In 4.1.0 Right of Way I discussed how a railroad company got the land that it operates on. In 4.1.1 Roadway Roadway is planned and constructed based on the roadway engineering plan. The plan identifies all the issues involving construction, to include:
1) Geography: that is the roadbed, embankment, cuts and fills, drainage, and
2) Track structure: Ballast, Ties, Rails, Turnouts, Track crossings (Special works), and other associated materials.
In this page we will discuss the geographic issues in roadbed engineering and construction, specifically roadbed.
Prototype Information
Roadbed is defined as the finished surface of the roadway upon which the ballast and track rests. The roadbed of a railroad line is largely of an unstable nature. Instead
of seeking for a solid substratum, as is done when laying the walls of a
building or when constructing a pier or abutment for a bridge,
railroads take the surface of the ground pretty much as it is and, construct a roadbed that in
excavation, go only so far as a predetermined grade line has been
established.
Roadbed consists of four layers :
Finding a common standard from a prototype railroad can give you specific information on the specification of the roadbed for the particular line you are interested in.
Modeling Information
The rail layer can be be modeled with a variety of product (wood ties, flexible track or PC board). See 4.1.4 Rail for prototype information, construction, product and sceenic techniques.
The railroad tie layer can be be modeled with a variety of product (wood ties, flexible track or PC board). See 4.1.3 Ties for prototype information, construction, product and sceenic techniques.
The ballast layer can be be modeled with a variety of product (extruded
styrofoam, cork roadbed, vinyl foam tape, homosote or drywall). See
4.1.2 Ballast for prototype information, construction, product and sceenic techniques.
Sub ballast layer. Model railroads are built on benchwork and track support structures. The railroad sub-ballast layer is the model railroad track support structure. The model railroad track support structure can be constructed with the Flat top, Panel, Cookie cutter, or Spline construction techniques.
The WWSL
The WWSL uses the panel type track support structure, specifically a extruded polystyrene panel for the ballast and sub-roadbed layers. My preference is to use 2 inch foam bonded to 1/4 inch luan or masonite. This combination provides these features:
- The lamination seems to ease drooping of the surface over time.
- The wood layer provides a superior method to both attach the sub roadbed to the underlying support benchwork, and it also makes attaching switch machines easier.
- Weight, if it is a consideration, is much reduced with this system.
- Creating ballast profiles and drains are easily hot wired to whatever standard is used.
There are some issues.
- Foam edges can be bruised or dented with misuse.
- Running track feeder wires can be a challenge. I eventually found a six inch long 3/64 bit that I use to drill feeder holes and have sometimes had to thread a hardened wire up from below the benchwork to attach the feeder wire to fish it down under the layout.
The WWSL Maintenance Of Way department has identified 16
roadway types based on roadbed, ballast, tie and rail usage. See See 4.2.11 Roadway Types for additional details and modeling techniques.
Reference
Walter Mason Camp, Notes on Track, Google Books Chapter V.
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