Atlas track system, at one time had curves for 9" diameter increments. O27, O36, O45, O54, O63, O72, O81, O90, My layout, small, was O45 inner, O54 outer with mostly O54 switches. At one time Atlas provided a free design software, long gone.
Atlas, Gargrave, Ross, you can create custom pieces as need. IMO. Mike CT.