Reasonable suspicion and probable cause may lead to a DUI arrest
We often hear that in order for an officer to stop a motorist on the roadway, he must have a reasonable suspicion of criminal activity. This means that at the time of the stop, the officer believes that the driver was doing something illegal, even if they end up being wrong. With DUI stops, typically the officer will observe the driver behaving recklessly on the road. For example, an officer may pull over someone who is switching lanes frequently, making illegal turns or braking unnecessarily. Even a burned-out brake light, which has nothing to do with drunk driving, can be enough for an officer to stop a driver.
With that reasonable suspicion, the officer is permitted to detain the driver for a brief period of time in order to conduct an initial investigation. If the officer suspects that the driver is under the influence of drugs or alcohol even after the inspection, the officer will typically administer a blood alcohol test to measure the blood alcohol level of the driver. The test most commonly used is a breath test. An officer may also ask the driver to submit to a field sobriety test.
While reasonable suspicion is enough for a brief stop and investigation, in order to make an arrest, there must be probable cause. Probable cause means that the officer has enough evidence to show that the driver has most likely committed a crime. Probable cause is a higher standard than reasonable suspicion. For a DUI arrest, the officer will typically have evidence in the form of test results. In a number of DUI cases, the results of the field sobriety test or BAC test indicate that the driver was drunk at the time of the stop. These results, however, can be inaccurate if the test was not properly calibrated or administered effectively.
Without reasonable suspicion for the initial stop and probable cause for the arrest, a DUI case against a driver could be dropped altogether.