One car fits on the rail for the turntable and can be turned in any of 6 directions.
Optionally I also provided short straight and curved pieces to allow easier connecting to other ends. The turntable-ring is a bit larger than a standard track piece which might cause some "tight" connections with standard tracks.
For an electric powered train the turntable might not seem to be such a good thing because you need to give it constant attention, but my son loved it nevertheless or just because of this.
OpenScad files are provided for your convenience. Perhaps you want to customize some details or use it as base for your own designs.
The hexagonal crossing
gave me some ideas. Because my son loved it so much I designed this for him.