Liability occurs rarely? Try "never". At least there was not a single State DOT able to report any historic bridge related tort activity to an SRI Foundation study that I frequently quote.
Just another case of that ugly "L" word.....Liability. Although this rarely happens, the commissioners see it as an easy way to warrant getting rid of a historic bridge. Look at Switzerland County.......it took them 27 years to play that card! Signs posted at both ends saying that the user assumes responsibility would do the trick.
Here is a bridge that could have been left in its spot. The new bridge was built like 100 to 200 feet away. The county just took it down and only the abutments remain. It was not in the way of anything. This would have made a nice park area too.