the Fillet Curve at Parameter will produce one new curve with just that very fillet at that very parameter
stupid example on rectangle: 4 corners → 4 discontinuity points → 4 curves each with its own fillet:
if I bake them and move around to check what’s the output:
we want to iterate filletting the very same curve again and again at different parameters, so need to take into account two things:
- we need a loop, in such a way we mod the curve and reuse it for the next iteration
- the curve was just filleted at previous iteration, so it changed: probably the list of Parameters for next iteration is no good anymore, because it referes to the original curve without fillets
there’s a magic component from @magicteddy that would make the world of difference to you in this case; it comes from a library of components he has written himself, not released as an official plugin yet, but that he published himself in this forum:
it’s called Fillet Multiple, and allows for those fillet at parameters to be created -I assume- simultaneously:
but if I use that on your final definition “as it is” it gives plenty of errors 
before I study your script a little bit, there’s just one thing I didn’t fully understand: you have sliders for Road width, sliders for turn radius, but what happens for instance when two different kind of road intersect each other, like a Majour road is intersecting a Secondary one? what turn radius should to be used in that case? always the greater of the two?