Signs & Symptoms Of Alcohol Impairment

Driving under the influence of alcohol or drugs is always a bad idea. The consequences are severe and long lasting. Not only will being prosecuted for and possibly being convicted of a DUI affect a driving record and privileges, but it can have a significant impact on your emotional state, your relationships with family and friends, and your connection to society. In this section, we will examine what constitutes a DUI offense and its potential consequences and effects.

Every year thousands of Texans mix alcohol or other drugs with driving and experience injury, death, damage to property, legal costs, increased insurance premiums, treatment costs, loss of driving privileges, fines, and incarceration.

Previously, you, or someone you know may have made choices that led to drinking and driving. If so, our goal would be to help you make better decisions that can avoid the serious consequences of a DWI.

Stats reveal in the United States millions of adults over the age of 21 use alcohol on and for several occasions. For many, alcohol use is socially acceptable and complements social events, food, and conversation with friends and family. For some families the consumption of wine or other alcoholic beverages are part of their heritage. Some simply enjoy the relaxing effects of drinking or like the taste of a beer or a glass of wine with a meal of their liking. In these cases, the use of alcohol is moderate, occasional, and low-risk. Most drinking drivers are social drinkers who violate the law only on rare occasions. Drinking alcohol, then driving is never a good idea. We highly discourage even one drink before getting behind the wheel.

A large number of people choose not to drink. They enjoy the benefit from choosing to abstain from alcohol use. Abstinence is a lifesaving decision for people recovering from chemical dependency. For those who abstain, there is no risk of developing a dependency or experiencing other problems related to alcohol use such as a drinking and driving violation. For those people with a family history of alcoholism, a choice to remain abstinent will help break the cycle of addiction.

There are benefits from the safe and low-risk use of alcohol or the choice to abstain. Alcohol is the number one factor in deaths and injuries on our highways every year claiming hundreds and thousands of victims across the country.

At intoxicating levels alcohol is the most abused substance we know today. Drivers with alcohol present in their systems have the highest crash responsibility rates. Other drugs have been found in a notable percentage of fatalities.

Research conducted over the past 20 years shows it’s generally accepted that approximately 38% of all traffic deaths are caused by driving under the influence of alcohol. Drugs appear to have the highest potential for hazards when mixed with alcohol. 

Fatality Risk for Drivers in Single Vehicle Crashes at Various Alcohol Concentration (AC) Levels: Relative to Non-Drinking Drivers are as follows:

BAC LEVEL FATALITY RISK –   Source: Zadora Study

0.05% – 0.09%

11 times greater

0.10% – 0.14%

48 times greater

0.15% or higher

380 times greater

There are five classifications of controlled substances (drugs) that are defined in the Controlled Substances Act of 1970. 

  • opium and its derivatives 

  • hallucinogens

  • depressants

  • stimulants

Note: These classes cover a range of drugs, from heroin and LSD to over-the-counter cough syrups containing codeine. 

Please be responsible and consult your Doctor if you are unable to discern the dangers of over the counter medications and any prescription medications you are taking.  

How The Body Absorbs And Distributes Alcohol

After alcohol is consumed it goes from the stomach and intestines and is absorbed short thereafter into the bloodstream. As it circulates in the bloodstream, alcohol distributes itself evenly throughout all the water in the body’s tissues and fluids.

Source: addictionblog.org

When ingested, alcohol passes from the stomach into the small intestine, where it is rapidly absorbed into the blood and distributed throughout the body. Because it is distributed so quickly and thoroughly the alcohol can affect the central nervous system even in small concentrations. In low concentrations, alcohol reduces inhibitions. As blood alcohol concentration increases, a person’s response to stimuli decreases markedly, speech becomes slurred, and he or she becomes unsteady and has trouble walking.

Due to the way alcohol distributes itself throughout the body fluids and tissue it can be measured by testing the urine, saliva, or water vapor in an individual’s breath, or by testing one's blood. Law enforcement agencies typically use breath testing methodology, but often convert breath test results to equivalent blood alcohol measurements because early drunk driving laws based their limits on blood tests (National Highway Traffic Safety Administration [NHTSA] 1990). In cases of alcohol–related traffic fatalities, however, blood testing must be used to estimate alcohol levels.

To calculate BAC, the amount of alcohol in the bloodstream is measured in milligrams (mg) of alcohol per 100 milliliters (ml) of blood. It is usually expressed as a decimal such as 0.08 or 0.15. For example, a BAC of 0.10% means that an individual’s blood supply contains one part alcohol for every 1,000 parts blood.

