Something to do with spare steel flat car bodies. I’d not heard of this before seeing this ad this morning. These look like they’re welded end to end, with beams underneath the joint.
Here’s a different approach, just the bodies on piers, side by side.
Last year when Craig @ctown2 was working on the rectifying issues with the OVR flat, he referenced a company that takes old 89’ cars and converts to bridges.
I’ve watched quite a few of the videos as they provide a wealth of modeling information on bridge and flatcar construction.
I have seen several flat car bridges through the years but never anything as fancy as these shown.
The ones I am familiar with were just old wood deck flat cars dropped on the ground across the creek and dirt pushed up at each end to make a crossing.
Thanks Dan, I guess I overlooked that reference.
Makes sense Rick. I’ve probably driven over a few without realizing it.
On a related topic, two of the V&T’s turntables became a bridge over the Carson River in the 40’s.
Thanks Dan for the polite reminder about that project. 
Well Craig,
You could change your benchwork a bit and add a 69’ wide stream/dry gully that needs to be crossed?
So in 1:29th that would be a 2.3793 feet between abutments and you could span it with the 89’ OVR flat allowing for 0.6897 of overhang before abutments and call it done. If anyone asks about the detail you could say it got washed out in the floods?
Just a thought?
I agree; but don’t you think four decimal places is a bit excessive?
But if you move the decimal it will change the size. 
Not when you strive for accuracy and this is why I model by the 10’ rule myself !
See quite a few former piggyback cars used for bridges when we travel through some of the rural areas of Ohio. Usually to bridge a ditch or small stream across a private driveway.
Regards, David Meashey