I think it was after days of flooding and heavy rains. The crew was out checking a possible weak spot when it just decided to give way. Looks like there was a creek below that probably went through a culvert or pipe or something, but the excess water just cut out the whole thing.
Saw this one last spring. There was a lot of water standing next to the r-o-w. Probably caused saturation and softening. The fill literally became a slurry, which once the culvert went, simply sucked everything along with it.