Driving under the influence of drugs or alcohol is illegal throughout the United States. All 50 states consider a driver whose blood alcohol content is .08 percent or greater to be violating the law. Any U.S. commercial driver is subject to a DUI conviction if his or her BAC is .04 percent or more. In the case of drivers under 21 years of age, the law disallows any BAC whatsoever in keeping with a zero-tolerance policy.
An individual’s BAC depends upon factors such as gender, weight, the number of drinks and the time of consumption. According to a calculation created by the National Highway Traffic Safety Administration, a woman who weighs 120 pounds and has consumed three average drinks over a two-hour period probably has a BAC that is over the legal limit. A man who weighs 180 pounds consuming five drinks during the same period is likely to be over the legal BAC limit for driving.
Each state sets its own penalties for DUI, with 42 plus the District of 
Columbia mandating license confiscation for a first offense. Additionally, the majority of states institute harsher penalties for drivers with greater BACs. For example, Alaska, California, Washington, and many others impose additional sanctions for those who have BACs at .15 percent or higher. Florida, Massachusetts, and Tennessee are among the states with harsher penalties for drivers whose BACs are greater than .20 percent. These penalties include larger fines, the installation of ignition interlock devices or vehicle confiscation.
During a traffic stop, officers suspecting DUI use three methods to affirm or discount their suspicions. First, they observe the driver to detect evidence of alcohol or drug consumption. Signs include a distinctive smell, red and watery eyes, and affected speech. They may conduct a field sobriety test, in which they evaluate the driver’s balance and coordination. Based on the results of these two procedures, officers may elect to administer a Breathalyzer test, which measures BAC in the breath. They may confirm their BAC reading later with blood or urine testing. Someone who has been accused of having a BAC over the legal limit might want to contact a lawyer to learn their options.