Alcohol And It’s Breakdown In The Human Body

After you swallow an alcoholic drink, about 25 percent of the alcohol is absorbed straight from your stomach into the bloodstream. The rest is mostly absorbed from your small bowel. How quickly you absorb alcohol depends on several factors, including:

  • the concentration of alcohol in your drink (drinks with a higher alcohol concentration are generally absorbed faster);

  • whether your drink is carbonated (champagne, for example, is absorbed more quickly than non-sparkling drinks); and

  • whether your stomach is full or empty (food slows down the absorption of alcohol).

Once alcohol has entered your bloodstream it remains in your body until it is processed. About 90-98 percent of alcohol that you drink is broken down in your liver. The other 2-10 percent of alcohol is removed in your urine, breathed out through your lungs or excreted in your sweat.

The average person will take about an hour to process 10 grams of alcohol, which is the amount of alcohol in a standard drink. So if you drink alcohol faster than your body can process it, your blood alcohol level will continue to rise.

Crash Risk As A Consequence

Legal intoxication level most states have adopted is a Blood Alcohol Concentration (BAC) of 0.08.

Several scientific studies have identified how the physiologic responses needed to drive safely become impacted by alcohol at a BAC level of 0.08 percent or lower. Experimental laboratory studies have reported on the physical deficits experienced with a 0.08 percent BAC, a level reached by a 170 lb male after consuming four drinks in 1 hour on an empty stomach, or by a 135 lb female consuming three drinks. These deficits include, but are not limited to:

  • Impaired and reduced peripheral vision 

  • Deficient recovery from glare

  • Impaired performance in complex visual tracking

  • Reduction in divided attention performance (example: the concurrent performance of two or more tasks such as number monitoring, tracking, visual search, and detection of auditory stimulus).

Another interesting study conducted in a comparison of alcohol test results, Source: (Zador) discovered that for every 0.02% increase in a driver’s BAC, this nearly doubled a person’s risk of being involved in a single vehicle fatal accident. This particular study focused on alcohol test results of drivers killed in single vehicle fatal accidents, then compared them with breath alcohol samples collected by 2,850 drivers pulled over in the same States as part of a National roadside survey of drivers. To duplicate driver fatalities to the roadside breath testing subjection, time of incident, days, and roadway types were confined to those used in the survey of drivers. It concluded that, for all age and gender groupings, the likelihood of being fatally injured driver was AT LEAST 9 times greater when BAC levels were at 0.05 to 0.09 percent vs. zero (0) BAC. For every 0.02% increase in BAC. For females and drivers under the age of 21 the risk increased substantially more.

Effects Of Alcohol On Driving Skills

Driving and drinking alcohol do not go together. When you drive, you need your eyes, hands, and feet to control the vehicle. You also need your brain to control your eyes, hands, and feet. Driving involves a rapidly changing environment, and you must be aware, alert, and able to make quick decisions at all times.

Impaired drivers are dangerous, but driving can also become dangerous and even fatal when drinking alcohol. Drinking can negatively affect any or all of these crucial driving skills.

How Alcohol Affects Your Judgment

Alcohol typically affects the body in a particular sequence. The first part of your body that alcohol affects is the brain, particularly your judgment. This means that your ability to think clearly, reason, plan ahead, and make sound decisions is reduced, even with BAC levels lower than .02 percent.


Even small amounts of alcohol can impair your ability to concentrate on the many tasks that driving entails, and instead leaves you concentrating on only one action.

Unfortunately, when driving you need to focus on several things at once, such as your vehicle position, speed, and other traffic on the road. As soon as you stop focusing on the road, a collision can happen. Many traffic accidents result from a drunk driver who is distracted or who has a short attention span.


Alcohol can impair your ability to control eye movement and see clearly. It can slow down your eye muscle function and reduce peripheral vision. Studies show that drunk drivers tend to focus on a single point for a long time, and are thus less aware of crucial peripheral areas. Alcohol can also negatively affect your ability to judge depth and distance. You may also find yourself driving with blurred vision, or with impaired color perception and night vision.

Reaction Time

Alcohol can slow down your reflexes and decrease the ability to understand and react immediately to changing situations. Studies show that drivers under the influence of alcohol are unable to respond to stimuli as quickly as when they are sober. Due to your impaired comprehension and coordination, your reaction time may slow down by as much as 15 to 25 percent. A decreased reaction time may result in accidents and collisions involving injuries or fatalities.


Steering is a key skill we need while driving. It becomes significantly  impaired with alcohol concentration levels as low as .05%. The majority of experienced drivers confirm steering is relatively simple, however keeping a vehicle in the correct lane and direction may become difficult when the driver has been drinking. Impaired drivers often oversteer, resulting in weaving, swerving, braking for no reason, etc.

You’ve probably “heard” that alcohol impaired drivers are at less risk for injury when involved in a collision because they are relaxed. Despite this, more recent studies conclude that alcohol actually increases the likelihood and severity of injury.

How Alcohol Affects Perception

Alcohol can impair your ability to control eye movement and see clearly. It can slow down your eye muscle function and reduce peripheral vision, Studies show that drunk drivers tend to focus on a single point for a long time, and are thus less aware of crucial peripheral areas. Alcohol can also negatively affect your ability to judge depth and distance. You may also find yourself driving with blurred vision, or with impaired color perception and night vision.

How Alcohol Affects Comprehension & Attention

Drinking can affect your ability to properly understand or interpret road signs, signals, and situations that you need to respond quickly in order to be safe on the road. Alcohol may leave you easily confused or unable to respond in an emergency situation.

Any alcohol use resulting in even very low alcohol concentrations (.02) can reduce a person’s ability to pay attention to more than one thing at a time. Driving a vehicle requires that the driver divide attention between steering the car in the correct direction and lane, as well as keeping track of other vehicles, traffic signals, pedestrians, and other events. These tasks occur at the same time, so the driver must divide attention between them. If impaired by alcohol, drivers will tend to focus attention only on steering the car correctly and miss other important information that can increase the risk of a crash. 

Alcohol's Effect On Coordination

The part of the brain that is associated with coordination becomes less active under the influence of alcohol. A brain with alcohol in the system has poorer balance, hand-eye coordination, and reaction time than when compared to brains without alcohol. Alcohol also has the effect of making someone drowsy or sleepy. When a person is under the influence of alcohol hand-eye coordination is impaired. The ability to grab, squeeze or time a movement may be difficult to perform.

Alcohol's Effect On Your Balance

One of the effects of drinking alcohol is called “the spins”. This is typically a side effect that many people experience after they binge drink alcohol. This condition, usually referred to as dizziness, can cover two different experiences:

  • lightheadedness or feeling like one is about to pass out.

  • vertigo or a sense of motion when not moving.

Alcohol dizziness is more associated with vertigo than lightheadedness, although this type of dizziness can also occur. During a Field Sobriety Test an officer will have the driver walk on a straight line. This can be difficult to successfully execute with even small amounts of alcohol in the bloodstream.

Symptoms Of Alcohol Impairment

The level of impairment related to alcohol consumption is directly affected by the amount consumed and ingested. The clinical symptoms of alcohol impairment vary in accordance with the concentration of alcohol in the bloodstream (BAC). In typical cases the relationship between a person’s blood alcohol concentration and the level of impairment symptoms they experience are noted below in BAC percentages:

BAC .01 – .05: The person will experience very little behavioral differences when compared to a sober person.

BAC .03 -.12: The person will experience the onset of mild euphoria, typically accompanied by being more talkative and social. By this point, the person will experience reduced inhibitions, and their confidence may increase. Sensory and motor impairment is likely to begin, while judgment and control faculties are reduced.

BAC .09 – .25: The person may experience some emotional instability. Their ability to accurately perceive, remember, or understand something is likely to be reduced. Reaction time is increased, hand eye coordination is affected, balance is difficult to sustain and they may become sleepy or sluggish.

BAC .18 – .30: The person may experience loss of orientation, confusion may set in, dizziness and possibly more instability of emotion. The pain threshold is increased and the ability to walk in a straight line is very difficult. Speech is slurred and loss of muscular control is common. Vision is substantially impaired and perception of shape, color, size and movement become difficult, if not impossible.

BAC .25 – .40: The person will barely be able to respond to most stimuli, likely NOT be unable to walk or stand at all, vomiting and incontinence may occur. Consciousness may be lost. Immobility is likely the last phase.

BAC .35 – .50: The person is likely completely unconscious exhibiting little or no reflexes. Circulation and respiration will be impaired. Body temperature will decrease. The person will become incontinent. 

