First, the rules: In the United States, anything north of 0.08 percent is against the law. This has become the generally agreed-upon measurement, even if it isn’t entirely agreed-upon. (More on that in a moment.)

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The Centers for Disease Control and Prevention says that when a driver is at 0.02 percent, they are less able to keep an eye on moving objects and multitask; once the driver hits 0.05 percent, they have trouble steering and coordinating. At 0.08 percent, though, drivers have problems with perception, concentration and speed control. Even higher percentages make it harder for drivers to stay in one lane (0.1 percent) and maintain control of the vehicle (0.15 percent), according to the CDC.

Nearly one-third of all traffic deaths in 2012 involved drivers with a blood-alcohol reading of at least 0.08 percent, reports the Department of Transportation’s National Highway Safety Administration. More than half of the drivers involved in these fatal crashes measured at 0.15 percent or greater. (More than 10,300 people were killed that year in these crashes. Just under two-thirds of the people killed were driving.)

The law of the land is that driving with a blood-alcohol level of at least 0.08 percent is a crime, though exactly how the crime is punished varies from state to state. (The Governors Highway Safety Association has a handy list here, outlining how the punishments vary in terms of length and what happens to the drivers.)

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Arizona added the “super extreme DUI” charge in 2007 to cover anyone with a blood-alcohol level of at least .20 percent, which can carry with it a sentence of 45 days in prison. The “extreme DUI” category in Arizona, covering measurements of at least 0.15 but less than 0.20 percent, has a punishment of 30 days in prison.

At what level is a person’s driving actually impaired? This has been the subject of some debate. The National Transportation Safety Board recommended last year that the U.S. set 0.05 percent as the limit for legal driving, citing research showing that the risk goes up once a driver reaches the 0.05 percent mark. Lowering the legal limit “would lead to meaningful reductions in crashes, injuries, and fatalities,” the leading federal safety advocate said in a report.

This isn’t a new theory, either. An article in the Journal of the American Medical Association published in 1986 spoke of the “scientific consensus that alcohol causes deterioration of driving skills beginning at 0.05” percent. The AMA recommended that all states adopt the 0.05 percent measurement for impaired driving.

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