How Blood Alcohol Content (BAC) Levels Impact a Person’s Ability to Drive
In Arizona and every other state in America, if you drive with a blood alcohol level of 0.08 percent or higher you can be arrested for Driving Under the Influence (DUI) or a similar offense. While some states have a lower limit, no states allow people to drive with a blood alcohol content (BAC) that is 0.08 percent or greater. Many people think that means it's safe and legal to drive with a blood alcohol concentration (BAC) of less than 0.08 percent. However, that is not always the case. Arizona law allows impaired drivers who are below the legal limit to be charged with DUI. It can also be dangerous to get behind the wheel after consuming any amount of alcohol, as BAC levels impact a person's ability to drive well before hitting 0.08 percent.
What is Blood Alcohol Content?
Blood alcohol concentration (BAC) is defined as the weight of alcohol a person has in a certain volume of their blood. When a person drinks alcoholic beverages, the alcohol is absorbed directly through the walls of their stomach and small intestine. It then enters their bloodstream, where it accumulates until their liver is able to metabolize the alcohol.
A person's BAC increases based on a variety of factors including:
- The number of drinks they consume
- The size of the drinks
- How fast they drink
- Any medical conditions
- Any medications in their system
- Their biological sex
- Their weight
- The amount of food in their stomach
Why BAC Levels Impact a Person's Ability to Drive
Alcohol reduces the brain's ability to function by impairing thinking, reasoning, muscle coordination, and small muscle control. These mental functions are all crucial when operating a motor vehicle, and the deterioration of these functions makes it difficult for an impaired person to drive safely.
As a person's BAC level increases, the negative impact on their brain and central nervous system also rises. When the alcohol level in a person's system reaches 0.08 grams of alcohol per deciliter of blood (0.08 percent BAC), the risk of a drunk driving accident greatly increases. However, the effects of alcohol on a person's mental state can impact their ability to drive well before their BAC reaches 0.08 percent. According to the National Highway Traffic Safety Association (NHTSA), 1,878 people died in 2018 from alcohol-related accidents caused by drivers with BACs below 0.08%.
How BAC Levels Impact a Person's Ability to Drive
The following information was provided by the U S Centers for Disease Control and Prevention (CDC) regarding the typical effects of alcohol at various BAC levels, and how those effects impact a person's ability to drive. The associated number of drinks for each BAC level shows the approximate amount of alcohol that a 160-pound man would have to consume in a one hour period to reach the listed BAC level. However, because of the many various factors that can impact a person's BAC level, the number of drinks is just an estimate and should not be used as a guide for determining a specific person's BAC on any specific occasion.
BAC of 0.02 Percent
At a BAC of 0.02 percent, which is associated with about 2 alcoholic beverages in an hour, a person experiences the following effects:
- Some loss of judgment
- Feeling relaxed
- Increased body warmth
- Altered mood
These effects can have the following impact on a person's ability to drive:
- A decline in their visual functions such as the rapid tracking of a moving target
- A decline in their ability to multitask by performing two tasks at the same time
BAC of 0.05 Percent
When a person reaches a BAC of 0.05 percent, which is associated with the consumption of approximately 3 drinks, the following effects are typical:
- Exaggerated behavior
- Possible loss of small muscle control, such as the ability to focus their eyes
- Impaired judgment
- Feeling good and happy
- Lowered alertness
- Loss of inhibition
The effects of a 0.05 percent BAC can impact a person's ability to drive in the following ways:
- A decrease in physical coordination
- Reduced ability to track moving objects
- Increased difficulty in steering the vehicle
- Reduced response to emergency driving situations
BAC of 0.08 Percent
After reaching a BAC of 0.08 percent, which is associated with drinking about 4 alcoholic beverages, a person will likely experience the following:
- Poor muscle coordination inhibiting balance, speech, vision, reaction time, and hearing
- Increased difficulty in detecting danger
- Impaired judgment, self-control, reasoning, and memory
The impact of these effects on a person's ability to drive may include:
- Inability to concentration
- Short-term memory loss
- Inhibited speed control
- Reduced information processing capability, which impairs signal detection and visual search
- Impaired perception
Due to the increased impact on a person’s ability to function and drive a vehicle at 0.08 percent BAC, the risk of drunk driving accidents greatly increase at this level of impairment.
BAC of 0.10 Percent
Common effects of a 0.10 percent BAC, which is associated with the consumption of 5 alcoholic beverages, include:
- Clear deterioration of reaction time and physical control
- Slurred speech, poor coordination, and delayed thought processes
These effects create a reduced ability to brake when needed and maintain the vehicle's lane position in impaired drivers.
BAC of 0.15 Percent
Once a person reaches a BAC of 0.15 percent, which is associated with having 7 drinks in an hour, they will experience the following effects:
- Considerably less muscle control
- Possible vomiting, especially if the person drank very quickly or has a low tolerance for alcohol
- Extreme balance loss
At this level of BAC, drunk drivers will face substantial impairment in vehicle control, their ability to pay attention to driving, and the visual and auditory information processing systems that are necessary to safely drive a vehicle. In Arizona, people who are arrested while driving with a BAC of 0.15 percent or higher can be charged with Extreme DUI.
What Constitutes a "Drink"
To understand the above drink estimates, it's important to know what is considered to be a standard drink. It's probably less than you think, especially for liquor and wine. It's not uncommon for people to consume multiple standard "drinks" in a standard drink single alcoholic beverage.
A standard drink is determined by however much of the alcoholic beverage is required to contain 14.0 grams (0.6 ounces) of pure alcohol. In general, this amount of pure alcohol is found in the following:
- 12-ounces of beer, which typically has about 5% alcohol content
- 8-ounces of malt liquor, which typically has about 7% alcohol content
- 5-ounces of wine, which typically has about 12% alcohol content
- 1.5-ounces or a “shot” of 80-proof distilled spirits or liquor, which typically has about 40% alcohol content
Common examples of liquors include gin, rum, vodka, and whiskey. These standard drink amounts are just estimates and alcoholic beverages that have a higher alcohol content than is typical will result in higher levels of impairment in the drinker.
