Nearly an SP...line?

Between the two peninsulas holding respectively South SF and Burlingame, the terrain along the room wall will cover a series of curved right of way that crossed in 3 levels.
As the Coast line is a double track main, I consider a simplified way to adopt the "true spline" concept. First simplification was to find a Ready-to-use strips of wood, and I found some "samba wood" strips of 1 x 0.5 cm with 2 meters length. Thats free me from the dirty job to cut (or have cut by the shop) the usual Homasote sheets. This will takes to have a sigle track spline done using "just" 5-6 strips. Good Start!
But ... I'm pondering about the land between two track .... and the double job to have parallel splines ... so I've take the short path: basically I use two strips each side of a double track right of way and ..... fill the land with multilayer plywood (1 cm high).
See here a drawing with a section of what I mean:

This way I still have the "auto-easement" capability of the spline method plus the property of give a natural contour to scenery approaching yards or flat land following the curve.
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In the meantime having a flat continuous support of tracks avoid to have steps or jumps on the junctions from spline to plywood parts.
( well, maybe all these are just reason i give me to justify what I've done? )
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(Left) A detail of the end of the spline intersecting the workbench :
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and (Right) 3 levels nearly finish!