This could save you cost : Freight yard, engine house, spurs, tertiary sidings, and even some bucolic branch or short lines, have track with little to no shouldered road bed..
So, if your RR has this type trackage anywhere, you can have it flat on the sub-roadbed (plywood right of way)..but, still with ballast glued in and around the ties..Then, if there is a main line thru the scene it's a nice prototypical effect having the main line up on shouldered roadbed along its entire line ..When the two types meet face to face in places, there are a few ways to make gradual ramps under the two different track heights as do the 1:1 scalers.. ..Actually you can put an entire yard on one big sheet of cork (as Alcomotive above states) because the tracks will still look like they're unshouldered.