Curved truss bridge for HO trains

I have a starter Bachmann train set with a 36" circle track and I don't have room to make a bigger scene, so I need a curved bridge. I specifically called this “for HO trains” and not “HO scale” because it's not to scale of anything, but my 6-year-old doesn't know that. 

PLA, no supports (I was surprised!)

FreeCAD file included.