The number .08 is well known all over the US as the legal blood alcohol limit for drivers. Push the needle above that on your breath test, and you have a date with a judge.

But North Carolina has an extra provision you might not have heard about. If you have a DWI conviction on your record, your limit becomes .04%. That’s just two drinks for an average 160-pound male, and less than two for a 120-pound female.

At first this might seem pretty strict, but it’s important to know that at .04 BAC (blood alcohol concentration) you are certainly under the influence of alcohol, though not intoxicated. At .04 your inhibitions are lower, and you might have some feelings of euphoria – probably not the best attitude for driving. More important, your sense of caution is lowered and your concentration is impaired, neither of which makes driving any safer.

So why are previous DWI offenders the only ones to face the .04 limit? The answer is that it is a compromise, like all drunk driving laws. Imposing an .04 limit for everyone would mean that few people would be able to drink even that one glass of wine with dinner and be sure they were safe from arrest. That is not deemed practical in the US.

Some countries do have zero tolerance: Brazil, Hungary, and Saudi Arabia can arrest drivers with any alcohol in their system at all. A level of .02 is the limit in China and Sweden. But in the US the National Transportation Safety Board (NTSB) called for a reduction to .05 for the national limit, and got little support. Even MADD called the lower limit unrealistic.

However, persons who already have a DWI under their belt have shown a serious lack of judgment, enough so that the state of North Carolina deems the lower limit justified. At that limit, almost any drinking is discouraged. There is some leeway, but two good drinks will probably get you arrested unless you allow a lot of time for the effects to dissipate. And that, of course is the idea.

North Carolina’s DWI laws are on the complex side, and the best time to comprehend their ins and outs is not while you are facing a drunk driving charge. So stay away from alcohol while driving, and you can pay the numbers no heed.