Answer
Answers will vary here.
One side will argue that driving is dangerous as it is, and that there is no excuse to increase the danger factor by driving under the influence of alcohol.
They would recommend $0.0$ for the cutoff level. Maybe $0.02$, because one could inadvertently ingest alcohol through certain food items.
The other side will argue that people respond to alcohol differently. We allow people to drive with minor medication; we also allow older people to drive with poor vision or young people with little driving experience. In all of these cases, the risk of an accident increases on average, but we can not generalize this fact to entire sections of society (there are plenty older people who are good drivers). In other words, we expect a certain amount of freedom in society, including the freedom to have a minor amount of alcohol in the blood system.
Work Step by Step
Given above.
