Underground Rail

Lore & Background

On the alien world the player has crash-landed, the first rail network is a modest loop: a few tracks, a train stop, and a single locomotive hauling iron plates to the steel furnace. But the moment a second production line is added, that loop must cross another, and the player discovers the brutal truth of surface-only rail—trains queue, wait, and idle while the other line crawls past. Underground Rail is the elegant answer the game offers: a buried conduit that lets one direction of traffic vanish beneath the ground while the other rolls on uninterrupted. The two variants encode a simple but critical design choice. Underground Rail North buries the north-south passage; Underground Rail South buries the east-west one. Placing the wrong variant means trains in the intended 'under' direction will simply refuse to enter, and the junction reverts to a stop-and-wait mess. Choosing correctly is a small act of spatial reasoning that, multiplied across hundreds of intersections, separates a well-oiled mega-base from a gridlocked spaghetti of red-lit trains. In the broader narrative of the game, Underground Rail sits at the threshold between 'I have a factory' and 'I have an infrastructure project.' It is not glamorous the way a rocket silo or a nuclear reactor is, but every large-scale base depends on it. The player who masters underground rail early never has to think about junctions again; the player who ignores it spends the rest of the game watching trains honk in a four-way deadlock.

In Their Own Story

The dust had barely settled on the new copper smelter when the first train hit the junction and stopped, its single headlight cutting a pale cone through the grey afternoon. The player crouched beside the track, watching the second train approach from the south, both now frozen in a mutual standoff. A long exhale. The inventory was opened, the Underground Rail South tile selected, and with a soft mechanical clunk it slotted into the intersection, its dark mouth swallowing the east-west line. The southern train shuddered, dropped a half-metre into the earth, and vanished. The northern train, freed from its wait, rolled forward with a low, satisfied hum. Above, the surface tracks caught the late sun and gleamed. Two lines, one tile, and the whole network breathed again.

Reader's Guide

Underground Rail is not a machine in the production sense—it has no input or output slots, no power draw, and no crafting speed. Its sole function is to let one axis of traffic pass beneath the other at a rail intersection, eliminating the mandatory stop that a plain four-way junction would impose. There are exactly two placeable variants. Underground Rail North routes the north-south trains underground while east-west trains stay on the surface. Underground Rail South does the reverse. You must choose the variant that matches which direction you want to be the 'under' traffic; placing the wrong one simply blocks trains from entering that tile. Placement rules: the tile must sit at the crossing of two rail segments. It cannot be placed in a straight run of track. Adjacent tiles on all four sides should be connected to regular rails (or other rail infrastructure) for trains to enter and exit. There is no stacking—only one underground rail per intersection tile. It pairs naturally with Train Stops (which you can now omit at simple crossings), signal logic (though underground rail itself does not require signals), and any rail network where two lines cross. In a well-designed base, underground rails replace the majority of four-way junctions, reducing queue times and removing the need for complex signal chains at every intersection.

Did You Know?

• Underground Rail has no power consumption and no crafting time once the Railway technology is researched—it is placed instantly like a regular rail tile.
• Trains do not slow down or stop when passing through an Underground Rail tile; they simply transition to the underground layer and back, maintaining their speed.
• The two variants (North and South) are functionally identical in every way except which axis of traffic is routed underground, making them mirror images of each other.
• A single Underground Rail tile can service an entire intersection, meaning a base with dozens of crossing lines needs only a handful of these tiles rather than dozens of full junctions with signals.