Drinking and driving means operating a motor vehicle after consuming enough alcohol to impair your ability to drive safely. In 2023, alcohol-impaired driving killed 12,429 people in the United States, accounting for 30 percent of all traffic fatalities that year. Every state makes it illegal to drive above a set blood alcohol concentration (BAC), but impairment begins well before you hit that legal threshold.
How Alcohol Impairs Your Driving
Alcohol is a central nervous system depressant, and it starts affecting the skills you need behind the wheel after just one or two drinks. A 160-pound man who has two alcoholic beverages will already experience some loss of judgment, a reduced ability to track moving objects, and weaker multitasking. These are exactly the skills driving demands every second you’re on the road.
At a BAC of 0.05%, your alertness drops, your judgment becomes unreliable, and your ability to quickly focus your eyes deteriorates. Steering gets harder, and your response to sudden emergencies slows noticeably. By the time you reach 0.08%, the legal limit in most states, your muscle coordination is reduced, your reasoning is impaired, and your reaction time has slowed by an average of 120 milliseconds. That tenth of a second can be the difference between braking in time and a fatal collision.
What makes alcohol especially dangerous for drivers is that it undermines judgment first. You feel less inhibited and more confident in your abilities at the same time those abilities are declining. Most impaired drivers don’t believe they’re too drunk to drive, which is itself a symptom of impairment.
Legal BAC Limits
As of 2025, 49 states and Washington, D.C. set the legal BAC limit for adult drivers at 0.08%. Utah is the exception, with a stricter limit of 0.05%. On federal lands, the limit is 0.00%. The federal government incentivized these standards by tying highway funding to states adopting a 0.08% per se limit, starting in 2004.
For drivers under 21, the rules are far stricter. States enforce “zero tolerance” laws with BAC limits typically set at 0.02%, essentially criminalizing any detectable alcohol. In Georgia, for example, a driver under 21 caught with a BAC between 0.02% and 0.08% faces an automatic six-month license suspension and is ineligible for any limited driving permit. Commercial drivers are also held to lower thresholds, generally 0.04%.
It’s worth noting that “per se” laws mean you are legally impaired at or above the BAC limit, regardless of whether you appear sober. You can also be charged with impaired driving below the legal limit if an officer determines alcohol has affected your ability to operate a vehicle.
What Counts as a Standard Drink
People frequently underestimate how much alcohol they’ve consumed because drink sizes vary widely. In the United States, one standard drink contains 0.6 ounces (14 grams) of pure alcohol. That translates to:
- Beer: 12 ounces at 5% alcohol
- Malt liquor: 8 ounces at 7% alcohol
- Wine: 5 ounces at 12% alcohol
- Liquor: 1.5 ounces (one shot) at 40% alcohol
A large restaurant pour of wine can easily be two standard drinks. A strong craft beer at 9% ABV in a pint glass is nearly two drinks as well. If you’re estimating your intake based on “number of glasses,” you may be significantly underestimating your BAC.
How Your Body Processes Alcohol
Your body breaks down alcohol at a fixed rate of about 0.5 ounces of pure alcohol per hour, roughly equivalent to one standard drink. This rate doesn’t speed up if you drink water, eat food, or have coffee. Those things may help you feel more alert, but they don’t lower your BAC any faster.
Several factors influence how quickly your BAC rises in the first place: body weight, biological sex, how recently you ate, medications, and individual metabolism. Two people can drink the same amount and register very different BAC levels. The only thing that reliably brings your BAC down is time.
This is why “waiting it out” after a night of heavy drinking can be misleading. If your BAC peaks at 0.15% at midnight, you could still be above the legal limit at 7 or 8 a.m. the next morning. Many impaired driving arrests happen the morning after.
Legal Consequences of a DUI
The penalties for drinking and driving are serious even for a first offense and escalate steeply with each subsequent conviction. While specifics vary by state, a first DUI conviction typically results in a license suspension of up to 12 months, mandatory completion of an alcohol risk reduction program, and substantial reinstatement fees. In many states, refusing a breathalyzer test triggers an automatic one-year suspension that may disqualify you from getting even a limited permit.
Repeat offenses carry much harsher consequences. A second DUI within five years can result in an 18-month suspension, with the first 120 days being a “hard suspension” where no driving is permitted at all. A third offense can lead to a five-year license revocation and classification as a habitual violator, a designation that follows you for years and affects insurance rates, employment, and more.
Beyond the legal system, the financial cost of a DUI is substantial. Between legal fees, fines, increased insurance premiums, mandatory classes, and lost wages, a first-offense DUI can cost thousands of dollars over several years.
Ignition Interlocks and Prevention
One of the most effective tools for preventing repeat offenses is the ignition interlock device, a breathalyzer wired into a vehicle’s ignition system. The driver must blow into the device and register below a set BAC before the car will start. While these devices are installed, re-arrest rates for impaired driving drop by a median of 67%.
Many states now require interlock devices after a second DUI conviction, and some mandate them after a first offense. The driver typically pays for installation and monthly monitoring fees. Following a third conviction in states like Georgia, 12 months of interlock use is required before driving privileges can be fully restored.
The most reliable prevention, of course, is separating drinking from driving entirely. Rideshare services, designated drivers, and public transit eliminate the guesswork of estimating your own impairment, which, as the biology makes clear, is something alcohol makes you particularly bad at judging.