If it is gcar on gcar, it is googles fault, because they programmed it wrong / poorly.

If it is gcar on car, with the normal car responsible, it is the traditional fault model.

If it is car on gcar and it is gcars fault, Google really fudged it up.

If it is no ones fault (ie, falling rocks on top of the thing) then that falls into the same catagory as natural disaster damage.

I would hope, at least.