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DUI and DWI

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Key facts: Driving under the influence is illegal in every state, most commonly enforced through a per se BAC limit of 0.08%, though Utah sets its limit at 0.05% and all states bar any detectable alcohol for drivers under 21.[1][2]

Driving under the influence (DUI) and driving while intoxicated (DWI) are criminal driving offenses in all states, covering dangerous driving impairment caused by alcohol, drugs, or other controlled substances.[1]Most charges follow a breath or blood test showing a blood-alcohol content (BAC) at or above the federal threshold of 0.08%, though state law can set a different legal limit.[1]

Overview

DUI and DWI laws criminalize operating a vehicle while impaired by alcohol, drugs, or other controlled substances, and every state has some version of these offenses.[1]The terms DUI and DWI may be used interchangeably or may carry separate legal meanings depending on the state.[1]Suspicion of impairment is usually triggered when an officer witnesses dangerous or erratic driving, and testing or arrests can also occur at sobriety checkpoints set up by police.[1]The Supreme Court upheld sobriety checkpoint programs as constitutional, finding that Fourth Amendment concerns over seizure were outweighed by the public interest in road safety.[1]A driving stop or checkpoint encounter is often the first step in the broader arrest process that follows a DUI charge.[1]

Per se blood alcohol limits

Most impaired-driving charges are based on a per se law, meaning that a BAC at or above a set threshold is itself illegal, regardless of whether the driver appears impaired.[1]The federal BAC limit referenced in most state per se laws is 0.08%, though state law may set a lower limit.[1]Forty-nine states and the District of Columbia use the 0.08% threshold, while Utah makes it a crime to drive with a BAC of 0.05% or above.[2]In all 50 states, drivers younger than 21 are prohibited from operating a vehicle with any detectable blood alcohol, with most states setting that threshold at 0.02% or lower.[2]The national per se threshold used to be higher than 0.08%, and a review of research on lowering it from 0.10% to 0.08% found a median decrease in alcohol-related motor fatalities.[2]A driver with a BAC under the legal limit can still face impaired-driving charges if an officer observes driving that suggests impairment and the driver shows signs of impairment after being stopped, including a failed field sobriety test.[1][2]

Impairment by drugs

DUI and DWI laws are not limited to alcohol; they also cover dangerous driving impairment caused by drugs or other controlled substances.[1]Marijuana-impaired driving has become a growing concern as more states legalize recreational use, and experimental studies have found that recent marijuana use can worsen driving performance.[2]Crash rates have risen in states that have legalized retail sales for recreational marijuana use.[2]Charges related to drug impairment can overlap with separate drug crimes depending on the circumstances of a stop.

Officers can ask drivers to submit to chemical testing of breath, blood, or urine whenever they suspect impairment, and this suspicion is usually triggered by observed dangerous or erratic driving.[1]States typically require that obtaining a driver's license carries an implicit agreement to this testing, a concept known as implied consent.[1]Drivers can refuse chemical testing, but in most jurisdictions refusal results in automatic forfeiture of driving licensure.[1]Administrative license suspension for drivers who fail an alcohol test or refuse testing is considered an effective measure against impaired driving, along with alcohol interlocks for people convicted of impaired driving and sobriety checkpoints.[2]These enforcement tools intersect with constitutional protections discussed in the broader area of constitutional rights of the accused, including search and seizure limits under the Fourth Amendment.[1]

Penalties

The sources summarized here do not detail specific DUI penalty schedules, and the consequences of a conviction vary significantly by state. General information about how courts approach punishment, and how prior convictions or injury can affect outcomes, is addressed in material on criminal sentencing. People facing a DUI charge may also want to review information on the criminal process generally, since the steps following arrest, such as bail and pretrial release and arraignment, apply to DUI cases as they do to other criminal charges.

Terminology across states

Driving while under the influence (DUI) and driving while intoxicated or impaired (DWI) are both used across the country, and the terms may be used interchangeably or have separate meanings depending on the state.[1]Because definitions differ, the exact label used in a given case does not necessarily indicate whether the charge is a misdemeanor or felony; that classification depends on state law and the facts of the case. Readers trying to understand how a specific charge is defined in their state may want to start with general background on what criminal law is and the elements of a crime before looking at state-specific statutes.

Entries in this section

Further entries planned for this section (not yet published):

Common questions

What is a DUI?

DUI stands for driving under the influence, a criminal driving offense that exists in every state and covers dangerous driving impairment caused by alcohol, drugs, or other controlled substances.[1]Depending on the state, DUI may be used interchangeably with DWI (driving while intoxicated or impaired), or the two terms may have separate legal meanings.[1]

What blood alcohol level is illegal?

Under the federal per se limit used by most states, a BAC at or above 0.08% is illegal, though state law can set a lower limit.[1]Forty-nine states and the District of Columbia use the 0.08% threshold, Utah's limit is 0.05%, and every state bars drivers under 21 from having any detectable alcohol, generally at 0.02% or lower.[2]A driver can still be charged with impaired driving even with a BAC under the legal limit if an officer observes signs of impairment.[1]

What happens if you refuse a breath test?

Drivers can refuse chemical testing of their breath, blood, or urine, but in most jurisdictions that refusal results in automatic forfeiture of driving licensure, because obtaining a license implies consent to such testing.[1]Administrative license suspension for drivers who refuse testing is considered one of the effective enforcement measures against impaired driving.[2]

Can police set up checkpoints to test drivers for DUI?

Yes; testing and arrests for DUI and DWI can occur at sobriety checkpoints set up by police, and the Supreme Court upheld such checkpoint programs as constitutional, finding that Fourth Amendment seizure concerns were outweighed by the public interest in road safety.[1]Sobriety checkpoints can act as a deterrent to impaired driving even when they do not result in many arrests.[2]

Does a DUI charge always require a breath or blood test result?

No; some states allow charges to be brought without chemical testing results if there is suspicion of impairment based on erratic or dangerous driving combined with a failed field sobriety test.[1]In all states, a driver with a BAC under the legal limit can still be charged if an officer observes driving suggesting impairment and the driver shows signs of impairment after being stopped.[2]

References

All sources retrieved November 2026.

  1. ^ a b c d e f g h i j k l m n o p q r s t u v w x y z 26 27 "Driving under the influence (DUI) (Wex)". Legal Information Institute, Cornell Law School. Retrieved November 2026.
  2. ^ a b c d e f g h i j k l m n "Alcohol and drugs". Insurance Institute for Highway Safety. Retrieved November 2026.