- Alcohol Effects
- Risk Factors
- Consequences
- Responsible Driving
How alcohol affects driving ability
Traffic Safety Facts & Data PublicationsAlcohol 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 2022, there were 2,337 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 |
Frequently Asked Questions
