Correlation between Blood Alcohol Level and Impairment

Where You Need a Lawyer:

(This may not be the same place you live)

At No Cost! 

 The Relationship Between Blood Alcohol Level and Impairment

Drinking alcohol and driving a car do not mix. Alcohol use slows reaction time and impairs judgment and coordination; the latter two skills are needed to operate an automobile safely. The more alcohol one consumes, the more those skills become impaired.

What is Blood/Breath Alcohol Concentration?

Blood alcohol concentration is a measurement of the amount of alcohol that is in a person’s bloodstream. Breath alcohol concentration measures the amount of alcohol in one’s breath. The term “blood alcohol content” is also referred to as “blood alcohol concentration” and “blood alcohol level.” Likewise, the term “breath alcohol content” is also referred to as “breath alcohol concentration” and “breath alcohol level.” All of these terms are referred to in abbreviated form as “BAC.”

Blood alcohol concentration levels are determined most precisely through blood testing. The amount of alcohol in a person’s bloodstream is measured in milligrams of alcohol per 100 milliliters of blood. The number is typically expressed as a percentage (e.g., 0.08, 0.15). If an individual has a BAC of .10 percent, that person’s blood supply contains one part alcohol for every 1,000 parts of blood.

Impairment can also be measured through breath alcohol concentration. While a blood test gives an exact, scientifically measured percentage of alcohol in the bloodstream, breath alcohol concentration is an indirect (approximate) BAC. Breath alcohol concentration is measured through a breath analyzer, colloquially called a “breathalyzer.” In a breathalyzer test, the user exhales into the breath analyzer.

A series of chemical reactions result in the breath of ethanol (the intoxicating agent found in alcoholic beverages) being converted to an electric current. The amount of current produced is then displayed on the breath analyzer device as the person’s breath alcohol concentration, also expressed as a percentage.

What is Driving While Impaired (DWI)?

All 50 states have established what is known as a blood alcohol concentration (BAC) limit. In most states, that limit is set at .08%. If an individual’s blood alcohol equals or exceeds that limit, the law presumes the person is driving while impaired (DWI).

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 legal definition, is driving while impaired (“DWI”) (sometimes referred to as driving while intoxicated). It does not matter whether the person with a high BAC level shows physical or mental signs of impairment or if the person is operating the vehicle perfectly safely.

The act of driving while impaired or intoxicated is regarded as a “per se” (in and of itself) offense. A value of .08 or higher is by itself enough evidence for a conviction.

What is Driving Under the Influence (DUI)?

Like DWI, driving “under the influence” (DUI) is a separate criminal offense. Whether a person is driving under the influence is not measured by BACi. Rather, a person is “driving under the influence” if:

  • Their ability to drive safely is diminished
  • The diminishment is the direct result of the person’s being in a state of intoxication

DUI is a “cause and effect” crime. For the crime to be proven, a particular result (diminished driving ability) must be brought about by a particular cause (intoxication). The cause and effect must both be proven.

While BAC does not define “driving under the influence,” BAC does matter. That is because; higher BAC levels are associated with higher levels of diminished or impaired driving ability. The more drinks one consumes, the higher the BAC becomes. The higher the BAC, the greater the degree of diminished driving ability or impairment.

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

  • A BAC of .02 has the following effects on driving: visual function declines, and the person loses the ability to perform two tasks at the same time
  • A BAC of .08 has the effects associated with .02 and is also associated with inability to control driving speed; impaired visual perception; short-term memory loss; reduced information processing capability (e.g., signal detection); and impaired perception.
  • A BAC of .10 has the effects associated with .02 and .08, as well as the effect of reducing one’s ability to brake appropriately and maintain lane position

The more one’s ability to drive diminishes, the more likely it becomes that an individual has committed the offense of driving while under the influence.

What Are the Consequences for Conviction of a Drunk Driving Crime?

One of the most serious potential DUI consequences is jail time. How much jail time can depend on whether the DUI was a first offense, the blood alcohol content (BAC) of the driver and how much it was over the legal limit, and whether anyone was killed or injured because of the driver’s impairment.

Punishments for a DUI offense include:

  • Incarceration: In all states, a DUI first offense is handled as a misdemeanor and punishable by up to six months in jail. For felony DUI convictions, which can occur where there is serious injury, death, or an especially high BAC, a year or more imprisonment is a possibility. Repeat DUIs can result in sentences of three years or more.
  • Fines: A conviction for a DUI can result in fines ranging anywhere from $500 to $2000.
  • Loss of driving privileges: The offender’s driver’s license may be suspended or revoked
  • Vehicle-related penalties: A DUI offender’s car may be confiscated in some states. In addition, a court may mandate the installation of an ignition interlock device on the offender’s car. Such a device requires the driver to blow into a breathalyzer before the car starts. It is designed to prevent an intoxicated driver from operating the vehicle. There are fees to install the device, monthly fees to use it, and fees to have it recalibrated every few months
  • Drug/alcohol treatment programs: A judge can order an offender to go to a treatment program to get their analysis of what kind of program is needed: outpatient or inpatient. The offender will be required to complete whatever the facility recommended.

Note that individuals under 21 may face additional DUI penalties, including, often, driver’s license suspension of a year. Many states have a separate crime for underage drunk driving, and some states set lower acceptable BACs for those under 21 than for those of legal drinking age.

Besides the penalties imposed by the legal system, a DUI conviction may result in the following:

  • Civil lawsuits for bodily injury or property damage that were incurred as the result of an accident
  • Significant increase in auto insurance rates, or cancellation of the policy
  • Loss of opportunity to obtain certain employment, especially jobs involving driving

Do I Need a DUI/DWI Lawyer?

If you are facing charges for a drunk driving violation, it is strongly recommended that you consult with a local DUI/DWI lawyer as soon as possible. A lawyer with experience handling cases involving DUI or DWI charges can assist you in defending your interests and presenting your case before a judge.

Your lawyer can inform you of your legal rights and any potential legal defenses you may be able to raise against the charges. Your lawyer can also advise you whether you should take a case to trial or settle for a more favorable plea deal (if possible). Attorneys are also highly accomplished at negotiating a plea deal, often a reduction from felony to misdemeanor, a shorter period of incarceration, a lower fine, or all three.

If you go to trial, your lawyer can represent you from start to finish. If you need assistance with getting back a license that was temporarily suspended or revoked, your lawyer can also help guide you through this process.

Law Library Disclaimer


16 people have successfully posted their cases

Find a Lawyer