It follows street-tramway practice: the moving tongue sits on the inside rail of the curve, the outside rail has a fixed mate, and the wheels cross the frog on their flange tips. Set the road, then run a bogie through.
A short blade in a housing, pivoting on a pin at its heel. Set straight, its right face lies exactly on the gauge line and becomes the running rail's gauge face. Set diverging, it swings across so its left face lies exactly on the curve's lip line and pushes the back of the flange into the curve. The curve is guarded from the tip onwards.
The outside rail has no moving parts: the two flangeways simply run into one another. It carries the flange but does no steering; the tongue on the other rail steers the whole axle. That is the traditional street-railway arrangement, with one moving part per turnout.
Fixed · no moving parts
Where the curve's outer rail crosses the straight's inner rail, the groove floor rises to just under the flange depth. The wheel rides across on its flange tip, lifted a tenth of a millimetre, so there is no dip or clatter and no guard rail to add.
The printed road drops by the ply thickness, leaving the rails, lips and tongue housing standing proud. Laser-cut plywood drops in, cut 0.1 mm clear of every printed edge, and scored as wood-block paving: courses of 9 × 3 in blocks across each road, staggered half a block, with a border course along every rail. Gaps too narrow for ply stay printed, flush with the ply top.
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These use the coupon defaults. Once your coupon results are in, the groove width, flange-bearing depth and curve widening will be set from what your wheels actually need, and the tongue throw follows from the groove width.