I would have expected the concrete overpass to have received some sort of theming as well, but for almost 50 years the WDW Railroad has just passed under a generic concrete bridge. I'm setting expectations low...I can't imagine that's just going to be a dark, unthemed tunnel. I would expect something of visual interest in there, even if it's basic.
Line the walls with fiber optics and pump in the Daft Punk TRON: LEGACY score.