Drunk Driving: How Alcohol Affects Driving Ability



Source: NHTSA

https://www.nhtsa.gov/risky-driving/drunk-driving


Alcohol is a substance that reduces the function of the brain, impairing thinking, reasoning and muscle coordination. All these abilities are essential to operating a vehicle safely.

As alcohol levels rise in a person’s system, the negative effects on the central nervous system increase. Alcohol is absorbed directly through the walls of the stomach and small intestine. Then it passes into the bloodstream where it accumulates until it is metabolized by the liver. A person's alcohol level is measured by the weight of the alcohol in a certain volume of blood. This is called Blood Alcohol Concentration, or BAC. At a BAC of .08 grams of alcohol per deciliter (g/dL) of blood, crash risk increases exponentially. Because of this risk, it’s illegal in all 50 states, the District of Columbia and Puerto Rico to drive with a BAC of .08 or higher, except in Utah where the BAC limit is .05.

However, even a small amount of alcohol can affect driving ability. In 2019, there were 1,775 people killed in alcohol-related crashes where a driver had a BAC of .01 to .07 g/dL. BAC is measured with a breathalyzer, a device that measures the amount of alcohol in a driver’s breath, or by a blood test.


The Effects of Blood Alcohol Concentration

BLOOD ALCOHOL CONCENTRATION (BAC) IN G/DL

TYPICAL EFFECTS

PREDICTABLE EFFECTS ON DRIVING

​.02

Some loss of judgment; relaxation, slight body warmth, altered mood

Decline in visual functions (rapid tracking of a moving target), decline in ability to perform two tasks at the same time (divided attention)

.05

Exaggerated behavior, may have loss of small-muscle control (e.g., focusing your eyes), impaired judgment, usually good feeling, lowered alertness, release of inhibition

Reduced coordination, reduced ability to track moving objects, difficulty steering, reduced response to emergency driving situations

.08

Muscle coordination becomes poor (e.g., balance, speech, vision, reaction time, and hearing), harder to detect danger; judgment, self-control, reasoning, and memory are impaired

Concentration, short-term memory loss, speed control, reduced information processing capability (e.g., signal detection, visual search), impaired perception

.10

​Clear deterioration of reaction time and control, slurred speech, poor coordination, and slowed thinking

Reduced ability to maintain lane position and brake appropriately

.15

Far less muscle control than normal, vomiting may occur (unless this level is reached slowly or a person has developed a tolerance for alcohol), major loss of balance

Substantial impairment in vehicle control, attention to driving task, and in necessary visual and auditory information processing


Risk Factors


Driving after drinking is deadly. Yet it still continues to happen across the United States. If you drive while impaired, you could get arrested, or worse — be involved in a traffic crash that causes serious injury or death.


Approximately one-third of all traffic crash fatalities in the United States involve drunk drivers (with BACs of .08 g/dL or higher). In 2019, there were 10,142 people killed in these preventable crashes. In fact, on average over the 10-year period from 2010-2019, more than 10,000 people died every year in drunk-driving crashes.


In every state, it’s illegal to drive drunk, yet one person was killed in a drunk-driving crash every 52 minutes in the United States in 2019.


Consequences


Driving a vehicle while impaired is a dangerous crime. Tough enforcement of drunk-driving laws has been a major factor in reducing drunk-driving deaths since the 1980s. Charges range from misdemeanors to felony offenses, and penalties for impaired driving can include driver’s license revocation, fines, and jail time. It’s also extremely expensive. A first-time offense can cost the driver upwards of $10,000 in fines and legal fees.


Many states require offenders to install ignition interlock devices at the driver’s own expense. An ignition interlock device is a breath test device connected to a vehicle’s ignition. The vehicle cannot be operated unless the driver blows into the interlock and has a BAC below a pre-set low limit, usually .02 g/dL. NHTSA strongly supports the expansion of ignition interlocks as a proven technology that keeps drunk drivers from getting behind the wheel.


Responsible behavior

BEING A RESPONSIBLE DRIVER IS SIMPLE: IF YOU ARE DRINKING, DO NOT DRIVE.


  1. Plan your safe ride home before you start the party, choose a non-drinking friend as a designated driver.

  2. If someone you know has been drinking, do not let that person get behind the wheel. Take their keys and help them arrange a sober ride home.

  3. If you drink, do not drive for any reason. Call a taxi, a ride-hailing service, or a sober friend.

  4. If you’re hosting a party where alcohol will be served, make sure all guests leave with a sober driver.

  5. Always wear your seat belt — it’s your best defense against impaired drivers.

If you see an impaired driver on the road, contact local law enforcement. Your actions could help save someone’s life.