Double and Triple Length Interchange Modules

Note: Though I originally called these "junction" modules, after some discussion with Terry Nathan I decided to call them "Interchange" modules instead. This should both help prevent confusing them with the standard "Steve Jackson Junction" modules (especially to layout designers!), and help clarify the design intent of them being an interchange to another division or railroad on the layout.

As I've designed them, these interchange modules have two main characteristics that distinguish them from the Steve Jackson Junction modules:

  1. They are designed to be multiples of the standard length module, so that they do not require an odd-length "makeup" module on the opposite side of the layout.
  2. Both main lines can run straight through the module without diverting if desired. This permits equipment that might not be able to negotiate the tighter clearances or turns of a "branch line" to bypass it (if necessary…) and still run on the main layout.

They do not provide the basis for a "bubble", as the existing junction modules do, but rather are meant to provide a free-form "out and back" to an end loop in the manner of BendTrack, or provide for a setup yard off the main layout that does not disrupt the standard layout geometry.

The idea came to me after a discussion about "easements" using Unitrack, and the concept of not being locked into the same radii curves through an entire turn seemed that it might be a way to approach the problem of otherwise "unclosable" track geometry.

To design these modules in XTrkCAD, I first connected two or three double crossovers together, since they are the exact track length of a single module alone. I then added a 62mm double track piece to each end, and removed the crossovers, giving me a "hole" of exactly the right length. I attached the necessary turnouts to the double track placeholders, then filled the rest of the double track main with appropriate lengths of track.

The next step was to start experimenting… what radius turns would bring me as close as possible to the 33mm track spacing when they converged? Would it even be possible?

I played around with different configurations and radii until I came up with the examples below, trying to make the "easements" as smooth as possible given the limitations of rigid pieces of track.

Each module is shown with the parts list required for it. They were all designed using XTrkCAD software. I have not as yet built any of these because I don't have all the parts necessary, so I would be very interested if anyone can verify the fit of the pieces.

The depth measurements for the modules are only approximate. I would strongly suggest laying them out and verifying the measurements before starting to cut any materials! They SHOULD work… according to the software.

Triple Length Interchange Module, #4 Turnouts (474mm x 928mm)

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This was the first successful plan I came up with, creating an analog to the standard junction on a triple-wide module.



Triple Length Interchange with #6 Turnouts (474mm x 928mm)

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After playing around a little more, it occurred to me that there might be room to use #6 turnouts on the interchange. There is! The curves used are a little different than for the one using the #4 turnouts, so this allows a better track configuration in the same space. Unless you have a good reason to use the #4 turnouts, this version is preferable!


Triple x Triple Diamond Interchange (928mm x 928mm)

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This one strains the interchange concept to the breaking point. Triple wide by triple wide, it can form a major junction for even the largest layout. I've seen double crossings before, but never one with the interchange options this has.

According to the software, it doesn't quite meet correctly on the curves, but it's a very tiny misalignment. Normally I'd say you could just finesse the difference and no one would notice… but there's very little room for finesse on this one.

I've broken out one of the quadrants in the picture so that it's more clear how things go together. Each quadrant is identical, and you could build them one and a time and snap them together at the end.

If someone has a lot of Unitrack and some time on their hands, give it a go and let us know how it works out. Be sure to stick a piece of double track on the end of each straight arm… and send pictures, even if it's just laid out on the living room floor!


Triple Length Interchange to Single Track, #6 Turnouts (483mm x 928mm)

If you want to run a single track branch line off of the main layout, this interchange will make it easy. This module creates a reverse loop, and will need to be gapped appropriately and (if you're running DCC) requires an autoreverser. The double crossover is optional, of course, and can be replaced with 186mm and 124mm straights on each line.

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Double Length Interchange, #4 Turnouts (316mm x 618mm)

This track layout compresses the triple wide interchange just enough to fit it into the length of a standard double width module. This interchange uses VERY tight turns, and some equipment may not be able to run on them. Trains with larger modern equipment can opt out of taking the corner, but it would be better to just use one of the triples above to enable everyone to use them.

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Double Length Interchange to Single Track, #4 Turnouts (390mm x 618mm)

This interchange has the same tight turn issues as the double track version, so is unsuitable for large modern equipment. If you want to establish a small branch line, though, or an interchange to a logging railroad, it might be just what you need.

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Example uses

While this shows a Double Length Interchange, either it or the Triple Length Interchange can be used in the same way.

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Here's how to use the interchanges to access an "off loop" yard for operations or setup. Note the single crossovers on modules adjacent to the interchange. This allows access to the yard from both tracks.

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Double Length Interchange compared to a standard "Steve Jackson" junction

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If you insist on (or have to…) use two Double Length Interchanges to create a "bubble", the opposite end of the bubble will be about 20mm short of closing if everything is perfectly aligned. If you have a long "bubble", then this won't really be an issue (there will be enough flex in the layout to permit joining the modules at the end) but it is less than ideal. Again, the tight corners are not "modern era friendly"…

Triple Length Interchange compared to standard "Steve Jackson" junction

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Again, the "Steve Jackson Junction" provides a more elegant solution to this problem, but if enough of them aren't available a pair of the Triple Length Interchanges can be pressed into duty as well. With a single module inserted between the corners at the far end, the gap between modules is 25mm. This can be closed by flexing the legs of the bubble, or by slightly spreading them and inserting a 29mm piece.

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