Apparently Atlas HO scale flextrack (specifically their code 83 Super Flex-83) has revisions. I happened to have two pieces side by side and noticed minor differences between what appears to be revisions "A" and "C".

Based on feedback from LKandO, and my own dissatisfaction with the original design (especially the proximity of the yard throat to the mountain at the bottom-right), I've completely reworked the arrangement of the yard. Compare to plan in previous blog post. Key changes:

Here is the track plan of the HO-scale layout I'm starting to build. I'm calling it the Esquimalt & Marshall Hill. Prototype is purely freelanced, but based on the geographic concept of linking Vancouver Island to the British Columbia interior (and beyond).