One of my favorite milestones in any new Satisfactory save is the one which unlocks trains. I’ve quipped before that this game is a fun train simulator with a factory management system attached. This time, given certain of my goals for the save, I decided to really hunker down and use blueprints not only for the single flat and various flat and angled dual-carriageway pieces but also for the roundabouts. So far everything looks great!

Too bad about the junction bug, though.

What junction bug, you ask? I’m not entirely sure. A couple hours of Saturday afternoon was spent trying to get a handle on it, and I’m only calling it the “junction bug” based on my current deductions rather than any official word from the developers or consensus from the player base. Here’s what went down. (Sometimes literally.)

My goal was to connect a plastic-and-rubber production site at the west coast “Oilands” to the Caterium site at the edge of the abyss (which is to say, the waterfalls cascading into endless nothingness). Using various alternate recipes I intend to make 10 Computers per minute with enough Quickwire left over (probably about 280/min) to supply another production site of some sort elsewhere on the map later on. I built the first train station. I ran dual-carriageway blueprints down the coast, occasionally stopping down to place a roundabout blueprint set, until I made it to the Caterium site where I placed the 2nd train station. I dealt with a bit of trouble placing signals at that end of the line but before long, all the signals were green (except the ones that were supposed to be red) and I figured it was time for a test run.

And immediately the train pathing basically said, “No can do, boss. I can’t get there from here.”

Ooooooooookaaaaaaaay. I walked the route. Everything looked correct. I went back and decided to run the route “manually,” which is a bit tricky with roundabouts because of the need to choose switch positions at key moments to properly route your way through. This is why pathing automation exists, after all!

When I made it to the first roundabout along the line… I got the result you see at the top of this post. The train folded back on itself and tried to drive off the side of the roundabout, out one of the unused paths… an entry path at that. How the heck?

I figured there was something about the “auto-join” between the southern part of the blueprint and the dual-carriageway blueprint immediately after. So I removed and re-placed one of the rail segments and tried again. Success! The train made it through, and in fact was able to automatically path its way down to the Computers site station without further trouble.

Then I tried to get back north to the plastic-and-rubber supply station again. Second verse, same as the first. The companion rail piece to the first “problem child” also needed removing and replacement. Great! Problem solved, right?

Wrong.

Honestly, I’m not sure how the auto-pathing logic led to a train trying to launch its way off of an angled dual-carriageway segment I’d built off of the northern roundabout. If the train couldn’t “find” its way to the station it shouldn’t even have entered the roundabout. And yet, here we are, looking at a monorail engine having failed to achieve low planetary orbit.

I considered that it might have been the “Mk 1” roundabout blueprint to blame. The problem only manifested at the two of those in the chain, not at either of the “Mk 2” versions later on. (I made a design change partway along the route, mostly to reduce the amount of steel involved in construction as I was outpacing the steelworks’ ability to feed the dimensional depot. Also, the new ones look better.) So I ripped out the northernmost roundabout, moved it a bit, and placed a “Mk 2” roundabout. After connecting everything, I told the train to run the full route and observed the results.

The good news? It worked. The bad news? It… should not have worked the way that it did. I didn’t take video but I did take a screenshot and stuck some arrows on it. That’ll have to do.

To sum up: The train entered the roundabout, curved toward the right-side exit, performed a 180-degree rotation at that exit point, went across the roundabout via its straight pass-through segment, hit the entry point at the end of that segment, did another 180-degree rotation, and completed its trip through the round about “safely.”

Buh. Wut.

Here’s what I’m pretty sure is going on: At some point, either at 1.0 or the 1.1 update, Coffee Stain Studios introduced a bug wherein any junction creates a valid path… even if that junction is the “V” shape created at a split/join point. Somehow, not always but sometimes, the “180-degree mirror” option is flagged as a valid routing path, and sometimes is the only routing path, despite there being a connected rail continuing past that join point. I checked the official bug-reporting site and saw that I’m not the only one to have run into this, so now it’s a matter of waiting for the developers to get this fixed.

So why, you may ask, did the train just not take the full circular route around the roundabout? Because that’s not the shortest path in this situation (thanks to the bug). Remember: Automated train routing in Satisfactory will always take the shortest possible route. This is why you always build train stations “off to the side” of your main thoroughfares, otherwise you risk the station being “the shortest route” and creating bottlenecks. In the above diagram, using the two 180-degree-mirror points and that one straight segment is actually shorter than going the full curve.

Remember, this isn’t physics. This is video game logic.

For now, while I wait for a fix I’m simply removing unwanted and/or problem-causing segments from my roundabouts in an attempt to prevent the pathing system from including weird (or train-crash-inducing) options in its logic. I’ll have some hassles later, but in the meantime I should be able to enjoy stable rail-based good delivery service.

I hope.