Just thinking about small triangles I think the solution for a single line triangle is as follows. I refer to the three tracks coming in as A, B and C.
Insulate both rails of sides AB and AC of the triangle just beyond the point where track A diverges to form these two sides.
If A is a stub end (or doesn't connect back to B or C except through the triangle) then just reverse the polarity of A and its point according to which way the point is set. No reverser necessary.
If A connects back to B or C by another route then insulate both rails of A one train length away from the other insulated breaks, and feed the intervening section through a reverser. This should work with trains standing on both AB and AC, but not for unsignalled type layouts where trains can queue up on track A and therefore possibly bridge the rail joints.
Insulate both rails of sides AB and AC of the triangle just beyond the point where track A diverges to form these two sides.
If A is a stub end (or doesn't connect back to B or C except through the triangle) then just reverse the polarity of A and its point according to which way the point is set. No reverser necessary.
If A connects back to B or C by another route then insulate both rails of A one train length away from the other insulated breaks, and feed the intervening section through a reverser. This should work with trains standing on both AB and AC, but not for unsignalled type layouts where trains can queue up on track A and therefore possibly bridge the rail joints.
