With Policar track, any constant radius 90° turn can always be replaced with any other constant radius 90° turn: regardless of whether you're using R1, R2, R3, R4, or R5 pieces! To put it simply: all of the curve assembly pieces are interchangeable. So, if for example you grow tired of your layout, you can easily replace a 90° R1 turn with a 90° R3 without trouble.