Modeling roadbed and superelevation

I like to model the different heights of roadbed found on the prototype. Full-scale railroads build sidings and spurs lower than the mainline to prevent errant rolling stock from creeping out onto the main in front of an approaching train. This is how the mainline got the nickname “High Iron” back in the day. Sidings are often 10 to 12 inches lower than the main, whereas spurs can be several feet lower, depending on their location.

I use Midwest Products cork roadbed to model this practice. I prefer the Midwest over other brands because it is more pliable, has finer grain, and thus is easier to shape.  My mainlines use two layers of cork; a layer of HO cork on top of a layer of O gauge cork. The two layers are the same thickness, but the O gauge layer is wider; this gives a realistic “two-step” appearance to the mainline roadbed cross-section. I use white glue to secure the roadbed to the foam top layer of the layout.

Branchlines and sidings get one layer of HO scale roadbed. The most important part of this whole method lies in ramping down the top layer of the mainline into the single layer used on the siding. To do this, I lay the top layer of cork 14 inches past where the end of the turnout is located, into the siding. Once the glue has dried overnight, I use a Surform rasp (available at Lowe’s or Home Depot) to feather a downgrade into the siding. I work slowly and carefully, using a 12” steel ruler to ensure that I’m not introducing any vertical curves into the incline. The first four inches out of the turnout is dead level, while the remaining 10 inches ramps down to the base layer of cork. Given that the roadbed is 3/16” thick…Quick! Do the math!…falling 3/16” of an inch over 10 inches results in a nominal 2 percent grade, which is perfectly acceptable.  

The same general procedure is used for spurs, with the caveat that since N scale roadbed is used on spurs, the mainline roadbed has to ramp down slightly steeper since the N scale roadbed is only 1/8” thick.

“Hold on a minute” you say. “N scale roadbed isn’t wide enough to give a sloped cross-section past the ends of the ties in HO scale…”

It does when you backfill with ballast, shaping a new shoulder as you go. And the N scale roadbed is just the right thickness to imply a slight elevation above the surrounding ground.  

When I have finished shaping all the ramps, I like to paint the roadbed with light gray latex interior house paint. This accomplishes two things; (1) it seals the roadbed and makes it nearly indestructible to any moisture introduced during the ballasting process and (2) it helps disguise any areas with thin ballast coverage.   

In closing, a quick word about superelevation. I use a 30” minimum radius on mainlines and I like to superelevate. To do this, I superglue a strip of .030” x .030” styrene under the outside rail from easement to easement. I don’t bother fashioning transition ramps for the superelevation, I just let the track float for a short distance over the easement. It is fully supported once the track is ballasted.