The spacing will be determined by how you intend to work the yard and how you uncouple your cars. If you will uncouple your cars automatically with some sort of under track magnets, you can space the tracks a little closer together. If you will be uncoupling manually with your hands or one of the various designs of pick between the couplers, you will need space for your hand to steady the cars in between the tracks. Also you will need a little extra space between the tracks on any curved sections if you have curves in your yard.