If you are at a bar and a friend is staggering and stumbling drunk, most of us would try to stop that friend from driving. We all know that drinking and driving do not mix.
But if that friend seemed fine, even though we knew they had had a lot to drink, we might not think twice about them driving. When we hear later that they crashed and that alcohol played a role, it can be confusing.
We grow up in a culture that largely ignores mental impairment, which is a subtle form of impairment which, more often than not, is the causative factor in most crashes, even with alcohol.
Driving and marijuana do not mix: