There are additional GIVENS in the GIVENS & DRUTHERS for consideration in designing a layout:
There are three types of horizontal space in a layout room:

1]   layout including right-of-way, scenery, buildings.
2]   people space – the “average” adult is an oval 21” wide [width with hands as side] by 14” deep [this is the dimension of greatest variability depending on weight and gender].  These are minimum dimensions as operators passing each other may want/need a greater space [hopefully it is just “cheek-to-cheek” vs “belly-to-belly” or “elephant style”]. 

3]   “administrative” space along the edge of the layout which includes waybill boxes, throttle cradles, electronic push buttons and “amazing” colored knobs, shelf for beverages, paperwork, etc.


For consideration in ongoing planning, below is an update of the Bottom Level with the people [colored ovals] and administrative space [3" wide "ruler"] added.  With this additional information, the aisle in the closet and between the north wall and the blob in the main room need to be well over 3 feet wide, at least 3 1/2 or 4 feet in some areas.  It also shows that the shelf for the main yard on the west wall can be up to 2 feet wide.  The green boxes are the areas where significant amount of track such as yards, industry groupings, interchanges which have more than one turnout, etc.  These areas can be against every wall except the long walls of the closet.  There will be no area where one switching area is above another switching area, hopefully.  It appears that with two operators at the main yard [west wall], three additional operators in the main room, and one in the closet, the layout can reasonably comfortably accommodate up to six operators running at the same time.

Also to aid in planning, a 1”=12” model has been made using foam core walls with mat board for the layout surface/shelves.  Straight pins are pushed through the foam core wall into the edge of mat board shelf.  Interchanging different width shelves and relocating the pins provides flexibly to visualize the changing layout design as changes are made to the shelf width and location/elevation and impact of the operator and administrative spaces.  In the model of the room there is one long wall and three wall pairs at 90 degrees to each other [one wall pair has just a 6 inch wall at the door].  In the photo below, two adjacent wall pairs have been moved to show the "blob" in the main room.  If you look closely, you might see the straight pins going in from the outside of the walls.

At this stage of planning, the yard against the west wall will be between the highest and lowest point in the around the room/closet helix.  There will be a single track above the yard [about the 60" level] and another single track below [about the 42" level].  This is to accommodate a 58" duck-under and a 42" swing/drop bridge at the door entrance while maintaining less than no grade greater than 3% grade.  For a 2.5% grade, it takes 40 inches of run to change elevation of one inch, not counting the transition in and out of level.