Slide out option to allow access to staging tracks and wiring, and to allow access to the underside of the main level yard for maintenance.

Slide out shelf may be 1/2" ply with 1/2" Homasote or some other, lighter materials, or possibly just straight 3/4" plywood.

Shelf as drawn would be about 14.5 feet (~ 4.5m) long. Clearances would be the same as described on photo 17; ~9 - 9.5 inches to bottom of the main yard above. Roadbed level is 33.5", track level about 3/16" higher.