I'm designing a city building game in a huge 3D (without any notion of "top" or "bottom") space station (or rather, a space city). There are various functional buildings (vertices) connected by corridors (edges) forming a network (not a planar graph in general because 3D).

Each corridor is a bundle of multiple "ducts", which can transfer various resources (e.g. electricity, fluids, rails) between buildings. High speed transportation of passengers and goods is achieved by taking shuttle vehicles moving along the rails. To travel from point A to point B, a vehicle has to find a path e.g. A -> C -> B (where there are corridors with a rail from A to C and from C to B, but not from A to B directly), enter the A-C rail, transfer to the C-B rail at C, and finally stop at B.

The above are the basic rules for the game mechanics to work (i.e. a 3D network version of Factorio). What I would like to ask about is a plausible explanation for the vehicle mechanics.

I plan to explain the shuttle vehicles as working through similar principles of maglev. The typical vehicle is cylindrical in shape, with a hollow cylinder in the middle to embed a magnetic monorail.

Cross section schematic of an operating vehicle: enter image description here

The above mechanism allows a vehicle to rapidly move between two buildings, but since there cannot be end-to-end connections between every pair of inputs and outputs rails in a single building, a vehicle travelling A -> C -> B would need to decelerate when approaching C, then slowly route to the C-B rail and accelerate again. This greatly reduces transportation speed at junction buildings. To minimize the disruption of reentering rails on highways, I introduce a special "junction" functional building highly optimized as redirection nodes on a highway route.

A junction is a spherical building with an arbitrary number of corridors. Fluid ducts between corridors are connected through inner layers on the spherical wall. Meanwhile, all rails pass into the large hollow cavity in the junction center

When a vehicle enters the junction cavity, the rail does not exert any braking force on it. Instead, a strong magnetic field is formed along a diameter of the cavity that redirects the orientation and velocity of a vehicle so that it perfectly tilts to enter the next rail, preserving $\max(\cos\theta,0)$ of its original speed. In the case of highway routes with a single dominant input and output corridor, multiple vehicles can move through the junction at the same time by applying the magnetic field in the same direction.

enter image description here

Does this mechanism sound practical? It feels very dangerous and unreliable to apply a magnetic force to precisely "aim" a very fast vehicle into a small guideway rail. In particular, can we reasonably apply the right amount of magnetic force to multiple vehicles with varying mass/CoG/moment even though they are moving from and to the same pair of rails?

  • $\begingroup$ There's a worldbuilding question here, but we need to make some adjustments. (a) I recommend deleting the last paragraph. Per the tour we are not a discussion forum. Per the help center brainstorming is discouraged. Frankly, we focus on rationalizing imaginary worlds, so claims like "the amount of acceleraation required for this clam would be crazy and ... damage the vehicle" are simply rules of your world and only an issue if you want it to be. (b) The second-to-last paragraph could use some more focus. (*Continued*) $\endgroup$
    – JBH
    Commented Nov 12, 2023 at 4:03
  • $\begingroup$ ... Please remember that Stack Exchange's basic model is one-specific-question/one-best-answer and we've not nailed down how we want to deal with "review my idea" questions. Do you have a specific context you want us to consider? Engineering? Safety? Use model? Since particle accelerators basically work as you describe, there's nothing wrong with the idea. What, specifically, is worrying you about your design? $\endgroup$
    – JBH
    Commented Nov 12, 2023 at 4:05
  • 1
    $\begingroup$ ok I've deleted the last paragraph. It is more a reality check question indeed. $\endgroup$
    – SOFe
    Commented Nov 12, 2023 at 4:14
  • 1
    $\begingroup$ I searched on 'Maglev Train Switch'. The very first hit was a video of the Shanghai maglev railway showing one in action. It would probably need modifying to work in low g without throwing people about, but in either position, it 'looks' like a regular bit of curved track. $\endgroup$ Commented Nov 12, 2023 at 10:03
  • $\begingroup$ Your monorail design seems awkward... hard to remove stuff mid-rail if there was an incident. With a pair of external rails loading and unloading would be simpler, and switching no longer needs hail-mary throwers. FWIW, with inert cargo that can be readily accelerated, renegerative breaking and re-acceleration is likely to be very efficient and would significantly increase the safety of your proposal. Might make transport of live or delicate things slower, but you should be treating those things carefully anyway... $\endgroup$ Commented Nov 12, 2023 at 12:01

1 Answer 1


I think the center rail has several problems:

  1. It can't have a magnetic field that is repulsive all around. (at least not without a magnetic monopole, which doesn't exist in current theory.)
  2. It doesn't have any way to be supported in the tube.

Splitting the rail in two, and moving it to the outside edge (either top/bottom or left/right.) would solve both issues, and allow easier track switching. It could even allow the kind of "faith jump" you imagine for the junctions, if the walls still have magnetic guides with no actual rail.

  • $\begingroup$ For 1, is it possible to have the other pole in the vehicle itself? Or just a wall surrounding it? $\endgroup$
    – SOFe
    Commented Nov 18, 2023 at 4:03
  • $\begingroup$ @SOFe Nope, having the vehicle be one pole and the wall another pole makes them both magnetic monopoles. You can say your world has magnetic monopoles if you want, but afaik they're not believed to be possible irl $\endgroup$
    – M S
    Commented Nov 21, 2023 at 21:57

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