What Are the Effects of Alcohol on Driving?

In Texas, if you drive with a blood alcohol level of 0.08 percent or above, you can be arrested for Driving While Intoxicated (DWI) or a similar crime. While some states have a lower limit, there is no state in America that permits people to drive with a blood alcohol concentration (BAC) of 0.08 percent or higher.

While many people think that means it’s safe and legal to drive with a BAC of less than 0.08 percent, that is not always true. In Texas, intoxicated drivers who lose the normal use of mental or physical faculties with BACs below the legal limit can technically be charged with DWI. As you will see in the rest of this blog, your driving ability can be impaired well before your BAC level reaches 0.08 percent. This means the safest thing (both physically and legally) is to only drive when you have a 0 BAC.

What is Blood Alcohol Concentration?

Blood alcohol concentration, commonly called BAC, is the weight of alcohol that you have in a certain volume of their blood. Alcohol consumption causes alcohol to accumulate in your bloodstream until your liver can metabolize it. This makes the concentration of alcohol in your blood increase.

How BAC Levels Cause Impaired Driving

Alcohol reduces your brain’s functioning by inhibiting your ability to think and reason, and by decreasing muscle coordination and small muscle control. These mental functions are all essential for safe driving when operating a motor vehicle.

As your level of intoxication rises, the effects of alcohol on your brain and nervous system also increase. When your BAC reaches 0.08%, the dangers of alcohol impaired driving rise considerably. 

However, alcohol’s impact on your brain’s functioning can impair your driving skills even before your blood alcohol level reaches 0.08%. In fact, 1,878 people died in 2018 in alcohol-related accidents caused by drivers with BACs below 0.08%, according to statistics published by the National Highway Traffic Safety Administration.

As part of its quest to reduce drunk driving, the U.S. Centers for Disease Control and Prevention (CDC) has provided public information regarding the usual effects of alcoholic beverages at various levels of intoxication. Additionally, the CDC guidance shows how the driving of people with different BAC levels is affected. For your benefit, I’ve summarized this information below.

Driving Impairments at a 0.02% BAC

With a 0.02% BAC (two drinks in one hour), you will generally feel:

  • A minimal amount of judgment loss
  • A sense of warmth and relaxation
  • An altered mood

Experiencing these effects of alcohol can impact your ability to drive in the following ways:

  • Decreasing your visual capabilities and eye movement, limiting your ability to track a moving object.
  • Decreasing your capacity for multitasking, making it difficult to perform two tasks at the same time.

Driving Impairments at a 0.05% BAC

A blood alcohol level of 0.05% (three drinks in one hour) typically manifests in:

  • Exaggerated behavior
  • Impaired judgment
  • Lack of inhibitions
  • Decreased alertness
  • A happy feeling
  • The potential loss of small muscle control

The effects of a 0.05% BAC can impair your driving by causing:

  • Reduced physical coordination
  • Reduced emergency response time
  • Decreased ability to track moving targets
  • Increased difficulty in steering the vehicle

Driving Impairments at a 0.08% BAC

The legal limit of 0.08% BAC (four alcoholic beverages in one hour) will likely cause you to experience the following effects:

  • Severely impaired judgment, self-control, reasoning, and memory
  • Poor muscle coordination that limits balance, communication skills, peripheral vision, reaction time, and the ability to hear
  • Increased difficulty in detecting danger

At this level of intoxication, your BAC may cause the following dangerous effects to your ability to drive:

  • Reduced perception abilities compared to a sober driver
  • Being unable to concentrate on driving
  • Short-term memory loss
  • Limited speed control
  • Diminished information processing capabilities, resulting in impaired signal detection and visual search

Because the progression of your impairment at 0.08% BAC severely impacts your ability to drive a motor vehicle, the chances of being involved in a drunk driving accident increase considerably at this BAC.

Driving Impairments at a 0.10% BAC

Once your BAC reaches 0.10% (five alcoholic beverages in one hour), you typically will suffer from:

  • Noticeable decline in reaction time and physical control
  • Slurred speech, delayed thinking, and poor coordination

This level of intoxication greatly inhibits your ability to brake as needed and to maintain your vehicle’s lane position while driving.

Driving Impairments at a 0.15% BAC

After you arrive at a 0.15% BAC (seven drinks in one hour), your body experiences the following effects:

  • Poor levels of muscle control
  • Potential vomiting, particularly if you drank very quickly or have a lower tolerance for alcohol
  • Extreme loss of balance

At this blood alcohol level, drivers will encounter substantial impairments such as:

  • Loss of ability to control the vehicle
  • Inability to pay attention to driving
  • Diminished visual and auditory information processing systems

Because it is nearly impossible to safely operate a vehicle with a 0.15% BAC, in Texas you can be charged with a Class A misdemeanor DWI if you drink and drive with this level of BAC.

A Few Quick Disclaimers

The number of drinks listed for each BAC level above is based on the approximate amount of alcoholic beverages that a 160-pound man would need to consume in a one hour period to reach that BAC. Due to the variety of factors that can impact your BAC, the numbers of drinks listed are estimates and should not be used to determine any specific person’s BAC on any specific occasion.

Additionally, the number of drinks listed for each BAC level is based on a standard drink, which is equal to the amount of an alcoholic beverage that is necessary to contain the equivalent 14.0 grams (0.6 ounces) of pure alcohol. This amount of pure alcohol can be found in the “standard drinks”:

  • 12 oz. beer (usually about 5% alcohol)
  • 8 oz. malt liquor (usually about 7% alcohol)
  • 5 oz. wine (usually about 12% alcohol)
  • 1.5 oz. or a “shot” of 80-proof liquor (usually about 40% alcohol)