AnyRail can create (near) perfect arcs, easements and straights from flex track.
To create a straight, curve or easement
Alternatively, click the flex, and select from the Ribbon:
Creating a precise curve (circular arc) is similar to straightening a piece of track.
An easement provides a smooth transition between a straight and a curve. Real railways always use them to avoid wear and tear, and to permit higher speeds. They also increase passenger comfort.