On the scenario you have described here, my colleague was crunching some numbers without a calculator while I was listening to the question. He would say that the scenario you describe would result in a person having a BAC of somewhere between 10 and 45 milligrams of alcohol in 100 millilitres of blood at 10:30, which is the incident time, as we toxicologists refer to it.
Certainly this is not a very high level. If you are talking about 10, that is a very low level of alcohol. However, as I indicated during my presentation, if you take a person like this to the lab and test them on some very sensitive tests with skills that are relevant to driving, you actually may see differences in the performance at 15 as compared to zero. Does that translate into unsafe driving? I don't know. At 45 you'd certainly have more. There would be more skills impaired to a greater extent, and you're going to see them in more people.
Again, you have to differentiate between impairment and what you observe. You may look at somebody at the level of 50, 100, or even 200, and you might not see anything in terms of how they behave. It depends upon what they are doing. If they're just standing there and a police officer is talking to them, they might not show any signs of intoxication, particularly if they are tolerant, going back to your earlier question. If you put them in a car and put them into a very complex driving situation where there are a lot of things happening, where they have to integrate a variety of stimuli from the environment, like observing traffic signs, traffic signals, other cars, and pedestrians, and they have to process all this information, what alcohol does is it causes less information to come in and to be processed at a slower rate. In that aspect, a person would have decreased ability to operate a motor vehicle even at 15, certainly more at 45, and even more at the 100 or 200 level.