When police stop a motorist to investigate whether he or she is driving drunk, the officer's primary objective is to collect evidence that will validate a DUI arrest. A roadside field sobriety test is one of the main methods that police use to determine whether an arrest is warranted.
Unfortunately, numerous studies have shown that police officers are prone to overestimate significantly how many drivers are actually legally drunk based on what they observe during field sobriety tests such as the one-legged stand or the heel-to-toe straight-line walk and turn.
Scientifically proven to be inaccurate
The truth is these are unnatural physical movements that require a level of coordination and balance that many motorists simply do not have, even when they are perfectly sober. The tests are scientifically proven to have a significant degree of inaccuracy built into them.
In the mid-1970s, the National Highway Traffic Safety Administration (NHTSA) commissioned the Southern California Research Institute (SCRI) to help determine which roadside field sobriety tests were the most reliable. The researchers determined that three of the tests were the most accurate:
- Horizontal Gaze Nystagmus (HGN)
- One-leg stand
The SCRI study determined the HGN test is accurate 77 percent of the time, the walk-and-turn test is accurate 68 percent of the time and the one-leg stand test is accurate 65 percent of the time. The authors determined the high rate of inaccuracy was due in part from police officers ignoring evidence that failure to successfully perform the tests often resulted from factors other than alcohol.
Drunk driving charges can be challenged
Police officers make mistakes when assessing motorists' ability to drive safely and whether their blood alcohol content (BAC) is over the legal limit. It is always smart to work with an experienced DUI defense lawyer if you face drunk driving charges.