Legal limit

I've been watching the news. I shouldn't. It makes me angry or depressed...or confused. Tonight I am confused. They are talking about lowering the legal limit for drinking and driving from .08 to .05. As I said before, I'm confused. Is a person impaired at 0.8 or not? If not, why lower the limit? If yes, why was that set as the limit? Surely, we KNOW when a person is impaired, right? It seems to me this is something that would have been thoroughly studied. I know, that the number of drinks to reach impaired varies from person to person, depending on weight and tolerance...oh, and drink of choice. That is where people get in trouble, they think they can handle it. They think they are fine. They are not impaired. They may drive for years without a problem...until they don't. Yes, I know, in a perfect world nobody would ever drink and drive...zero blood alcohol. But we do not live in a perfect world, far from it. They say that lowering the blood alcohol level will save lives. How? People that have always driven drunk will continue to do so. Will the casual, glass of wine with dinner folks not imbibe for fear of crossing an invisible line into impairment? The biggest benefit I can see from lowering the level a whopping .03 is revenue from fines.