A Swing Bridge instead of a Duck Under

[ngauger]

The height of the vertical 2 X 4 should be:

The height of the layout (minus) 1" for floor clearance (Minus) the thickness of the support "base board" (1 X 6 = 3/4 thickness

Got that???

So, you measure floor to height of benchwork... 36" and you are using a 1X6 (take away 3/4")
don't forget the "Bottom Clearance"..... ( take away another 1")

36 - 1 = 35............ 35 - 3/4 = 34 -1/4

34 - 1/4" is the length of that vertical 2 X 4. Why so long? You want it as long as possible for weight distribution. The 45 degree angle will be supporting the track and it must stay as level as possible, so it will align with the "other end" of the opening (Track).