Zero Tolerance for Underage Drinking and Driving
Every state has a "zero tolerance" statute of some kind. These statutes make it illegal for a person under the age of 21 to operate a motor vehicle with any alcohol in his system. "Any alcohol" means something slightly different from state to state, but one thing is clear: this isn't about being "under the influence". While in some states zero tolerance provisions fall under the DUI statutes, it's not necessary to show impairment under these laws. Instead, the state must prove only that the driver had the designated concentration of alcohol in his blood.
In most states, the "designated concentration" is .02 percent. A 180 pound man can typically reach a blood alcohol concentration (BAC) of .02 after one beer. The intent is to prevent underage drivers from consuming any alcohol whatsoever before driving. In fact, that intent has led several states to set the cut-off at .00. That is, any underage driver with a BAC of greater than .00 is in violation of the law.
In some states, the penalties are administrative, with an automatic license suspension but no possibility of jail time or criminal conviction. In others, however, underage drivers who have been drinking are charged with DUI or a related crime. Under both civil and criminal statutes, penalties are typically more severe for subsequent offenses, and breathalyzer test refusals are often treated in the same manner as measured violations.
In addition, underage drivers subject to zero tolerance prosecutions are often charged with additional crimes such as consumption of alcohol by a minor or possession of alcohol by a minor.
The bottom line: drinking and driving is a high-risk proposition if you're under 21, even if your BAC is nowhere near the "legal limit" generally applied to drivers over the age of 21. Even an adult driver may be subject to DUI conviction if the prosecution can show that although his BAC was lower than .08 percent, he showed signs of impairment. For drivers under 21, though, the law doesn't prohibit impaired driving. It prohibits drinking and driving, period.