The main argument for the use of culpability as a categorizer is that some accidents can be said to be independent of the behaviour of at least one of the drivers, for example, being shunted when having stopped for a red light (in a slow and controlled manner, at least).

I can’t stop now. I'm in rather a hurry.

“Fanny has been cutting roses, has she?” “Yes, and I am afraid they will be the last this year. Poor thing! She found it hot enough; but they were so full-blown that one could not wait.”

At least this year's overrun isn't as unmanageable as last year!