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BH Photo #293712
Clearly shaped like a Pennsylvania truss. Does it function like a truss? I don't know. I don't think it's really an arch, but without stress/load measurements it can be tricky to figure out what it _acts_ like - but it _looks_ like a Pennsylvania truss.
It can't be plain concrete as those diagonals are under tension - and concrete is nearly useless under tension.
The construction date is from a comment on the Flicker page.
Looking at the upper chord, I believe this may actually be an extremely rare concrete pony truss, perhaps even a Pennsylvania, which would certainly be the only one I've ever seen! I think this because the upper chord is polygonal whereas rainbow arch chords are smoothly curved, and also, the web members clearly show the Pennsylvania truss configuration. I can't tell if it's fully concrete or concrete-encased steel, but very unique either way!
It is clearly a Rainbow Arch, but I doubt it is a Marsh Arch. Marsh Arch bridges don't seem to have diagonal members - at least not that I have encountered.
Found this awesome bridge! Not on NBI, and not previously listed on here. Now, is this a "Marsh Arch?" Or is it something else? I just listed it as generic "Concrete Pony Arch." Anyone with more info please comment.