Would the JJS plate girder bridges work? He made some that are bendy splines and not bendy. They work pretty well in all versions of Trainz from TRS2004 right up. The only thing you'd need then are the supports and abutments, but I'm sure you could find something similar.
Of course, if Ben wants to make a custom bridge set for you, well that would be really wonderful.
Thank you Ben! Here are a few pictures of what's left of the old viaduct. As you can see I believe they are poured concrete and made around 1930. John had a good idea of using the JJS plate girder bridges. I took a look at them and I think they would do the trick if I could some how ether have a spline using the piers below or some different sizes. I don't think they would be any taller than 50 or 60 feet and support a 2 track bridge. Please don't goto any trouble. By the way I got your Western Hills Viaduct and it looks great!
Here is what's left of the viaduct.
Looking at the old track plans there was a southeast and southwest approach coming from the banks of the Ohio River with the southwest approach going under the Southern's Bridge before rising to meet the bridge and entrance to the southern end of the Cincinnati Union Terminal rail yard.