Raised on the Erie Lackawanna Mainline- Supt. of the Black River Transfer & Terminal R.R.
Areas where people have to work in close proximity to tracks are usually pretty close to level, mainly to avoid tripping hazards. This includes a wider area of ballast extending about 150 feet in each direction from a switch stand - so the lucky person that has to dismount to throw it doesn't have to contend with the slope at the edge of the ballast. (I don't know whether this is an AAR standard or something mandated by the Federales.)
Yard tracks are seldom laid on individual ballast beds, since all the cars on them have to be accessible to car inspectors. Main tracks ARE raised on ballast above the general level of the adjacent yard. I have heard the body tracks of a yard referred to as 'the bowl,' presumably because anything entering or leaving them had to negotiate a slight elevation change to main track level.
I carve my roadbed from insulating foam about 10mm thick. The yard surface is simply a flat sheet of the same material. (Yard, in this context, includes a major passenger station and an engine terminal.)
Chuck (modeling Central Japan in September, 1964)
In most cases, the 'grade,' in HO, is on the order of 1/8 to 1/4 inch - visible, but hardly an obstruction to anything bigger than a Dockside or a GE 25-tonner.
It can be handled by cookie-cutting plywood subroadbed or by using shim material - which could be cork or foam that has been tapered with a sure-form or wood rasp.
I just lay my yard tracks, service facility tracks, and any other maintenance area tracks right on a sub-surface (whether foam or wood) that is the same height or level as my sub-roadbed. I am using WS foam roadbed for my roadbed, which is the same height as cork. To get the gradual grade from the yard to the higher profile main line, I use a shim shingle or cedar shake cut to width, painted, and tacked down. Use them as required for each of your access points.
Elmer.
The above is my opinion, from an active and experienced Model Railroader in N scale and HO since 1961.
(Modeling Freelance, Eastern US, HO scale, in 1962, with NCE DCC for locomotive control and a stand alone LocoNet for block detection and signals.) http://waynes-trains.com/ at home, and N scale at the Club.
I used large cork sheets for my yard/TT area, which is the same thickness as the cork roadbed I used. I used Midwest.
I used cookie cutter, and the plywood has a natural transition into the main, It goes from sheet cork to beveled roadbed.
http://www.midwestproducts.com/catalog_sa1.asp?srch_grp_id=8&sa1_id=18&sa2_id=21
Excuse the mess, I have a lot of work to do in my yard. All of these areas use the large pieces of cork. I'm using a low price Atlas TT, with the TT sitting directly on the ply, I cut a large radius in the cork for the TT, then add track, ballast/dirt/cinders/ weeds etc. Again this area not complete, I need to add planks to the TT deck, and more ground cover and junk.
"The true sign of intelligence is not knowledge but imagination."-Albert Einstein
http://gearedsteam.blogspot.com/
Yard tracks should be lower in the middle of the yard, and rise up toward the ladder on both ends. This helps keeps the cars from rolling out. Kinda looks a bowl.
Most cars in the yard have the air brakes bled off, for easier switching, just go in and grab a track and start kicking. If the yard is graded properly, should just need a little pin, and the car should go into the desired track, and not roll back out at you.
Most turntable-roundhouse areas are pretty flat, easier to work outside on stuff. Make sure there are enough oil-grease-sand droppings to make it look like the place is used. Many roundhouses had a slope in the tracks, so an engine could be rolled outside to be fired up. Safer than making a fire inside the building. The tracks then had an up-slope before the turntable, to help prevent engines in the pit. Makes a big mess if something ends up in the pit. Then if the crane also falls in...
Mike WSOR engineer | HO scale since 1988 | Visit our club www.WCGandyDancers.com