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DWI – Driving While Intoxicated

DWI is the abbreviation for “driving while intoxicated.” It is a legal term for operating a motor vehicle inebriated.

  • The legal blood alcohol content (BAC) limit is .08 in all 50 states,(except Utah (0.05%).
  • It is a function of how much alcohol was consumed over what period of time. There are multiple factors, such as weight, age and gender, which effect it.


This percentage is what determines whether a person was operating a motor vehicle while impaired by alcohol, and if they were capable of operating a vehicle safely, or not.

A person’s BAC is the percentage of alcohol to blood, such as 0.10 percent (i.e., 0.10 grams of alcohol per deciliter of blood).

  • For example, a 160-pound man, 1 hour after consuming two standard drinks on an empty stomach will have a BAC of approximately 0.04 percent. 


The BAC has a measurable effect on a person’s reaction time, mental capabilities and behavior (see chart).

Predictable Effects of alcohol levels on driving

Drivers are not all impaired at the same BAC’s. For example, a driver can divide attention between two visual information sources by 0.02 percent or lower BAC. However, it is not until a BAC of 0.05 percent or more is when impairment occurs consistently in eye movements, glare resistance, visual perception, reaction time, certain types of steering tasks, information processing, and other aspects of motor skills.

Drinking alcohol impairs a wide range of skills necessary for carrying out these tasks. This Alcohol Alert examines alcohol impairment of driving skills and describes factors that increase motor vehicle crash risk.

The Law

If law enforcement suspects someone is driving after drinking, they will  perform breathalyzer or other type of test to see if their BAC is equal to or greater than the legal limit (0.08). If convicted, a “first offense” is considered serious.

  • In many states, drunk driving is treated as a misdemeanor, but repeat offenders might face felony charges.
  • Penalties increase if the BAC is at least 0.15%.

If the police suspect someone may have been drinking while driving, they will test them to see if they are over the legal limit. First, the driver performs specific physical tests such as walking a straight line. Then, a ” breathalyzer gives the officers a rough idea what the driver’s approximate BAC level until doing an actual blood test.

  • second higher level in some states constitutes an “aggravated” category with more severe consequences.

For repeat offenders or those with more severe drinking problems, a therapy that lasts for at least 12 months and includes intensive programs focused on the individual appears to be most effective.

Sentencing Guidelines

Treatment of convicted DWI drivers generally emphasizes drinking behavior modification. The type and duration of treatment depend on the severity of the person’s drinking problem and DWI history. DWI offenders with less severe drinking problems benefit most from educational programs, although no known model effectively reduces recidivism or alcohol-related crashes.

  • These same sets of laws apply to driving under the effects of narcotics, including prescription medication.

Some states now require offenders to use the “ignition interlock” device. They are a “breathalyzer” installed on a motor vehicle’s dashboard. Before the car starts, the driver first must exhale into the device and pass a BAC test.
Legal sanctions, such as driver’s license suspension and court-ordered alcoholism treatment, are designed to deter drinking and driving. Driver’s license suspension and license revocation seem to be the most effective deterrents among the general driving population. However, a meta-analysis of strategies concluded that the most effective means for reducing re-arrest for driving under the influence of alcohol DWI and crashes were a combination of license suspension and interventions such as education, psychotherapy, counseling, and some follow-up.

Standard Drink

For purposes of estimating, it is important to approximate the amount of alcohol in a “standard drink.” Although not exact, a “standard drink” is considered to be the following:

  • 5 ounces of wine
  • 12 ounces of beer
  • 1/12 ounces of hard liquor
Alcohol drink equivalency chart


  • An estimated 32% of fatal car crashes involve an intoxicated driver or pedestrian (NHTSA).
  • Three thousand nine hundred fifty-two fatally injured drivers tested positive for drugs (FARS).
  • Over 1.1 million drivers were guilty of driving under the influence of alcohol or narcotics in 2015 (CDC).
  • Every day nearly 29 people in the U.S. die in alcohol-impaired vehicle crashes( NHTSA).
  • According to NIAAA, drinking and driving claims more than 15,000 lives per year.
  • According to the department of justice, there were 1.1 million DWI arrests in 2015.
  • Alcohol-related crashes cause an estimated $45 billion in damages a year.
  • Drunk driving costs the U.S. $199 billion per year.
  • A drunk driver has driven drunk an average of 80 times before his first arrest.
  • Every 2 minutes, a person is in a drunk driving crash.
  • The rate of drunk driving is highest among 21 to 25-year-olds.
  • In 2015, 29.1 million people admitted the driving under the influence of alcohol.
  • One person is killed every 51 minutes due to drunk driving.