I have worked as a Civil Engineer in the past (construction of nuclear power plants), prior to moving into Mechanical Engineering and Industrial Technology (degrees come with it too

). No real way to provide resolution through a picture but it certainly looks worthy of repair. And beside that, I look at things in a slightly different manner. The bridge has a certain attraction of character that a new concrete culvert could never duplicate. That said, the culvert would require an entire different excavation and infastructure for installation. Honestly, unless you're bent on doing a culvert, I'd repair that bridge and use it any day. The beams look like their size will accommodate most loads. They appear to be 10" - 14" beams, but again the picture may be misleading to my **** viewing.
All said, my thoughts are opinion based and biased because I like the bridge, just as I do old wooden barns, etc...
I really enjoyed the pics too. :tiphat: