This makes for a tedious process with lots of long slow cuts, so I tried doubling and quadrupling the material. Anything more than two and the blade would wander too far on the bottom piece and leave you with nothing but scrap.
Alas I got eight good two-foot long pieces that overlapped to form a three-foot long section. I used a standard wood block plane to smooth down the top (track) surface and screwed on a left over piece to the bottom side to make up for the variations in piece height. This is only necessary since this test section lives at the workbench. Normally, the pieces will (should!) get cut closer to desired size and the bottom just screws onto the risers or other benchwork supports.
So, it might be that future spline production is done from full sheets on a table saw outside. In mid-November, I'll be visiting a model railroad that uses this track support technique, so construction details will likely be some of my questions.
In other news...I ordered a full set of the tie rack jigs from Fast Tracks -- one of each spacing (20", 22", and 24"). My research trip did yield that the tie spacing was 20" -- at least on the remaining track where one could actually see the ties. This was close to a turnout, so I didn't take it as gospel that the whole line used this standard. Some variation, especially between more and less frequently used tracks will provide some visual appeal as well.
For this test track though, I doubt I'll wait until the jigs arrive. Shouldn't be too hard to lay 3 feet of ties by hand.
Looking ahead to track laying, I'll close with some prototype photos. It should be fun replicating track in this condition (and having it still operable)...