Both deck trusses are complete and waiting for the Bowser handrail stanchions to arrive before getting painted.
Meanwhile, I've started building the deck plate bridges. The first of the two is now complete and I've started on the second one. These get mounted at a modest angle to each other so the O-88 curve track catches all parts of the bridge structure for good support.
Rather than spend the time and aggravation of building the inner cross-bracing structure, I realized that I had enough Plastruct 1-1/8" big I-beam to use that as the spacer and as a major structural member inside the bridge. How and where this bridge will be installed, no one will ever see the insides, and the I-beams are very strong. I glued two, flange-to-flange, to make an inner piece that is almost exactly the right size to sit inside the girders. This was just dumb luck since the depth of the girders (2.4") was more based on aesthetics than anything else.
I worked hard to ensure that all these parts where the exact same length and square in both directions. I used a v-block clamped to the I-beam to support the part during gluing. All gluing is done with Plastruct Bondene plastic weld solvent.
I wasn't sure how to handle the bearing surface where the track actually contacts the bridge structure. I first tried to use 5, H-beams laid cross-wise across the girders, but didn't like how it was supporting the track, so I went to Plan B which was to make a level bearing surface across the bridge to ensure that the track touched everywhere. The structure is extremely rigid and has no flexing in any direction. It's a solid plastic brick that will easily support any locomotive I own.
In the above picture, you can see the filler pieces that support the rails even when the ties are not touching the outer edge of the girders. With a deck plate bridge under straight track, you don't have this complication.
Here's some track laid across the bridge and you can see it is contacting all surfaces and looks exactly like the original design.
I still have to design the angle connection between the two bridge halves. The bridge shoes will go under this mid section. I'm leaning towards a solid square plate of ABS plastic that will span both bridges, and then some inner structure that will fill in the gap. I've got some .080" material left over from the truss bridges that will work perfectly when combined into a .160 sandwich.