How Alcohol Affects Driving Ability

Driving under the influence of alcohol can impair one’s hearing and vision significantly. It clouds one’s thinking, concentration, reasoning, hand-eye coordination, and response times, particularly in the face of unsafe driving conditions and hazardous situations.

The more alcohol enters a person’s system, the greater its negative impacts on the central nervous system. The measure for blood alcohol content is referred to as BAC or blood alcohol concentration.

A BAC of .08 grams of alcohol per deciliter (g/dL) of blood increases the risk of a DUI-related car accident exponentially — which is why it’s illegal to drive with this BAC (or higher) in all 50 states, plus the District of Columbia and Puerto Rico. In Utah, however, the BAC limit is set at .05 grams of alcohol per deciliter (g/dL) of blood.

In general, drinking alcohol while driving and drunk driving are forbidden because even smaller amounts of alcohol can impact a person’s ability to drive. In fact, back in 2018, NHTSA data revealed that there were 1,878 fatalities in car crashes involving drivers with BACs of .01 to .07 g/dL.

The Effects of BAC (Blood Alcohol Concentration)

According to the NHTSA, the effects of the various BAC levels on people are as follows:

• 0.02: The person becomes relaxed, feels slightly warm, and experiences a difference in their mood. There is a certain level of loss of judgment and a decline in their visual functions and ability to do two things at the same time.
• 0.05: The person exhibits exaggerated behavior, loss of or reduction in coordination and small-muscle control. They experience a generally pleasant or good feeling (being in the mood) and become less inhibited, although their judgment becomes impaired and they have a lower sense of alertness. 
• 0.08: The driver manifests poor muscle coordination, slurred speech, slow reaction time, and a reduced ability to detect danger. Vision, concentration, judgment, self-control, reasoning, perception, and memory are all impaired.
• 0.10: A driver with this BAC shows signs of deteriorated reaction time, lack of control, slow perception, impaired judgment, and poor coordination. They may no longer be able to keep to the right lane and brake properly.
• 0.15: With this BAC, there is significant loss of muscle control and balance, inattentiveness to their driving task, and difficulty maintaining vehicle control.

The effects of alcohol may also vary, depending on the level of alcohol tolerance of each person.

Dangers of Drinking and Driving

As indicated in the various deleterious effects of different BAC levels on people, the dangers of drinking and driving are real and could lead to fatal lapses in judgment.

In general, the physiological effects of driving under the influence of alcohol are as follows:

Slow Reaction Time

The presence of alcohol in the body affects how fast (or how slowly) you can respond to various stimuli. When you’re driving under the influence of alcohol, your reaction time is usually slower and you may not notice changing traffic or driver’s signals. This, of course, is a recipe for disaster.

Lack of Coordination

For you to be able to do anything — especially drive — your hands, eyes, and legs should be working in coordination. The presence of alcohol in your body, especially after heavy drinking, can lead you to exhibit uncoordinated movements, such as when you’re walking, opening the car door, or finding the ignition. This means you’re in no condition to drive.

Poor Judgement

How you react or choose to act in certain situations depends on how your brain interprets and processes information. However, when your thought processes are impaired by alcohol, you may exhibit poor judgment. Your brain won’t have the alertness and focus it needs to help you respond to unsafe driving situations promptly, such as when you need to slow down quickly or swerve to avoid a collision.