about why they performed poorly or the legality of a traffic stop may be able to avoid a conviction that could lead to incarceration and other penalties.