Photo: Stephen Leonardi, Pexels
Alcohol starts to affect your driving from the first drink, well before you feel drunk. At a blood alcohol concentration (BAC) of just 0.02%, NHTSA says your visual tracking and your ability to handle two tasks at once already decline. By 0.05% steering, coordination and emergency responses suffer. Once alcohol is in your blood, only time removes it. The rate differs from person to person, so there is no drink-per-hour countdown that tells you when you are safe or legal to drive. Coffee, food, exercise and cold showers don’t speed it up.
What counts as one standard drink in the US?
The CDC defines a US standard drink as 0.6 ounces (14 grams) of pure alcohol. That is about:
| Drink | Size | Typical strength |
|---|---|---|
| Beer | 12 ounces | 5% alcohol |
| Malt liquor | 8 ounces | 7% alcohol |
| Wine | 5 ounces | 12% alcohol |
| Distilled spirits (vodka, rum, whiskey) | 1.5 ounces | 40% (80 proof) |
A serving that is bigger or stronger than these counts as more than one drink, so a large glass of wine or a strong beer can easily be two. Louisiana and Alabama both make the same point: beer, wine or whiskey, it’s the amount of alcohol that reaches your blood that counts.
How BAC rises
Alcohol goes from your stomach and small intestine into your bloodstream. Louisiana says it reaches your brain in about 20 minutes, and NHTSA says it can be measured within 30 to 70 minutes of a drink. How high your BAC goes depends on:
- How many drinks you have.
- How fast you drink them. Drinking quickly gives a higher peak.
- Body weight. More body water dilutes the alcohol.
- Sex. NHTSA notes women generally reach a higher BAC from the same amount.
- Food in your stomach. This slows absorption, so the same drinks hit harder on an empty stomach.
Because so many factors are involved, NHTSA says it is very hard to judge your own BAC. Feeling “fine” tells you nothing. Not noticing that you’re impaired is itself a sign of impairment.
How BAC affects your driving, level by level
NHTSA’s table shows the BAC at which each effect usually first appears:
| BAC | Typical effects | Effects on driving |
|---|---|---|
| 0.02% | Some loss of judgment, relaxation, altered mood | Decline in visual tracking of moving targets; harder to do two things at once |
| 0.05% | Impaired judgment, lowered alertness, loss of inhibition, less control of small muscles such as focusing your eyes | Reduced coordination, harder to track moving objects, difficulty steering, slower response to emergencies |
| 0.08% | Poor muscle coordination (balance, vision, reaction time, hearing); harder to detect danger | Poor concentration and speed control, short-term memory loss, slower processing of signals and hazards |
| 0.10% | Clearly slower reactions, slurred speech | Trouble keeping lane position and braking appropriately |
| 0.15% | Far less muscle control, major loss of balance | Substantial impairment in vehicle control and attention |
The Louisiana guide adds the effects drivers notice least: alcohol makes you take risks, forget routine tasks such as signaling or turning on headlights, misjudge speed and distance, and get angrier at other drivers. It also blunts your ability to judge your own condition.
How fast does alcohol leave your body?
Your liver does most of the work, and nothing you do speeds it up. How fast it goes varies from person to person, depending on things like your genes, how much you drink and your diet. Driver guides quote average rates, but yours may be slower, so you cannot count hours to work out when you are safe or legal to drive.
That is why “morning after” driving is a real risk. A late night out can leave you over the limit for the drive to school or work. If there is any doubt, get a lift, take a taxi or use public transport.
Myths that don’t sober you up
| Myth | What the handbooks say |
|---|---|
| Black coffee | May make you feel more awake but won’t sober you (Alabama, Louisiana). You become a wide-awake impaired driver. |
| Cold shower or exercise | No effect on BAC (Louisiana, Alabama). |
| Eating | Food eaten before or while drinking slows absorption, but once alcohol is in your blood, food doesn’t remove it (Alabama, NHTSA). |
| “Beer is weaker than liquor” | A standard beer and a standard shot hold about the same alcohol (CDC, NHTSA). |
| “I feel fine” | Impairment starts with the first drink (Kentucky). You will likely be too impaired to drive before you feel drunk (NHTSA). |
The legal limits, briefly
- Drivers 21 and over: 0.08% is the adult limit in most states; check your own state’s figure. You can still be arrested below it if your driving shows impairment (NHTSA, Oregon, California).
- Drivers under 21: zero tolerance in every state. California sets 0.01%, Louisiana 0.02%, and Oregon says any amount. Texas DPS says any detectable amount is a criminal offense for a minor driving. Details in zero tolerance laws for drivers under 21.
- Refusing a test: implied consent laws mean a refusal leads to license suspension. See implied consent and DUI in the US.
Mixing alcohol with cannabis or medicines makes impairment worse. See drugged driving and cannabis and prescription and over-the-counter medicines.
Plan before you drink
- Choose a designated driver who isn’t drinking at all (NHTSA).
- Arrange ahead of time to stay over, or take a taxi or ride home (NHTSA).
- Never ride with a driver who has been drinking, and don’t let a friend drive after drinking (Kentucky, Louisiana).
For how licensing works in each state, start with learning to drive in the USA.
Sources
- National Highway Traffic Safety Administration, “The ABCs of BAC” (DOT HS 809 844) (nhtsa.gov)
- Centers for Disease Control and Prevention, “About Standard Drink Sizes” (cdc.gov)
- Louisiana Office of Motor Vehicles, “Class D & E Driver’s Guide” (DPSMV 2052, R08/25), Alcohol and Blood Alcohol Concentration (public.powerdms.com)
- Alabama Law Enforcement Agency, “Alabama Driver Manual”, Chapter 4: The Driver (alea.gov)
- Kentucky State Police, “Kentucky Driver Manual” (updated July 2026), Alcohol, Other Drugs and Driving (kentuckystatepolice.ky.gov)
- California DMV, “California Driver’s Handbook, Section 9: Alcohol and Drugs” (dmv.ca.gov)
- Oregon DMV, “Oregon Driver Manual: Safe and Responsible Driving, Impaired Driving” (oregon.gov)
- Texas Department of Public Safety, “Alcohol-Related Offenses” (dps.texas.gov)
- National Institute on Alcohol Abuse and Alcoholism, “Alcohol Metabolism” (niaaa.nih.gov)