This basic layout uses 22" radius curves. It is a blend or circular and linear motion.
Using 18" curves, we have added a second line inside the first.
#4 switches connect the two lines, allowing access and egress from either direction.
We have used #6 switches to make a passing siding inside the upper straightaway of the inner loop. Sidings have been added inside the layout using #4 switches.Because of the possibility of reversing direction, the upper siding and switch in the right loop will have to be insulated and wired for reversing. If you do not wish to have reversing wiring, omit switches connecting the upper siding with the lower ones extending from the inner loop's lower right center.