NYC and later Penn Central Concrete Arch Model Railroad Bridge

This is a NYC, then Penn Central concrete arch railroad bridge, described at the following link:
https://historicbridges.org/bridges/browser/?bridgebrowser=michigan/oakwoodsmetroparkrr/

This bridge is located in a lowland hardwood forest, south of Detroit, and is a nice concrete arch bridge for crossing a river.  It is still in use by Conrail.  

I have included a 3mf file of the three unique parts that are required, one arch connected to each bank and one interior arch, with a 80 mm bridge width and a 15 degree skew, which is close to the prototype bridge dimensions.  If you need it skewed in the opposite direction you can use the PrusaSlicer mirror function.  A second set of parts are needed for the other side (obviously).  The bridge can be customized by downloading all three .scad files into the same folder and opening the PCRR Bridge V9.scad, and open the customizer window.  There are options for turning off the grid and the pillar incise if you don't want them. I got errors while generating the model, but PrusaSlicer was able to fix them and it sliced without a problem.  PrusaSlicer also ignored the extremely small vestigial defects in the model.

Once I have painted the model I will post a photo. I was able to visit the bridge and took the cover photo.  The water level was lower when I was there than when the photos were taken for historicbridges.org, so I was able to see more of the armoring to protect the piers from ice.  However, all the dimensions are estimated from photos and there is extensive spalling, particularly of the armoring, so the exact geometry is approximate.  

Note that the concrete used for the arches appears a different color and texture than the concrete used for the spandrel (the walls on the sides above the arches).  Even though the pillar faces are flat, the continuation of the arch through the pillar is easy to see in the photos due to this difference in concrete.  As with other concrete arch bridges the painting/weathering can do a lot to improve the appearance.

This bridge was an experiment to use solidPython2 to generate the geometry, and I included the python program if anyone is interested.  

Update May 29, 2023: Found a minor interference at the armored pier and changed the bridge width so that its the clear space inside of the parapet.  The other two files were not changed.

Update June 8, 2023: Raised the top of the parapets at the pillars to match prototype in PCRR Bridge V3.scad, other files were not changed.

Update November 8, 2025: Added option to have reliefs on the hidden faces to reduce the potential for warping while printing. Also corrected minor error in geometry so skew angle is correct.

Update November 16, 2025: Internet wisdom is that no 3D model should be trusted unless the poster shows a photo that they actually printed it. Well that photo will have to wait for me to get some paint, but I did make some minor improvements when I finally decided to print this bridge. Along with fixing some more small geometry issues, I added a single layer (0.2 mm) incise where the construction joint between the arch and the spandrel meet on the central pillars. There is only one square dowel in the model, but I needed 17 for my three arch version. The parapet is printed separately and there are holes for 1.75 mm filament to align them onto the top. I have ironing on the top layer, which worked great, along with 15% support cubic infill. The 3mf file can be opened in PrusaSlicer and you can see the rest of the settings. There is still sanding on the retaining wall and ice armor, and then painting, but the model assembled well.

I have learned from this that making 3d models is much easier than painting them realistically, but at least I can print it again and start over if it gets too bad. I have attached photos of the partially painted model and how I glued up the middle section. I glued the two end arches first, which seemed to work well.