Ok I am starting a project that has been on the back burner and was moved up do to a purchase of a used 4314 Cargo Zone . I am working on using the metal trusses and plastic track for now .

The trusses fit right to the track and that would do but just does not seem very realistic ( if i ever wanted that kid or hobo to be walking the bridge and "oh @%^& here comes the train !" ) .
I thought about using a system X wall double wide as the foundation so the truss would attach to the lower side and the track could lay on top then on the side i could use the system X railing .
if the bride needed to span a large river or gorge you could use a system x pillar in the middle .
Basically before i tear apart castles or put in a lengthy DS order I would like input or ideas you may have done to make this project.