I'm a Railroader with just a couple of years under my belt,I've always wondered about the origin of some of the slang that is used,any old heads out here? Tie-up,Tie down,mark up, mark off, these are just a few that come to mind.
I would hazard a guess that tie-up comes from when a horseman or
cowboy would tie up his horse at the end of the day at the ranch or saloon. vs tie up in RR speak is going off duty.