Drunk driving is the act of operating a motor vehicle under the influence of alcohol and/or drugs to the degree that mental and motor skills are impaired. It is illegal in all jurisdictions within the U.S. The specific criminal offense is usually called driving under the influence [of alcohol and/or other drugs] (DUI), and in some states driving while intoxicated (DWI), operating while impaired (OWI), or operating a vehicle under the influence (OVI). Such laws may also apply to boating or piloting aircraft.

All states in the U.S. designate a "per se" blood or breath alcohol level that is a crime in itself. This means if your blood alcohol exceeds the level identified by law, you will be charged with a crime. A second criminal offense of driving "under the influence" or "while impaired" is also usually charged in most states, with a presumption of guilt where the person's blood alcohol concentration (BAC) is .08% or greater (units of milligrams per deciliter, representing 8 g of alcohol in 100 deciliters of blood). Some states include a lesser charge — often known as driving while impaired — at a BAC of, for example, .05% or above but less than the legal limit for the more serious charge.

Some U.S. states also increase the penalties for drunk driving (even to the point of making it a felony) if certain other aggravating circumstances are present, such as if the drunk driver caused an accident requiring the hospitalization of another person lasting greater than a specified period of time (often 72 hours), in cases where an accident resulted in property damage exceeding a certain amount (often $500), or where the driver has prior (and relatively recent) convictions for drunk driving. In addition, most states observe administrative laws that further penalize people convicted of DUI, typically enforced by the department that issues driver's licenses. Also, in many states, persons under 21 who purchase, or even attempt or conspire to purchase, alcohol can have their driving privileges suspended (if they already are licensed drivers) or delayed (if not) even if they were not caught actually driving while intoxicated.

Sample timeline of a typical DUI arrest

The following is what can happen when a law enforcement officer has a reason to suspect a driver is intoxicated. Some possible reasons are erratic driving, poor coordination, and/or the presence of the smell of alcohol.

"The Stop"

The officer must approach the person suspected of DUI. If the suspect is in a moving vehicle, the officer has to stop the vehicle. Other situations may require other methods of approaching the suspect. The officer must have reasonable suspicion to "stop" the suspect. Otherwise the officer may violate the suspect's 4th Amendment right to be free from unreasonable search and seizure.

Field sobriety test

The officer will administer one or more field sobriety tests (FSTs). The three "Standardized" Field Sobriety Tests (SFSTs) are

the "Walk and Turn",

the "One-Leg Stand", and the

"Horizontal Gaze" (in which a law enforcement officer observes three distinct types of movement of a person's eyes when tracking a stimulus across their field of vision).

The reliability of SFSTs has also been questioned.
A more recent but widely used field sobriety test involves having the suspect breathe into a small, handheld breath testing device. Called variously a PAS ("preliminary alcohol screening") or PBT ("preliminary breath test"), the units are small, inexpensive versions of their larger, more sophisticated instruments at the police stations, the EBTs ("evidentiary breath test"). These units help the police officer determine if there is probably cause for an arrest.

Chemical test

If arrested, the driver is brought to the police station, and given one or more chemical tests: breath, blood or, much less frequently, urine. Breath test results are usually available immediately and are sometimes given before the actual arrest takes place; urine and blood samples are sent to a lab to determine the BAC. In some jurisdictions, refusing to take a breathalyzer test is an offense in itself, and may carry a presumption of guilt under the law.
If a person is involved in a motor vehicle accident involving a fatality or serious physical injury, and is suspected to be intoxicated, some jurisdictions permit the police to forcibly take a sample of the driver's blood without their consent. This is often done after a warrant is obtained from a judge, although it is increasingly common to force a "draw" without a warrant under the "exigent circumstances" doctrine. While chemical tests are used to determine the driver's BAC, they are unable to determine the driver's level of impairment. State laws usually provide for a rebuttable legal presumption of intoxication at blood alcohol levels of .08% or higher. However, their accuracy is a subject of some dispute. In any case, tests can only determine the BAC at the time the test is taken, which can be higher or lower than when the vehicle was actually operated. Evidence of the BAC at time of driving is often presented in the form of "retrograde extrapolation", a process whereby an expert witness estimates earlier levels based upon average rates of alcohol absorption and elimination.

Next step

If it is determined after arrest that the person's blood alcohol concentration is not above the legal limit of .08%, he will probably be released without any charges. He may, however, still be charged with driving under the influence of alcohol on the basis of driving symptoms, observed impairment, admissions and/or performance on the field sobriety tests. And assuming some evidence of drug usage, he may face charges of driving under the influence of drugs or the combined influence of alcohol and drugs -- in which event, a blood or urine test is likely, or at least the testimony of a specially-trained officer called a Drug Recognition Expert (DRE).
Most of the time, the driver will either be kept in a holding cell (sometimes referred to as the "drunk tank") until they are deemed sober enough to be released on bail or on their "own recognizance", or kept in jail to wait for their first court hearing, called an arraignment.


For more information, go to http://en.wikipedia.org/wiki/Driving_while_impaired