Hi
I solved it using the arch and cables as you described without any broken links in hard mode. I think the trick is to create a slight ramp at the far end so the train will clear (Kinda Dukes of Hazzard). The train only goes one direction. Also the arch is a single Heavy Steel spine and Y's at the ends. I don't know how to post a picture here so If you want it (picture or bridge) I will email it to you.
Thanks
Twilightzone