It’s a little known fact that every state has two separate drunk driving offenses: one for "driving under the influence of alcohol" (or, in some states, "driving while intoxicated"), and one for having a blood alcohol level above the legal limit (0.08%). The second type of offense—determined by blood alcohol content—is called a “per se” offense. Every state has recently added a per se offense to their basic law against of DUI or DWI.
But wait a second! Why does there need to be two different laws? Aren't they the same thing?
In a sense, they are the same thing: both offenses make it illegal to drive drunk. The difference is that one is more specific than the other. The second type of offense (determined by blood alcohol content) provides a more specific definition of what drunk driving is, and how to measure it.
Another way to think about it is that one offense is based on your blood alcohol, while the other is based on the effect that drinking had on your ability to drive.
There are a couple of reasons that have been given for having two different drunk driving offenses. One reasons involves something that most of us have experienced ourselves: alcohol tolerance. When it comes it alcohol, there are two types of people: those who drink large quantities and can somehow still appear relatively sober, and those who have one or two drinks and are—as they say—three sheets to the wind. Having two separate offenses allows people in both groups to be convicted of drunk driving.
Think about it: Someone with a high tolerance may appear to be sober, and even pass a field sobriety test, despite having a BAC far exceeding the legal limit. In principle, this person would be guilty of the second offense, but not necessarily the first. Someone else, on the opposite side of the spectrum, may be unable to drive safely, even with a BAC nowhere near the legal limit. This person would be guilty of the first offense, but not the second.
Another reason for having two separate crimes is that, at least in theory, being impaired and being legally intoxicated require two different kinds of proof. A person is impaired if coordination and cognition have been substantially affected by alcohol, regardless of blood alcohol content. Field sobriety tests, for example, are meant to determine a person’s level of impairment. On the other hand, a person is considered to have been legally intoxicated after the results of a chemical test (blood, breath or urine) show a BAC above 0.08%.
A final reason for creating two separate offenses is that anyone arrested for drunk driving can refuse to take any kind of BAC test (though not without serious consequences). Without test results, the state has no evidence to prove blood alcohol level. Having two separate crimes allows the states to convict a person of drunk driving in the absence of any BAC test results.
But here’s where it gets interesting, not to mention highly controversial. In most states, a person can be (and usually is) charged with both offenses.
How can that be? Isn’t that unfair?
Well, it gets worse, or at least more absurd-sounding. Remember that one of the justifications for having two separate laws is that each is based on a different kind of proof. In theory, that’s true. In practice? Quite the opposite. Failing a BAC test is considered sufficient proof for both offenses. In other words, the state doesn’t need any proof of actual impairment—of diminished coordination and cognition—to convict you of both offenses.
However, the good news is that, while you might be convicted of the two offenses, you will never be punished for both. In other words, double the charges does not mean double the sentence. Another piece of good news is that the second offense won’t have an impact on the sentence you receive for a later DUI/DWI. So, for the purposes of sentencing—both for your present case and any future drunk driving infraction—being charged with two offenses isn’t much different from being charged with one.