Triple track curved bridge: N scale

[Sumpter250]

I need to build two bridges on a curve that are triple track. Track is Peco code 55 flex. I plan on just spreading ballast over the plastic base of the spans, no cork roadbed.

1. With a through truss span, there is usually no closed deck to ballast. You see this done with a through girder bridge.
2. In most cases, there is much less "train noise" on bridges, than anywhere else.
3. Your side trusses,( or girders ) need to extend from "support to support", as it is the trusses/girders that carry the load.