BAC .45+: This is where the person is likely to die. It’s possible the respiratory system will fail.

Blood Alcohol Content (BAC) And How It’s Measured

BAC stands for Blood Alcohol Concentration. It is measured as mass per volume, which means it determines how many grams of alcohol are present in 100 milliliters of blood. A BAC of .01% means that there are .01 grams of alcohol per 100 grams of an individual’s blood, or .1 grams of alcohol per 1000 grams of blood. In some countries, BAC is measured in grams per liter of blood (g/L).

For instance, a BAC of 0.10% means that a person has one part alcohol per 1,000 parts blood in the body. The maximum limit allowed by your system while driving is .08%.

Alcohol concentration in the blood depends on several factors:

  • Gender

  • Body weight

  • How quickly the alcohol was consumed

  • When the last sip was taken; and

  • If the driver was drinking on an empty stomach.

It doesn’t make any difference whether you drink beer, wine, or liquor. Standard servings of each have the same amount of alcohol. A 12-ounce glass of 5% beer has one ounce of pure alcohol, as does a five-ounce glass of 12% wine or 1.5 ounces of 80-proof liquor. On average, the human body can dispose of a 12-ounce beer in about one hour.

Scientists were eager to find a chemically based method of determining an individual’s level of intoxication for two reasons. First, it would allow for drunk driving charges to be assigned on an objective basis, rather than relying on the subjective analysis of a law enforcement official. Second, due to differences in our individual physiologies and alcohol tolerance, BAC is a much more accurate measure of intoxication than the number of drinks consumed.

As a general rule, the consumption of two beverages containing 20 grams of alcohol will raise the BAC of the average individual to approximately .05%. If a single beverage containing 20 grams of alcohol is consumed every hour after the first two, the BAC will remain at a level of .05%.

While BAC does determine the level of an individual’s intoxication from a chemical perspective, it does not necessarily determine a person’s level of impairment. Alcohol tolerance varies widely among individuals and is affected by age, gender, genetics, adaptation, and the effects of other simultaneous intoxicants.

Unless a person’s tolerance is very high, a BAC of .2% means the person is seriously intoxicated while a BAC of .35% indicates alcohol poisoning, which could be fatal.

The measurement of an individual’s blood alcohol concentration is not a perfect science. For one, breath analysis tests assume that the alcohol has already been absorbed and distributed throughout the body. If alcohol has been consumed very recently, then the BAC will report a lower percentage.

How To Spot A Drunk Driver

Here are a few signs that a fellow motorist may be driving while impaired:

  1. Quick acceleration or deceleration

  2. Tailgating

  3. Weaving or zig-zagging across the road

  4. Driving anywhere other than on a road designated for vehicles

  5. Almost striking an object, curb, or vehicle

  6. Stopping without cause or erratic braking

  7. Drifting in and out of traffic lanes

  8. Signaling that is inconsistent with driving actions

  9. Slow response to traffic signals (e.g. sudden stop or delayed start)

  10. Straddling the center lane marker

  11. Driving with headlights off at night

  12. Swerving

  13. Driving slower than 10 mph below the speed limit

  14. Turning abruptly or illegally

  15. Driving into opposing traffic on the wrong side of the road

Helpful Hints to avoid a dangerous situation:

  • When in front of an impaired driver, move to your right and let them pass. 

  • If an impaired driver is in front of you, stay a safe distance behind allowing time to react.

  • If an impaired driver is coming toward you, slow down, move to the right and stop safely. 

  • Once you are a safe distance from the impaired driver, call 9-1-1 or the police. 

  • Never attempt to stop or guide the impaired person’s vehicle.

How To Make Low Risk Choices

Drinking alcohol is a personal decision. Ultimately you are responsible for the consequences of your decision(s). In order to reduce exposure to the negative consequences of drinking and driving, you may want to consider setting guidelines and rules for your alcohol use and consumption. 

Decisions about using or abstaining from alcohol should be based on a set of personal guidelines and rules that may enhance your health and reduce your risk of experiencing alcohol related negative consequences. You may want to establish your guidelines and adhere to them in a manner you deem responsible. This acronym below may help you do this. Consider using extreme caution when consuming alcohol under the following circumstances

The word HALT has been helpful in establishing guidelines for when the use of alcohol is unhealthy, dangerous, or inappropriate. A person should be extremely careful or avoid using alcohol when: