This is something observed in The Real World, not a model, but it certainly could be used in The Pretend World.
Made a pilgramage to Sacramento the other day, visited the California State Railroad Museum and Annex. What's the "Annex", you say? That's the adjoining boneyard, across the tracks from the museum, where they park the stuff they're working on. Fascinating bunch of equipment, including the hulk of a Krauss-Maffei diesel-hydraulic locomotive, 2 Santa Fe decapods, and a lot of MOW equipment, including a couple snowplows. They also occupy the old SP boiler shop and make repairs there.
Anyhow, the track between the Annex (my name) and the museum crosses the UP mainline just this side of the railroad bridge. I looked at for a minute, scratching my head trying to figure out how they got stuff across, as there's no rail crossing. Then I figured it out.
Some clever person came up with a temporary crossing arrangement. The rails across the mainline are slightly higher than the mainline tracks, so that the bottom of the crossing rails are at the same height as the top of the mainline rails. The crossing rails end several feet away from the edge of the mainline. There are two long rails sitting between the crossing rails, cut to the exact length between the two crossing sections. There are clips near the mainline rails. When they need to move stuff across, they pick up the rail sections, lay them ON TOP of the mainline rails in the clips, bolt them at both ends with fishplates, then make their moves. I'm guessing they also shove ties/wedges/whatever under the rails to help support them.
I imagine they move stuff r-e-a-l-l-y s-l-o-w-l-y with this arrangement.