The staff-side route out of the Iron Tangle, part of the machinery that carried the team to their exit.
By the end of the fourth floor the Employee Line has served its purpose as the crawlers' back door through Iron Tangle, the piece of the network that let Carl and his team move where the crawl did not intend them to go.
With the floor closed and the team transferred first to the production trailer above the surface and then to the wheel room, the line passes out of use. It survives as one of the fourth floor's complicated features, exactly the kind of thing Odette says the audience complained about and that The Fifth Floor will not repeat.
Fourth-floor staff transit route, left behind as the team exits the Iron Tangle.