Scenery
All main lines and sidings should have ballast. It is recommended that the track be fastened with the bonded ballast method. The ballast on the main lines should be a mix of fine and medium texture so as to blend together with adjacent modules. Ballast on all other tracks should be what is scenically appropriate.
# All tracks must be fastened down securely and only the connecting tracks may be removable.
# Area above main line tracks must be clear for a minimum of 25 scale feet (3.5 inches) to clear double stack and other excess height cars.
# Permanent scenery elements must not extend more than 12 or 24 inches above the bottom of the module so that the module can fit into the trailer racks without interference or damage. Scenery elements above this height must be made removable for transport in the club trailer.
There are no other limits on scenery except for height above track level. (Check Diorama and NMRA Clearance Specs.)