Paved

Oh yes, the auto unloading facility and IMS terminal will be paved.

I prefer roadbed especially

I prefer roadbed especially homosote, only for branch lines and mainlines, and sidings. For a large yard, I'm sure you could get away with track on the plywood. The sound doesn't bother me at all.

I had a section on a previous layout that had ME track nailed and glued to plywood and lasted 30 years without any problems. When I was salavaging parts and some structures before I threw it out, tI was surprised how the track including thte rail was very durable and hard to trash.

Main Line

I would put cork under the main. On a short test section, HO scale, I have up it is 18in by 8ft I put HO cork under the main, N scale cork under the passing siding, and the spurs and interchange track are flat on the plywood. It looks a lot better then my previous layouts which were all one level. You can put small pieces of styrene or strip wood at transition spots to help gain the fraction of an inch where the different levels branch off.

Jack

Cheap and easy

You might consider water resistant gypsum board. It can't get any flatter than that. It should take spikes and paint well. It would also be easy to dig some slight drainage into the edges of the ties in places or add dry wall mud for grade crossings or simulate concrete. 

Even Vegas is not flat

Your vision, your choice. Plain plywood is definitely easiest.

I like scenery and notice things like ground irregularities, including paved areas in an urban setting. My little railroad has one urban area on flat foam without roadbed.  There I create slight rises and dips with Sculptamold finger-painted onto the flat.

Elsewhere I put down 1 inch of extruded foam over the plywood so it could be carved a bit.  A 4x8 ft sheet of 1" rigid foam in 2017 costs about $20, or 0.63 per square ft.

Other than the urban area, the mainline is on standard 5/16" cork roadbed and the sidings are down on the flat.  The transition is made with wooden door shims, 1/4" x 12" shim is a 2 percent grade.

I struggled with how to best

I struggled with how to best deal with transition from the height of track on roadbed down to the "flat" yard areas... My solution was to glue down the cork all the way to the edge of where I wanted yard tracks to be flat on the ground. I then used the palm sander with 80 or 120 grit, and slowly worked in a taper from road bed height down to flat foam. It is about 18"-20" from flat ground to "full" roadbed height.

Make sure whatever glue or silicone is well dried, and make sure to get good coverage so you don't have pieces breaking off as you are sanding. Go slow and not too much pressure on the sander.

Tom

I've used an electric palm

I've used an electric palm sander like Tom suggests when cutting down full-sized cork roadbed.  It worked well.  For the end of transitions, I use a foam rubber sanding block.  That gives me more control in "delicate" areas.

I find the trouble with foam

I find the trouble with foam is you can't spike it, there goes hand laid track. Haven't not used cork I wouldn't think you could spike it either over foam and have the spikes hold.  I have used homasote in the past with good results but was intrigued with 2" foam everyone was using don't really like it, it has good(easy to scenic)  and bad qualities (dents easy won't hold spikes, melts with Rustoleum paints, etc.)  If I ever do another layout it will be on plywood with possible homasote roadbed.  Zeke

Atlas track nails hold with

Atlas track nails hold with no problems when pushed through thin cork into foam IME using flex.  Handlaid  I couldn't say.

Road bed or not?

The yard is on plywood painted and some ballast and the main is on cork with better ballast... transition to yard (not shown) is on shim stock for window and door installs and is covered in ballast  

same questions

I've got some of the same questions about roadbed or not. More specifically I have a question about these transitions from cork roadbed down to plain plywood

Don't a lot of these 'transitions' take place at sidings that are accessed by turnouts? And doesn't that place the turnouts in less than optimum support??

(surprised that the OP never reentered the discussion?)

