All 50 states have established what is known as a blood alcohol concentration (BAC) limit. Most states set that limit at .08%. The law presumes (regards) a person has been driving while impaired (DWI) if their blood alcohol concentration (BAC) equals or exceeds that limit (typically 0.08% or higher).

To put it simply, if an individual who is operating or controlling a motor vehicle takes a BAC test that reveals a BAC of .08% or higher, then the person, by definition, is driving while impaired (sometimes referred to as driving while intoxicated). The offense of driving while impaired or intoxicated is regarded as a “per se” (in and of itself) offense – a number of .08 or higher is by itself enough evidence for a conviction.

The .08 level does not matter whether the person with the level shows physical or mental signs of impairment or if the person operates the vehicle safely. No matter what, .08 = driving while impaired.

When it comes to DWI, there is no “correlation” between BAC and impairment. By definition, a BAC of .08 is considered impaired.

A number of factors also influence the BAC of a person at any given moment. After consuming a given amount of alcohol, a person’s BAC rises according to the following factors.

Among these factors are:

  • Age
  • Gender
  • Weight
  • Body Fat Percentage

What Is Driving Under the Influence (DUI)?

Like DWI, driving “under the influence” (DUI) is a criminal offense. In order to determine whether a person is driving under the influence, their blood alcohol content does not need to be at or above a certain level.

“Driving under the influence” occurs when:

  • There is a reduction in their ability to drive safely; and
  • A person’s diminished abilities are directly related to their state of intoxication.

DUI is a crime that has both a cause and an effect. In order for a crime to be proven, there must be a particular result (diminished driving ability) caused by a particular cause (intoxication). Both cause and effect must be proven.

Higher BAC levels are associated with impaired or diminished driving ability. The higher the BAC, the more drinks one consumes. In general, the higher the blood alcohol content (BAC), the greater the degree of impairment or diminished driving ability.

The National Highway Traffic Safety Administration describes the positive correlation between BAC and impairment in specific detail:

  • When a driver has a BAC of .02, both their visual function and their ability to perform two tasks at once decrease.
  • BAC levels of .08 cause the same effects as .02, as well as short-term memory loss, inability to control driving speed, reduced ability to process information (e.g., signal detection), and impairments in perception.

In addition to causing the same effects as .02 and .08, a BAC of .10 reduces one’s ability to maintain lane position and brake appropriately.

As one’s ability to drive diminishes – as the BAC rises – the more likely it becomes that they have committed the offense of driving under the influence.

How Does the Blood/Breath Alcohol Concentration (BAC) work?

The amount of alcohol in a person’s bloodstream is measured by their blood alcohol concentration. An individual’s breath alcohol concentration is a measurement of how much alcohol they have in their body.

“Blood alcohol content” is also known as “blood alcohol concentration” and “blood alcohol level.”

Breath alcohol content is also known as “breath alcohol concentration” and “breath alcohol level.” These terms are abbreviated as “BAC.”

The amount of alcohol in a person’s bloodstream is measured in milligrams (mg) per 100 milliliters (ml). In most cases, the number is expressed as a percentage (e.g., 0.08, 0.15). An individual with a BAC of .10 percent has one part alcohol per 1,000 parts blood in their blood supply. The level of blood alcohol concentration is determined by testing the blood.

Breath alcohol concentration can also be used to measure impairment. An indirect (approximate) measure of blood alcohol concentration is breath alcohol concentration. In a breath analyzer, commonly referred to as a “breathalyzer,” alcohol concentration is measured.

The user exhales into the breath analyzer during a breathalyzer test.

During a series of chemical reactions, breath ethanol (ethanol is the intoxicating agent found in alcoholic beverages) is converted into an electric current. A breath analyzer device displays a person’s breath alcohol concentration as a percentage based on the amount of current produced.

Zero Tolerance Laws: What Are They?

Zero Tolerance laws ensure that any underage driver found with a Blood Alcohol Concentration (BAC) level over 0.00 will be found guilty of impaired driving and face serious penalties.

What Are the DUI Penalties for Underage Drivers?

Every state imposes stricter penalties on underage drivers who have consumed alcohol, but not all states have adopted Zero Tolerance laws. As in all alcohol-related vehicle stops, a suspected drunk driver will suffer administrative penalties – most commonly a suspended license – separate from any criminal penalties imposed if the driver is convicted of drunk driving (DUI / DWI).

The actual penalties imposed will vary from state to state:

  • California
    • Administrative Penalties
      • Refusing e to take a chemical test after a DUI arrest, or if a minor with a BAC higher than 0.00% will have a license suspended for one year
    • Criminal Penalties
      • A DUI conviction may result in:
        • Jail time
        • Paying a fine
        • Revoked for one year or until 18, whichever is longer
        • A vehicle may be impounded for up to six months, with storage fees owed by the defendant
  • Florida
    • Administrative Penalties
      • If you refuse to take a chemical test, even at the initial stop, your license will be suspended for one year
      • A BAC level of 0.02% or higher will result in a 6-month suspension of your license
      • A BAC of 0.05% or higher will result in the suspension of your license until you complete a substance abuse evaluation and course
    • Criminal Penalties
      • If convicted of DUI, penalties include:
        • Jail time
        • Paying a fine
        • License revoked for a minimum of 6 months
        • Attendance at DUI school and potential treatment
  • Illinois
    • Administrative Penalties
      • If you refuse a chemical test, your license will be revoked for at least six months
      • In the event that a BAC level is higher than 0.00%, a license will be revoked for at least 3 months
    • Criminal Penalties
      • If convicted of DUI:
        • Jail time and paying a fine
        • Revoked for a minimum of 2 years
  • New York
    • Administrative Penalties
      • Refusing to take a chemical test will revoke a license for at least one year
      • If a BAC level is 0.02% or higher, the driver’s license will be suspended for six months, as well as
        • Paying a civil penalty
        • Paying a license re-application fee
    • Criminal Penalties
      • If you are convicted of DWI:
        • Jail time and fines
        • License revoked for a minimum of 1 year
  • Texas
    • Administrative Penalties
      • Refusing to take a chemical test will result in a license suspension for at least 6 months
      • If the BAC level is higher than 0.00%, the driver’s license will be suspended for at least two months
    • Criminal Penalties
      • Under 21:
        • Pay a fine and perform community service
        • Attend alcohol-awareness classes
        • The license will be suspended for 2 months
      • Under 18:
        • Pay a fine and spend 72 hours to 180 days in jail
        • Attend alcohol-awareness classes and perform community service
        • A three-month suspension will be imposed on the license

What Should I Do If I Am Arrested for Drunk Driving?

If you are arrested for DUI or DWI, you should speak to an experienced DUI/DWI lawyer to learn more about your rights, defenses, and what to expect from the legal system.