Its rare that I try to visit a bridge and hope to find it in a deteriorated condition, but I had hoped for that with this bridge so I could see the cast iron pipes where the concrete had fallen away. Alas, as frequently happens, I was too late. A visit to DC last weekend found this bridge undergoing what (I hope) rehabilitation. In either case, the arch barrel was covered in formwork. The cast iron pipes are probably concealed for another century now.
This bridge is much more than is currently described here. Sealed within this bridge is one of only two cast iron deck arch bridges in the United States (the other of course is Dunlaps Creek Bridge in Brownsville, PA). The Pennsylvania Avenue Bridge is unique, as the cast iron tubular arches of this bridge were designed to carry water within themselves. In other words, the arch ribs of the bridge are water mains. According to HAER they still carry water, encased within the 1915 arch bridge. They are visible both in HAER documentation and in Google Street View.