I’m purely guessing, but maybe the traffic deaths have decreased linearly with traffic, and violent crime in some porportion to gathering size.

That is to say, that it’s due to less activity and not a changed mindset.

I doubt traffic accidents and traffic have a linear correlation. I would assume it looks very different depending on the density of the traffic, i.e. not linear at all.

Maybe it's not due social distancing, but the economic uncertainty.