Reasonable suspicion is a general criminal law concept that also applies to driving under the influence. It requires that officers have an objectively reasonable basis for suspecting criminal activity before detaining someone. It’s a standard that’s lower than probable cause (discussed below). Before pulling someone over, an officer needs only a reasonable suspicion that the motorist has violated the law. An officer can pull you over, for example, after witnessing you swerve across the road, drift in and out of a lane, or commit some other traffic violation.
Probable cause is another standard that applies to all kinds of criminal cases: It’s the measure by which judges evaluate arrests. There’s probable cause for an arrest if the facts support an objective belief that the suspect has committed a crime. So, after pulling you over, but before arresting you for DUI, a police officer must have probable cause to believe that you were too impaired to drive.
Field Sobriety Tests
Police officers use a set of preliminary tests known as field sobriety tests (FSTs) to determine if a DUI suspect is intoxicated. These physical tests—as distinguished from chemical breath and blood testing—assess the driver’s physical dexterity and ability to follow directions. The most common FSTs are:
- standing on one leg
- walking and turning
- counting backwards
- reciting the alphabet
- placing finger-to-nose, and
- Horizontal Gaze Nystagmus (HGN), a test in which the suspect follows the officer’s moving finger.
If field sobriety tests don’t eliminate the likelihood of intoxication, police officers generally administer chemical testing: either a breath test performed with a device known as a breathalyzer or blood sampling. A third, less favored chemical test involves urine analysis (discussed below). All three tests are administered to determine the suspect’s blood alcohol content (BAC).
BAC refers to the proportion of alcohol found in a driver’s blood. BAC—measured as weight per unit of volume—is reported as a percentage of one percent of the driver’s blood. For example, a BAC of.20%, means that 20/100 (or 1/5) of one percent of the driver’s blood is comprised of alcohol. Typically, the level at which a driver is deemed too intoxicated to drive is.08%.
In all states, it’s illegal to drive with a BAC of .08% or more—called DUI per se—regardless of whether you’re ability to drive safely was actually impaired.
DUI, DWI, and OWI
The law prohibiting drunk driving is known in most states by the acronym DUI (for driving under the influence). But many states, including Missouri, use other acronyms, including:
- DUIL (driving under the influence of liquor)
- DWI (driving while intoxicated)
- OMVI (operating a motor vehicle while intoxicated)
- OWI (operating while intoxicated), and
- OUI (operating under the influence).
Regardless of the acronym, the meaning is generally the same: driving under the influence of alcohol or drugs.
Don’t make the mistake of confusing a DWI with “drunk driving.” If you’re arrested for a DWI, the state prosecutor doesn’t need to prove you were “drunk.” Generally, all the state has to show is that you drank enough booze or took enough drugs so that your ability to control the motor vehicle was impaired.
In fact, the prosecution typically doesn’t even need to show that you were actually impaired—for instance, even if you were driving very safely, you’ve committed a DUI by operating a vehicle with a BAC of, say, .10% (see above).
Every state has implied consent laws that generally require a driver to submit to a chemical test when law enforcement is investigating a potential DUI. Drivers can usually choose between a blood or breath test for BAC (and a blood or urine test if drugs are suspected). Some states still use urine tests in alcohol cases, though these are being phased out due to lack of reliability.
An ignition interlock device (IID) is similar to a breathalyzer (a device used to measure blood alcohol content). An IID is connected to a vehicle dashboard or another location inside the vehicle; it requires that the driver breathe into the device before starting the vehicle. If the ignition interlock device detects BAC that’s above the programmed limit, then the engine of the vehicle won’t start.
“Look Back” or “Washout” Period
The “look back” (or “washout”) period is the length of time—usually five to ten years—that a prior DUI conviction stays on an offender’s record for purposes of future punishment. For example, if a driver receives two DUI convictions within four years, the earlier conviction factors into the punishment for the later offense. The court will view the case before it as a second DUI, and impose the statutorily increased penalties. (Penalties tend to increase with each subsequent conviction within the look back period.)
An SR-22 is a document that verifies that someone has automobile insurance. (The “SR” stands for “safety responsibility.”) An insurance company typically prepares the SR-22 and files it with the department of motor vehicles (DMV). The SR-22 is not an insurance policy; it is evidence that the driver has a policy.