I wuv RR bridges. Cool
Is that line closed? You could have probably got away with a close up of the bridge.
Walking on the ties is safer than the catwalk on many of those. If so you could really go app shit and get some one of kind shots. Dawn on a Sunday is a good time when people are scarce...
That said don't get by the RR police on active lines... they'll probably write if caught on a bridge.
Workers/engineers may dime you out if they see you.