After stopping a driver for a suspected DWI, one of the main ways that officers determine whether or not they need to make an arrest is by having the person go through field sobriety tests. These are mental and physical tests that can be performed on the side of the road, and failure may show the officer that the driver is so impaired that they should not have been driving.
That said, these are not necessarily scientific tests. The officer just makes a judgment call based on what they see. Are the tests really reliable?
Studies have found that, in at least 10% of cases, the field sobriety tests get it wrong. It is also noted that officers must be properly trained to carry out the tests for them to work, as a mistake by the officer could lead to a false arrest. The three main tests considered are the one-leg stand, the walk-and-turn and the horizontal gaze nystagmus (HGN).
One potential issue to consider is how a person would do on the tests if they were sober. For instance, the tests use the one-leg stand to gauge balance. What if the person is naturally uncoordinated and struggles with balance issues? What if they have a medical condition like vertigo? What if they are simply tired after a long day of physical labor, so the tests are more difficult than they would be otherwise? What if it’s dark or rainy, making it harder to do the tests on the side of a random road?
There are just too many factors to consider for these tests to work 100% of the time, and those who get arrested must know what options they have.