DUI stands for Driving Under the Influence, while DWI stands for Driving While Intoxicated or Driving While Impaired. "OWI," or Operating While Impaired, is also used in some cases, as is "DUID," or Driving Under the Influence of Drugs. These terms refer to driving while under the effects of alcohol or drugs that impair judgment—a serious crime. DUI and DWI may sometimes be used interchangeably or, in some states, be recognized as different crimes.
The drugs in use do not have to be illegal for a DUI or DWI to be issued; they can be narcotics, over-the-counter medications, or prescription drugs. The focus, instead, is on impaired driving, which is dangerous to both the driver and others on the road.
Differences Between DUI and DWI
Depending on the state, the definitions and repercussions of a DUI and/or DWI charge vary. Many states use the terms interchangeably, as they are legally treated as the same crime. Some states differentiate between DUI and DWI offenses, however, with a DUI usually being the lesser charge. In these cases, DUIs usually signify less intoxication, as determined by a person's blood alcohol content (BAC) at the time of arrest.
Legal Limits for Blood Alcohol Level
In the U.S., all states classify driving with a BAC 0.08% or higher as impaired driving. Some states, such as Colorado, impose other criminal penalties for a BAC above 0.05% and similar, stricter penalties for previous offenders. Drivers under 21 typically cannot have a BAC above 0.02%, or are subject to zero tolerance laws, because young adults under 21 are not legally allowed to drink in the U.S.
Other authoritative bodies may also set special BAC limits in an effort to further discourage drunk or drugged driving and more severely penalize offenders. For instance, the Federal Motor Carrier Safety Administration mandates a 0.04% BAC limit for drivers of commercial vehicles that require a commercial driver's license.
When drivers are suspected of impairment, officers may pull them over and require them to perform a series of physical tests (e.g., walking in a straight line, standing on one leg) and undergo a breathalyzer test, which roughly detects BAC levels. Many states issue automatic penalties for refusing a breathalyzer test. There are other automatic penalties for those who have a BAC level above 0.08%, and even below that level, drivers can have civil liability or other criminal guilt, especially if impairment is obvious. For example, in the state of Arizona, any driving impairment that might be caused or related to alcohol consumption can be a civil or criminal offense.
To learn about BAC limits around the world, see Wikipedia's entry on drunk driving laws by country.
Individual states have the power to regulate DUI and DWI penalties, and so laws and subsequent penalties vary considerably from state to state. Among those states that differentiate between DWI and DUI, some will occasionally reduce a DWI charge to a DUI in the case of first time offenses, defendant remorse, and a blood alcohol level that was not significantly over the legal limit. Below are the different DUI and DWI penalties from some of the most populated states.
DUI Penalties in California
DUIs and DWIs are the same in California; the terms are used interchangeably, but "DUI" is more common. First time DUI/DWI offenders may be jailed for 4 days or up to 6 months, pay fines between $1400 and $2600, and have their driver's license suspended for 30 days or up to 10 months; some counties may require the installation of an ignition interlock device. Second and third offenses carry heavier penalties and may result in up to a year-long jail sentence. Repeat offenders and drivers under 21 may not drive with a BAC level above 0.01%. More info.
DUI/DWI in Texas
The state of Texas charges those under 21 who are driving impaired with a DUI, in accordance with the state's zero tolerance policy for under 21 driving. Impaired drivers over 21 are charged with a DWI. As such, "DWI" is the more common term in Texas, and it also carries harsher penalties. First time DWI offenders spend a minimum of 3 days or up to 180 days in jail, pay up to $2,000 in fines (more in the case of child endangerment), and have their license suspended for 90 days or up to a year. Second and third time offenses carry heavier penalties, such as a required ignition interlock device for future driving. A third time offense results in a minimum of 2 years in jail. More info.
DWI Laws in New York
"DUI" is not used in New York, but DWI and DWAI (Driving While Ability Impaired) are. DWAI refers to driving that is below the 0.08% BAC limit but is still clearly impaired, while DWI is the more common term and refers to driving at or above the 0.08% limit. First time DWI offenders in New York may spend up to a year in jail, pay between $500 and $1000 in fines, and have their license suspended for a minimum of six months. The penalties for second and third time offenders are much more drastic, with potential jail time up to 4 and 7 years, fines between $1,000 and $10,000, and a minimum one-year license suspension; offenders are also required to have an ignition interlock device installed. More info.
DUI/DWI in Florida
DUIs and DWIs are the same in Florida and may be used interchangeably. First time DUI/DWI offenders may spend between 6 and 9 months in jail, are fined between $500 and $2,000, have their license suspended for 180 days or up to a year, and must have an ignition interlock device installed for future driving. Compared to other states, Florida tends to emphasize license suspension over jail time for second and third time offenders. More info.
DUI Laws in Illinois
Though DWI and OWI may sometimes be used in common discussion or news reporting, only DUI is recognized in Illinois state law. First time DUI offenders can spend up to a year in jail, be fined up to $2,500, have their license suspended for a minimum of one year, and are required to install an ignition interlock device. Both jail time and license suspension are emphasized for second and third time offenders. There are zero tolerance laws for people under 21. More info.
In all states, community service and drug/alcohol education or rehabilitation programs are also common repercussions for driving while impaired.