My answer is a shot in the dark from the hip, so don't put too much stock in it. I've always been under the impression that on a roadway that is fenced, if a critter gets out and causes a wreck, it is the owner of the livestock who is liable. On an unfenced roadway, it is considered "open range" and the driver of the vehicle is responsible.
About fifteen years ago, I had cattle summered with a neighbor and these cattle were grazing a pasture that had a county-maintained single-laned asphalt road running through it. Some out-of-the-area workers were building a new bridge across the Niobrara, and their boss didn't work these fellers late enough at night. They had the habit of going to town every evening and drinking beer, and thus drove erratically when they went back to their camp by the bridge at night. On one of these forays, the driver lurched into and killed one of my good Angus heifer calves.
This happened in September, and at the time 500 pound calves were worth a dollar per pound. I told the guy that had the calf lived until mid October, she would have been worth $500, but that I would settle for $400. He howled and complained, but my response was either pay the $400 or I would get legal assistance and try to get more. He grudgingly consented and finally gave me the cash.
As far as advice to you, chuckie, I would suggest adding a fourth wire to your fence. Three wire fences just don't quite cut the mustard for keeping cattle out of a danger zone. Sorry to be the bearer of bad news.
