When RailClone is used to create pavements or curbs on closed corners, is frequent to get overlapping issues because the geometry intersects with itself.
Unfortunately when this happens, there is not an easy way to to fix it. But there are several techniques that can help to avoid the overlapping:
First at all, increase the spline's interpolation using Style->Curve Steps (i.e. with a value of 100).
If the path turns to both sides, we can mimimize the problem centring the segments on Y with relation to the spline. To do it, set for each segment "Y Alignment" to "Center (within the Style Editor)
Since the decisive value in this problem is the corner's radius, may be useful to adjust it dynamically. RailClone allows to create rounded corners automatically, setting the parameter Rules->Corner Fillet Radius in the Generator. In this way, we can check visually at what radius value starts the overlapping problem.
Sometimes may be necessary to refine the Segment's geometry, so it bends better on curved paths. To do it, select the Segment in the Style Editor and click "Extract Segment" (at the toolbar). A new object will be added to the scene, just select and refine it (i.e. applying a Tesselate modifier).
When the curve is so closed that any of these techniques works, the only way may be to use mitred corners. This can be done setting in the generator Rules->Corner->Bevel Mode to other value than "Disabled" (i.e. "Extend"). The Fillet Radius parameter must be zero.
In this image, you can see a sample using these techniques. Both using rounded or mitred corners.