Syd Schofield
Editors note: Welcome to the third article of a series on narrow gauge by Syd Schofield. The previous article is available by clicking here, or by filtering with the category “Narrow Gauge”. Syd welcomes discussions and feedback, which can be made by clicking on the comment link at the bottom of the post.
Of the many narrow gauge railroads that were in the US and Canada, a key factor was the roadbed requirement. The sizes of two feet, 30 inch, 36 inch and 42 inch for common carriers were established out of need and equipment availability. Private lines were influenced by most of the same conditions, all based on economics. While the standard and larger gauges were capable of heavier loads, the disadvantages were greater construction and equipment costs and less flexibility in traversing rough terrain.
Preparation of the route was less demanding such as smaller tunnel dimensions, roadbed width on ground and built-up structures, tighter curves and rolling stock accommodations. This lends itself to the small area we have available for our modeling. Slower speeds, shorter cars and trains and tighter curves gives us longer operating sessions and a larger sense of scale for a given amount of space. With the grand sweeping radius curves needed for a large articulated locomotive and many very long cars of the Golden Age standard gauge lines, most of us don’t have the space available for a suitable representation. Technically, a common surveying technique is to project a curve from the connecting straight (tangent) sections in degrees of turn per 100 feet which can be translated to a radius in our particular scale. Prototype railroad specifications can then be used as modeler guides.
As in civil engineering projects built on solid ground (as opposed to semi-liquid high water content soil and small, rounded stones) the structural base was prepared by excavation (cut) to the desired dimensions. Once the material is removed the remaining base is ready for roadbed. That same removed material, if cleverly planned, can be used for fill in the nearby shallow dips. Otherwise expensive “borrow” material and bridging structures must be used. The fill, like the roadbed, must consist of an aggregate of solid angular geometric shapes of differing sizes to minimize shifting under load. Supplements such as cribbing and retaining walls can be used. Care must also be taken for drainage and compacting, hopefully before use of the rolling stock. As these same rules apply to larger railroads, the smaller size and tighter curves of the narrow gauge railroad yields less effort and expense in the roadway preparation.