I also don't think, if we were to do bridges, that it needs to be any more complicated than a single entry denoting a given bridge. For example, lines in a list file could be something like thus:
ColuRvr Cascades
OhioRvr US421
PotoRvr YellowLine
MORvr I-35
MSRvr CoonRapDam
MSRvr WashAve
In the above examples, which include Amtrak, other rail transit, bike/ped, and streets/highways, I used 4 letters to denote the river name and "Rvr" for river. In the case of the Missouri and Mississippi rivers, both of which have the same first four letters, I used their postal abbreviations. This arrangement could be adjusted to whatever the consensus wants.
I deliberately did not include state or region because for many major rivers, the river itself is a boundary.
For highway bridges that may have more than one span (like the Woodrow Wilson Bridge over the Potomac), it could either have a single point to denote the bridge or separate points for each direction to signify that each direction in such cases is on a different bridge structure. This can be left to the group to decide.