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Drowsy Driving vs. Drunk Driving


*Nothing in this article constitutes medical advice. Seek the guidance of a physician if you have any questions.*


Since their invention in the late 19th century, cars have made modern life much easier. Unfortunately, they are also deadly. Each year in the United States, roughly 37,000 people die in motor vehicle accidents. Unfortunately, many of these incidents involve impaired drivers. Let’s take a look at the differences and similarities between drunk and drowsy driving.

What Is Drunk Driving?

Simply, drunk driving is the act of operating a motor vehicle (or motorcycle) under the influence of alcohol. “Drunk” in its everyday usage is a fairly subjective term, so states have defined this word for legal purposes. In all 50 states, having a blood alcohol concentration (BAC) of greater than .08 g/dL (grams per deciliter).

Being caught driving with a BAC in excess of .08 is usually considered “driving under the influence,” or DUI. The exact terminology can vary from state to state. Some jurisdictions use “driving while intoxicated” (DWI) or “driving while ability impaired” (DWAI). Let’s take a look at some drunk driving statistics:

  • In 2016, 10,497 people died in alcohol-impaired crashes. This equates to about 30 people per day
  • 28% of all traffic-related fatalities involved alcohol in 2016
  • In 2016, roughly 1 million people were arrested for impaired driving. Unfortunately, this is less than 1% of all self-reported incidents
  • While the average cost of a first time DUI varies, the sum total of fines, court fees, attorney fees, and all other associated costs ranges from $10,000-25,000
  • Entry into Canada is illegal until five years post-sentencing completion after a DUI
  • Fees, fines, and loss of driving privileges will almost certainly increase with a second or third offense

Effects of Drunk Driving

Similar to the loose definition of “drunk,” many people report different symptoms associated with drunkenness. Let’s take a look at what different BAC levels typically mean for different individuals. Keep in mind that these are simply guidelines, and every person may consume a different amount of alcohol that will result in different BACs.

  • 02: This is typically the minimum BAC that people report feeling any signs of intoxication. Individuals report mild mood alterations, slight body warmth, and altered mood. Visual functioning will start to decrease, leading to a lessened ability to track rapidly moving objects.
  • 05: This BAC may correspond to “drunk” for some people. Symptoms may include happy mood, impaired judgment, and loss of small-muscle control like eye focusing. This leads to impaired muscle control and slower reaction times.
  • 08: This level of intoxication is typically obvious to observers. Muscle coordination may become extremely poor in regards to balance, vision, speech, hearing, and reaction time. This is also when memory and concentration begin to decline. This can make driving very difficult.
  • 10: For most people, this BAC corresponds to clear drunkenness. Individuals may find walking and speaking normally difficult. Individuals who are driving may find it difficult to notice traffic signals, pedestrians, and other cars.

Physiology of Drunk Driving

Now that we understand how alcohol may affect driving ability, let’s take a look at the biology of how these effects occur.


First, the alcohol in a beverage must be absorbed in the stomach. Absorption rates vary from person to person and generally depend on a few factors. Drinking on an empty stomach, for example, does in fact increase the rate of absorption. But, this phenomenon is more noticeably observed when the alcohol concentration of the drink is middling, such as 20-30%. Spirits that typically contain alcohol in excess of 40% will delay gastric emptying and thus slow absorption.

Brain Effects

Alcohol is a known central nervous system depressant. Predominantly, alcohol functions by increasing the concentration of the neurotransmitter γ-aminobutyric acid, also known as GABA. Generally speaking, GABA slows down, or inhibits, the activity of neurons that it interacts with. This explains some of alcohol’s effects: loss of motor skills, slurred speech, and impaired memory. Additionally, the pleasurable effects of alcohol are due to an increase in dopamine, a reward neurotransmitter.

What Defines Drowsy Driving?

The definition of drowsy driving is a bit more complicated to nail down. The Centers for Disease Control defines drowsy driving as “operating a motor vehicle while fatigued or sleepy.” Here are some facts about drowsy driving:

  • The National Highway Traffic Safety Administration estimates that, on a yearly basis, drowsy driving causes 83,000 crashes, 37,000 injury crashes, and 886 fatal crashes.
  • Roughly 1 out of 25 adults, 18 years and older, reported falling asleep while driving in the past 30 days.
  • People who snored and those who slept 6 hours or less per day are more likely to fall asleep while driving
  • There are many warning signs that you may be too drowsy to drive, such as yawning or blinking frequently, drifting from the lane, having difficulty remembering driving the last several miles, hitting a rumble strip, or missing exits
  • Many, many people are prone to drowsy driving, such as individuals who do not get enough sleep, commercial drivers, shift workers, drivers with untreated sleep disorders like sleep apnea

Physiology of Drowsy Driving

The biology of drowsy driving can be rather complicated. In a nutshell, being drowsy affects people while driving the same way it affects them during other tasks - it slows us down. Similar to alcohol, sleep deprivation slows the central nervous system. Here are a few of the things a drowsy driver may experience:

  • Slows reaction times
  • Decreased ability to pay attention to the road
  • Decision-making skills and speed lessened

Drowsy & Drunk Driving

So, then, how do drunk and drowsy driving compare? First, they are both dangerous, destructive, and reckless. Combined, they account for roughly 12,000 deaths a year. The Centers for Disease Controls notes that “studies have shown that going too long without sleep can impair your ability to drive the same way as drinking too much alcohol.” They go on to provide comparisons between various levels of drowsy and their equivalent BAC.

  • Being constantly awake for 18 hours is roughly equivalent to driving with a blood alcohol concentration of 0.05.
  • Being constantly awake for 24 hours is roughly equivalent to driving with a blood alcohol concentration of 0.10. This would be an illegal BAC in all 50 states

In short, drowsy driving can be just as dangerous as drunk driving. Both should be avoided, and if you think you may have a sleep disorder, contact your physician.


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Written by: Patrick O'Hare


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