I created a brick compatible train track rail system with more flexibility than full standard track pieces that can be directly attached to baseplates as part of city street scenes.  This model contains 4 build plates, the first of which has 90 degree curved rails with an inner radius of 21 studs, and an outer radius of 26 studs (this is a MUCH tighter turn than the standard 40 stud curve made by major brick suppliers).  The second plate contains straight rails that also directly attach to a baseplate.  The third plate contains 2x8 baseplates that can be used under track pieces to hold them together and raise them in line with larger baseplates they may be attached on.  The fourth build plate contains adapter pieces to transition from standard brick track pieces to the straight ends of the baseplate rail pieces.

The explainer image shows how the various pieces are connected together for a wide variety of possible track arrangements.

If there is further interest in this, additional curved rail pieces could be designed for larger radii.