So, what did "traffic boner" use to mean?

"Boner" was short for bone-headed. Still, sort of the same meaning as we use it today. Unless you're talking about the idiot kid on Family Ties.

But, like the movie said,
"I do not think it means what you think it means". I can't fathom why they would use it in that context: someone else's mistake has no relation to stop n go traffic efficiency.

Ah, thanks!

Surely you've seen the Joker's boner in Batman #66?

You can find page scans on-line if you look. It is a comic that truly hasn't aged well.

Oooooh my. No, hadn't seen his boner-- err, I mean, that issue. Ahem. :)