I'd have to disagree with that. It's not that they're not impaired, it's that their degree of impairment is less. But is their ability to operate a motor vehicle impaired at 70? Yes. Their degree of impairment will depend on their driving experience and their drinking experience, but they will be more greatly impaired at high blood alcohol concentrations. There's no doubt in my mind that there's still a risk of accidents at that level. Scientifically, we don't talk about “Is everybody in the world impaired”, but rather, if you take any individual at that blood alcohol concentration, they will have a degree of impairment, even at 70. It will be less than that same individual's impairment at 80, at 100, at 160.
To answer your earlier question, my experience from working day to day with crown attorneys and police is that, at least in Ontario, there is only one jurisdiction that was regularly charging above 90. That was in the region where I live, in Durham, and they have suspended that for a time because of the large backlog of cases. They are now offering those individuals “careless driving”. So, practically, police officers charge at breath readings of 100 or greater, and they're prosecuted at those readings. Sometimes individuals show signs of impairment at the roadside, and when they're brought back, they may have blood alcohol readings that are below 100. They're charged with a paragraph 253(a) impaired. They may bring us in to support their impairment at those lower levels, but the main focus of that prosecution would likely be the impairment, due to the observations of the officers or other witnesses.