When a law enforcement officers witnesses a driver and has reason to suspect that s/he is intoxicated or under the influence of drugs, a DWI investigation commences. Said investigation must adhere to National Highway Traffic Safety Administration (NHTSA) protocols including three specific phases through which all DWI investigations proceed.
Before any investigation can commence, an officer must have reasonable suspicion to stop a suspected drunk driver. Reasonable suspicion is a standard the Supreme Court established in 1968 that is less than the probable cause standard stipulated in the Fourth Amendment of the US Constitution. Whereas probable cause uses a reasonable person standard, reasonable suspicion uses a reasonable police officer standard. This standard permits law enforcement officers—based on their experience and training—to briefly stop and detain a person if the officer has reason to believe the person is engaging in criminal activity.
There are several circumstances which would provide a police officer the reasonable suspicion to come into contact with a suspected drunk driver. The most common reason is the observation of erratic or suspicious driving—such as swerving, driving the wrong way, speeding or driving too slowly, or driving with the lights off, for example. An officer can also stop a vehicle for a lesser traffic offense and then notice signs of intoxication warranting starting an investigation. Other circumstances which may warrant a police officer stopping a motorist include a traffic accident or responding to a report by another person that a motorist is driving erratically.
The NHTSA put forth three specific phases police officers should use when conducting a DWI investigation. Phase 1 is the “vehicle in motion,” Phase 2 involves “personal contact” with the motorist, and Phase 3 is the “pre-arrest screening.”
More specifically, Phase 1 addresses the officer’s observations of the suspect’s driving. Phase 2 begins when the officer actually stops the motorist. If the officer notices any symptoms indicative of the subject being under the influence such as an odor of alcohol, slurred speech, red or bloodshot eyes, droopy eyelids, confusion, poor fine motor skills, for example, s/he likely has reasonable suspicion to make contact with the driver. Finally, Phase 3 occurs when the officer administers standardized field sobriety tests (SFSTs) and questions the subject. Phase 3 also encompasses the administration of any post-arrest chemical tests.
Field sobriety tests
As mentioned, during Phase 3, officers administer SFSTs. The NHTSA has published many training manuals on how to best conduct these tests, their accuracy, and those people for whom certain tests are not recommended. For example, the walk-and-turn test and one-leg stand test are 65-68 percent accurate for most suspected drunk drivers; however, said tests are not validated for those with medical conditions or injuries, who are morbidly obese, or who are 65 years of age or older. Along with the horizontal gaze nystagmus test, these three tests are, largely, validated by the NHTSA.
There are other field sobriety tests officers may use to determine if someone is under the influence. These include the finger-to-nose test, finger count test, counting backward, reciting the alphabet, the Romberg balance test, and administering a preliminary alcohol screening (PAS) test or preliminary breath test (PBT) which involves having the suspect breathe into a small, handheld breathalyzer device.
While you may refuse to participate in SFSTs—except for the preliminary breath test which could result in additional charges for violating the state’s implied consent law—said refusal just increases the officer’s probable cause to arrest you.