The problem with the limit, is allows for an alco to have his fix in the morning, then go to work,have a beer at lunch and then after work and still theoretically be under the limit -- that is alcohol in the system. They teeter on the limit, only takes one beer to send them over the edge, then over the limit.
Its scary a lot of people function like this.
Weed is another one, has zero tolerance where I am, regardless if you smoked days ago.. boom. busted. Do not pass go. Time to do the same with the booze imo.