Hello Sboon, Thank you for your quick reply. Actually I have a computer science background (and almost nothing in railway design). I don't know if it is better to choose : 1/ An offset alignment + 2 assemblies (SingleRail) 2/ An offset assembly + 1 assembly with 2 sub assemblies In a curve, there is a cant value. I supposed that each rail should have their own cant value and should be interpreted separately. So, is the solution 1 more simple and more suitable for that ? Or the solution 2 ? Perhaps the solution 1 and 2 can have the same results ? Sorry if my questions are not cleared.