Risers...track elevation? Access gate ideas?

You could buy 2x4x8's, cut to needed height/length and stand on ends, (on each side of the track, spaced 1-2 feet apart) then lay another section of 1/2" plywood over the top of the 2X4s. After that you could lay acoustic ceiling tiles over the plywood to deaden the noise if you wanted.

Kind of like pic below as an idea:

        here is a swing out gate at Clem's layout...

        https://youtu.be/OJcI8gByp6Y

                                       scenery on swing out gate...

I used MTH trestle supports and built this using Jim Policastro’s example in an earlier thread. Plywood base, soundboard next, and Fastrack. Sides are Masonite with balsa supports glued to the side. Coming back down I used graduated 2X4s with a soundboard base, as it was on the edge of the layout. The inner side is painted foamboard that I just went at with a screwdriver and knife. The outside is just Masonite facia. You can see some of the second level in the second picture.. I have bridges and tunnels I could show pictures of if it interests you.

Yes please...more photos would be great.  Any detail on procedure appreciated.

Thank you and everyone for your kind responses.

Speaking of pictures, Dr. would it be possible to show us what you have done and then keep us posted as to your process?

    here is one showing bench work, including risers ,

          and a another swing out gate...  https://youtu.be/MwABuBcnwzM

                     here is one with a lift bridge... https://youtu.be/mQO0zklvZYY

Hey John...love the trestle sides from Masonite.  How about a recipe for construction.  I am puzzled how you bent the material, especially the balsa to curves.

My layout is U shaped to get long runs and center access. About 7’ x 7’ of one end is covered by the upper level. The main loops under that section and the line going up to it loops on top and goes back to the trestles on a 2’ side elevated section with the three houses on it. I hav 3 storage sidings under each elevated section, plus real estate on top to develop. The lower line can enter or exit 3 tunnels before the “river”. I used concrete wall forms for support. They are 6” and should be 7”. Double stacks are very close running under. 

Hmm, in a world of $400 LionChief Plus locos, $18 per 4x8 2" foam sheet does not seem expensive.   In any case, you do not have to fill the entire space under an elevated section.   For instance, you could raise a 2" thick foam surface on 5" risers to reach 7" in height.   The risers could be wood, foam, or some other material.   I might use strips of the 2" thick foam on edge, for a 2" wide riser of any length up to 8', saving a lot of foam and conserving your $$.

You might consider accessing an internal area layout area using Lionel's 30" Lift-Out truss bridges as has been discussed in other threads.   

To use Woodland Scenics inclines with O gauge, I will sometimes use a pair of inclines side-by-side to get a greater width under Fastrack. 

I didn't take pictures when I did the elevated girder. I used 3/8" plywood for the base, then soundboard, and Fastrack. The sides are 1/8" Masonite 2" wide that I just used bar clamps to white glue them to the base. I used 3/16 square wood on the bottom, 1/8" square on the uprights, and a flat piece on the top. I pretty much used all my wife's clothespins and white glue to put them on. Everything followed the O60 and O72 curves with no problem with the clamps. I used a complete set of MTH trestles, shimming every other one to match grade. If you have a track plan, I'm sure you can get lots more advice by posting that.