When they are in the middle of the lane they are a traffic hazard - I don't blame the owners for them ending up there, S happens. But I bet the law would assign them liability if someone got into a traffic accident trying to avoid one. I could stop and get out and move them by hand, but when have you ever seen anyone do that? Everyone else just swerves around them. Better that someone "kicks" it back into their driveway than it cause a traffic accident.