I think there should be more use of performance tests to determine, not just how "impaired" the driver is, but how well s/he is functioning at the time s/he is pulled over. And if you are impaired, it should not matter whether it's because of sleep deprivation, cold meds, alcohol, or what.

Not that drinking and driving is good, but a driver who is driving very slowly and carefully through town on the side streets in the wee hours of the AM (not holding up traffic) trying to compensate for having had a couple of beers is probably much less dangerous than someone driving 10 miles over the speed limit on the freeway, too confident because s/he is "sober."

Is there really any evidence that having a blood alcohol level of, say, .04 or .05 significantly contributes to car crashes?    Especially when compared to, say, going 5 to 10 miles over the speed limit -- which is pretty routine on the freeway.