Track bed or no track bed? - Model Railroader Magazine

I'm going to give you a slightly different take on the subject.

Why does the prototype have a raised roadbed?  Primarily for drainage, and also to smooth out the humps and hollows of running across the general direction of drainage.  Even in places as notoriously flat as West Texas the ground undulates.  So does the railroad, but less so - and there will be a culvert under the lowest point of each little fill.

In urban areas and in large yards the top of the ballast may appear level.  That's because there are French drains (perforated pipes) underneath it to provide drainage.  The manhole covers over key junction boxes are a giveaway.

So, how do we simulate this in a model?  Standard cork roadbed does a pretty good job of pretending to be the top two feet of HO ballasted roadbed, but it isn't the only answer.  Pink or blue foam can be carved with a knife or shaped with a hot wire forming tool (DON'T breathe the fumes!  Wear a respirator and work in a very well ventilated area.)  Plaster or drywall mud can be slip-formed.  Literally anything, from cedar shingles to pieces of drywall can be formed into the desired shape.  Note that less important track doesn't warrant (and doesn't get) the full mainline treatment.

One line I'm familiar with re-ballasted and aligned their main track several times, each time raising it a couple of inches.  A parallel passing siding didn't get that level of attention, and ended up a couple of feet lower than the main, sloping upward to mainline level at the ends so the turnouts would be level across all rails.

A Penn-Central yard I discovered in Illinois had suffered a drainage failure due to lack of maintenance.  It was literally sinking into the mud that should have been solid ground under the rails.  One track, gone past the point of usability, had been embargoed by nailing an X of scrap boards across the switch target.

In thinking about using roadbed, the emphasis should be on appearance.  Think about what you're trying to model, look at pictures of the real thing (or the real thing itself if you live nearby and model the present) and adjust your modeling to look like your prototype.  Any one size only fits the people who are modeling the exact same thing.

Chuck (Modeling Central Japan in September, 1964 - on carved foam roadbed over cookie-cut plywood)