How Alcohol Affects Driving Ability

How deadly is DWI / DUI? Here are a few drinking and driving facts + internet memes. Drinking and driving is dangerous; it leads to an estimated 32% of fatal car accidents every year, according to the National Highway Traffic Safety Administration (NHTSA)

Why is drinking alcohol and driving so hazardous? As you may have heard, alcohol is a depressant. But don’t think of ‘depressant’ always as ‘makes you depressed.’

6 Effects of Drinking and Driving

Alcohol is called a depressant because it depresses the functions of our central nervous system.

Normal functions of the brain are delayed, which affects:

  • Information processing (cognitive) skills
  • Hand eye coordination (psychomotor) skills

Impaired thinking ability + impaired ability to react + driving = ACCIDENTS

Driving While Intoxicated – The Science

But what’s the scientific basis? Research indicates that the effects on the prefrontal cortex and temporal cortex of the brain are particularly acute when people drink. Decreased activity in these areas affects the ability to make good decisions, and it also affects the ability to think rationally. Additionally, alcohol consumption decreases activity in the cerebellum, which is critical for coordinating psycho-motor activity.

Poor cognitive and psycho-motor skills lead to degradation in these driving skills:

#1 Judgment


The first effect that alcohol has is on your mental functions. Judgment is the first out the window. Reason and caution drop, and you may take terrible risks that endanger lives. This can occur when your blood alcohol content (BAC) is just .02%.

#2 Concentration

Driving safely requires the ability to shift attention from one thing to another quickly. Alcohol reduces your ability to concentrate on vital driving tasks that come fast when you are moving:

  • Vehicle position
  • Vehicle speed
  • Watching for other traffic
  • Adjusting the radio
  • Talking to passengers

Drinking and driving makes you more likely to concentrate on one thing.

#3 Comprehension

Drinking affects the ability to interpret signs, situations and signals. You have to be able to understand these quickly to drive safely. A drunk driver can fail to respond to traffic slowing ahead, or blow through a stop sign.

#4 Coordination

After your thinking is affected, next are your motor skills.  A drunk driver will have difficulty with everything from putting the key in the ignition, to actually getting into the car. Further, loss of coordination greatly slows reaction time.

#5 Vision and Hearing

Alcohol can reduce your visual acuity by 1/3. It also can affect peripheral vision so that you cannot see in your blind spots. It also affects your depth perception and judgment of distances to objects (other cars, people) can be compromised. Pupil reactions slow, and can lead to being blinded by oncoming headlights.

Ability to hear also is reduced and can muffle sounds, including sirens and car horns.

#6 Reaction Time

Alcohol increases the time to see and understand a situation, and then act. Reaction times can be slowed by as much as 25%. This leads to severe accidents that may have been easily avoided when sober.

Don’t Drink and Drive

The scientific facts behind alcohol’s effects are clear. Drinking leads to a degradation of skills vital to driving safely. No one should drive after they have had anything to drink. One drink – even if it leads to a BAC of less than the legally drunk standard of .08% – can affect one’s driving ability.

Dan Gordon is a DWI Criminal Defense Lawyer in Dallas, Tx. Call (469) 718-2020 to speak to a Tx DWI Attorney. Read our DWI Reviews article or checkout our post about DUI Lawyer Fees.