Transition Strips are used when traversing  from Mainline roadbed to Branchline/Siding roadbed, or vice-versa.  Scale dimensions are 18" at one end and 12" at the other.  The width is 11'-6" across the top and 14'-9" across the bottom.  Actual dimensions are 3.9 mm across the top (approx. 1-19/32" ), 5.1 mm across the bottom (2") and 10-1/2" long.   There are 2 transition strips for each unit ordered.