Keep the turnouts flat

You need to keep the entire turnout flat (not necessarily level, but no vertical curves) throughout it’s length and for a little bit past the ends of the turnout.  So if you have a turnout to a siding that’s not going to be on cork or whatever roadbed, you lay the roadbed for the turnout and far enough down the siding for the whole grade down to plywood. Then a few inches past the end of the turnout start the vertical transition curve to the grade down to the second vertical transition curve back to level on the plywood, sanding away anything that shouldn’t be there.  I used a belt sander for homabed in O scale, that’s probably a bit too drastic for cork in HO scale - the palm sander mentioned in previous posts sounds like a good idea.

@ Brian

If on a very few little inch your turnout or track is not really supported in the transition, when ballasted and glued this no more an issue, we don't run train which wheigt tons, glue and ballast are sufficient to keep the track on a optimum support in very short length  ( a small inch) no more.

Course we are speaking about no more than 1 or 1.5 mm Under the track no more.

If you are not sure about it, you can still place some piece of plastic or wood Under these not touching part of the track.

Keep it flat

As Ken said. don't start bending the rails down till a bit beyond the turnout frog. If the drop is not extra large you can usually get down to siding level a little beyond  where the siding becomes parallel to the main. I use various ways to create the ramp down but for short transitions you could just squirt extra caulking under the ties and let it harden up to create the ramp. ...DaveB

Thanks everyone

I've decided to lay the track on the plywood, it's worked out great so far. Sorry, I don't have any pictures!

Track Roadbed or Not

I had just about decided to not use and roadbed under the track,...just keep everything nice and LEVEL and attach ALL of the track to the plywood.

The question arose when I began to think of putting a number of my structures onto foam-core/board bases so they could be removed in sections to work on 'off-the-layout'. Of course I didn't want my track down below the level of that foam board. That's when I began to rethink roadbed for the track.

I'm in a bit of a quandary about this subject as it adds a LOT of complication considering the amount of track and turnouts I'm putting in.
 

One other consideration in my decision as to whether I will use roadbed is that I have quite a few steam locomotives, and these guys can have a somewhat rigid wheelbase with all those big drivers lined up in a row. They don't care too much for dips, etc

?????

Cork everywhere

If you want to plan ahead to putting bases under your structures, figure out what thickness those bases will be.  And then figure how high you want the top of the base to be relative to the top of the roadbed.  And then get roadbed that’s thick enough to put the track at the height you want relative to the structures.  A single layer of cork roadbed is thinner than most foam core board, so if you want the track higher or the same height you’ll probably need something thicker than cork.

Or you can cut out the plywood in areas where you want removable structures.  Or you could use a router to route out depressions for removable structures.

Or you could forget the foam bases and plop everything directly on plywood.  Which is of course simpler, quicker, and cheaper.  But not as elegant, and the end result might not look quite as nice.

Bright side pessimism: Most model railroads never make it to the scenery stage.  Maybe yours will be one of them, in which case why waste time worrying about it?  OK, just kidding here.  More of an observation on my personal history with layouts.

If ?

I think if I was going to consider some variation of this idea, I would lay down 3/16" foamcore over the whole deck, then razor cut out shapes (mostly rectangular) under those industries/areas that I might look to remove on occasion.

Then utilize thin cork (I think n-scale cork is 1/8" ?), or 1/8" floor linoleum for the mainlines.

I am a firm believer in NOT

I am a firm believer in NOT using any roadbed at all. I use not roadbed and have not used any for at least 40 years now. Instead, my layout surface is ceiling tile. I sketch onto the ceiling tiles where the track is to be, then carve a ditch on either side of the track. This represents the roadbed and cam be ballasted. It also provides drainage ditches and is a big aid in doing scenery. This method saves time and money, is cheap and works very well.

This 10 year old photo shows the effect after the ditches are carved. Track is glued in place with a dab of CA cement (superglue) here and there. I place a few dabs of CA then spray it with "kicker" that will harded the glue in two or three seconds.

For transition from country to town and yards the track is all at the same level. The ditches get shallower and fade away in town. Again, this works great for doing scenery.

Jim Six

That's neat James    

That's neat James