I was trying to find specs. for bridges and I stumbled across the CSX PDF. Page 17-27 were the most interesting, defently if you want your modelrail as close to the real thing as possiable.
http://www.csx.com/share/wwwcsx_mura/assets/File/Customers/Services_and_Partners/CSX_Industrial_Sidetrack_Manual_063003.pdf
http://www.csx.com/share/wwwcsx_mura/assets/File/Customers/Services_and_Partners/CSX_Industrial_Sidetrack_Manual_063003.pdf