This thing is a derivative of both:Unfortunately, OpenSCAD had a problem opening Clothbot's file, so I had to run it through Netfabb to fix up the STL. It had even more of a problem with tc_fea's STL so I had to recreate it from measurements in his Sketchup file since I couldn't get a workable copy out of Netfabb.In any case, I cropped the train track, scaled it lengthwise to fit the bridge piece, and then trimmed it on the sides so it shouldn't interfere with the bridge supports.As best as I can tell, the horizontal bars in tc_fea's bridge pieces are to provide a little extra support since they're so thin (1.5mm). I figure that the much thicker pieces generated with the train tracks should give it enough strength to not require those supports. I've uploaded both STL's in case someone wants to put this to the test.After finishing the file I realized I totally left out the Thomas-train style connector pieces. D'oh!