Miniature Trains in Heroic Scale

Mag-trains are the fasted way to get anything around a planet, but not everyth plane needs (or can afford) a comprehensive mag-train network. In many cases, a conventional steel-on-steel adhesion railway is sufficient. That said, the Imperium of Man does everything big and overwrought, so expect any serious Imperial trains to be bigger and heavier than the trains we use in the modern day...

Determining the Width of "Imperial Gauge"

4 Meter Gauge Proposal

Back-justifying from existing Warhammer 40,000 canon and historical military developments, the standard Imperial loading gauge aught to be capable of transporting a Baneblade. The Baneblade's smallest profile is its width, at 8.4 meters. Most loading gauges can transport loads slightly over double the gauge witdth. A gauge of 4 meters is therefore 'sensible' as a canon baseline. For reference, Standard Gauge rails in real life are 1.435 meters wide. "Imperial Gauge" rails would be three times wider than real-life Standard Gauge rails, using this logic!

According to Reddit the best fit for Warhammer 40,000's "Heroic Scale" is 1:43 scale; though the models are nominally in "28mm scale" - or 1:48 scale - Games Workshop plays their scale fast and loose. A 4 meter wide track in 1:43 scale is 9.3 centimeters wide, and in 1:48 scale is 8.3 centimeters wide. The best-fit pre-existing scale model rails of that width are the NMRA "3/4 inch gauge" or the NEM "III gauge", both of which are 8.9 centimeters wide (3 1/2 inches). Collectively, these rails are sometimes known as "3 1/2 inch gauge". For additional context, those gauges are both intended to be in 1:16 scale.

If the widest heavy-haul flatbed cars have a loading gauge slightly over twice the width of the track gauge, those miniature flatbed cars would be 17.8 centimeters (7 inches) wide at minimum. For context, the Munitorum Armored Container model is only 12 centimeters (5 inches) long. A loading gauge this wide could safely stack these standardized shipping containers transversely - sideways, in comparsion to the way intermodal shipping containers are stacked on rail cars in reality - and with space to spare! Such a configuration would convey a massive sense of scale to a present-day viewer, since only container ships can load shipping containers in this way.

2 Meter Gauge Proposal

Certain model railroad gauges are more popular than others. Standardizing "Imperial Gauge" rails at 4 meters wide pushes the model rails and trains out of common hobby gauges. This makes actually acquiring the rails, locomotives, cars, and accessories prohibitive (and expensive!). Making the Imperium standardize on a 2-meter wide track would make acquiring in-scale track much easier. A 2 meter wide track in 1:43 scale is 4.65 centimeters wide, and in 1:48 scale is 4.15 centimeters wide. The best-fit pre-existing scale model rails of that width are NMRA "G gauge" at 4.5 centimeters (1.772 inches) wide or NEM "1 gauge" at 4.445 centimeters (1 3/4 inches) wide.

G scale is a very common scale for outdoor "garden" railways, with rails made out of a variety of metals available for sale today.

A 2 meter gauge yeilds a loading gauge of just over 4 meters wide; for miniature flatbed cars on G scale rails, that means beds 9 centimeters (3 1/2 inches) wide at minimum. This would render the train totally unfit to transport a Baneblade, however many common Imperial vehicles can still be transported. The width of a Leman Russ battle tank miniature is 3 1/8 inches wide, the width of the current Chimera tank miniature is 3 1/2 inches wide, and the width of a Rhino tank miniature is 3 inches wide; trains of this gauge could reliably transport vehicles based on the Leman Russ, Chimera, and Rhino chassis. From an canonical perspective, it could be the case that Baneblade tanks must only be transported via the (much larger width) mag-train network due to their size, while the most widely-produced Imperial war vehicles can all be transported using either the steel rail or the mag-rail networks.

For the purposes of modeling practicality, I would suggest that the Imperium of Man standardized "Imperial Gauge" as 2 meters wide.

1.435 Meter Gauge Proposal

The real-life Standard Gauge used by many rail networks across the world is 1.435 meters wide. A 1.435 meter wide track in 1:43 scale is 3.34 centimeters wide, and in 1:48 scale is 2.99 meters wide. The best-fit pre-existing scale model rails of that width are NMRA "O gauge" at 3.175 centimeters (1 1/4 inches) wide or NEM "0 gauge" at 3.2 centimeters (1.26 inches) wide.

The primary reasons for choosing this gauge would be (in my opinion) the ubiquity of model track at this scale, and theoretically keeping closer to the scale of the armored train featured in The Battle of Cold Steel Ridge in the 5th Edition Apocalypse rulebook (though that locomotive was wholly scratch-built and not strictly designed for O gauge track).

Determining the Average Size of an Imperial Train Wheel

Imperial freight needs to move fairly quickly; one example might be ore traveling across a mining world's continents from strip mines to refineries, and refined material traveling to that world's singular spaceport. The steel rail trains should thus be capable of achieving 200 Kmph fully loaded and without special preparations. Under more ideal conditions, most standard streamlined trains should be able to reach 360 Kmph (and perhaps up to 10 mps). To achieve these performance metrics, I looked into real life high speed rail. The early Shinkansen trainsets and the TGV trainsets use driving wheels just above 900 millimeters in diameter. Reflecting this, I chose a standard driving wheel diameter of 914.4 millimeters (36 inches, for maximum institutional inertia). Modern train cars have various wheel sizes, but many also use 920 millimeter (36 inches) wheels. Taken together, this means that modelers procure one size of model train wheel to use for both the locomotive and the cars.

Such a wheel at 1:43 scale would be 21.265 millimeters in diameter, and at 1:48 scale would be 19.05 millimeters in diameter. The best-fit pre-existing scale model wheels are 20mm diameter wheels, commonly used for 1:87 scale 16.5mm gauge rails (NEM "H0 scale" or NMRA "HO scale"), or the less-common "LGB scale" rail. One notable modeling challenge will be the construction of custom extra-wide wheel axles and bogies, as no model railroad was designed to operate on this fantastical gauge.

As a design aside: I personally feel that one of the best parts of locomotive design is the large driving wheels present on steam locomotives. However, electromotive locomotives did a way with huge driving wheels for several reasons. Huge wheels are mostly needed to permit low-RPM steam pistons to apply their power band efficiently at higher speeds (at the expense of low-speed torque). Large wheels also exacerbate problems with wheel slip. All that said, I'm sure that engines with huge driving wheels exist in the grim dark future. I just won't be using them on all of my locomotives.