Why have all that geometry when you can use an alpha map. A 32 bit image has a layer that we can use to make the part of the image you don’t want transparent. Here I have found an image of a bridge. I use photo shop and create a new channel “Alpha Channel” I now select the areas I don’t want with the wand tool and begin tracing and filling with black in the areas I don’t want.

Bridge Alpha Map

Here I have applied the map to the simple mesh of the bridge. I will need to recontruct the bridge to have the same out line as the map.

Bridge Construction

After reworking the mesh the map now fits perfect and now to create the other bridge in the same fashion.

Bridge Under Development

Both Bridges created with alpha mapping

Railroad Bridge