Agreed, risk of injury does not factor into how long the trip would take given faster speeds. This article is an exercise in narrative nonsense.
I don't think the article intended to be taken entirely seriously.
It's narrative nonsense, but I would argue that it's entertaining narrative nonsense.
I think it also serves a larger point, not about "optimizing trip speeds" but about putting into easily-digestible context exactly how dangerous driving a car can be.