The bridge in Columbus, MT collapsed under a Montana Rail Link train. MRL is class Ii railroad with 900 miles of track.
No info on cause but possibly a maintenance issue. Strange that the bridge failed mid-train rather than under the much heavier locomotive. Could be another derailment that damaged the bridge. Bridge design is ancient. Certainly not recent.
Haven’t read much but the initial reports, but it was said to be a derailment. Depending on where, the locomotive could have gone merrily across the bridge, and 10 cars back an axle broke, the (fully loaded) tank car headed east on a northbound train, taken out a supporting strut, and there you go.