Help on rail signals on this 73 TPM crossing

[fbsr]

Looking for feedback on the rail signals, mainly where 3 segments fuse into one. This is quite hard.
- Train size: 1 locomotive + 4 wagons
- Right sized signals

here's the blueprint:
https://factoriobin.com/post/mp5215

07-21-2026, 18-00-54.png (1.68 MiB) Viewed 522 times

[Fletch]

I generally follow the golden rule: "chain signals before intersections, regular signals after intersections".

Looking in your screenshot...

Top-left area: missing a regular signal on the exit of the bottom track (you have it on the top track correctly).
Top-right area: 2 of the 3 exit points are using chain signals instead of regular signals. 1 of 3 is already correct. -- but this is highly dependent on whether a train can fit in there without deadlocking the loop somehow.
Bottom-left area: essentially same problem as the top-right. 1 of the 3 has regular signal (good), 2 of the 3 have chain-signal instead (not so good) -- also highly dependent on whether a train can fit. Could potentially widen this to ensure a train can fit.
Bottom-right area: that one is correct already (chain signals in, regular signals out).

Nice design, BTW !

[Loewchen]

You can replace every single chain signal with a regular signal as there are no crossings in the whole thing. Some of the signals on the four forks on the far left and right could be removed as they follow very close but that does not hurt anything.
Placing additional signals on the off and on ramps of the circle will significantly reduce delay:

new signals

grafik.png (1.73 MiB) Viewed 419 times

[jdrexler75]

One thing that isn't about signals as such, but what I've learned to do for intersections that contain roundabouts like this: put each turnout ahead of the corresponding merging track: instead of both tracks being able to reach the turnout, only the one already on the roundabout can get there.

This way trains won't be able to path through the roundabout without going around the whole circle, which usually is much longer and more expensive than whatever minor obstacle they're trying to avoid through the roundabout. It keeps the roundabout clear for those trains that actually need to use it.

Screenshot_20260722_223613r.png (1.87 MiB) Viewed 393 times

You won't be able to place a signal in that section of crossing track, but it's not helpful there anyway.

[Jap2.0]

You can replace every single chain signal with a regular signal as there are no crossings in the whole thing.

Except entering and in the roundabout, right?

[Loewchen]

You can replace every single chain signal with a regular signal as there are no crossings in the whole thing.

Except entering and in the roundabout, right?

Yeah, if you really want to make sure that no train that cannot exit the circle may hinder a train that could. The problem with using chain signals in a circle is though, that they force a very big gap between trains because the chain is so long. I would expect that gap to be worse for throughput than the potential hindrance when an exit is blocked, especially since such a blockage is avoidable imo.

[mmmPI]

Maybe it's hard because there isn't a single way to do it, to me the picture in the OP is missing regular signal on the inner lane of the vertical exit ways, that's what makes me tick the most, the picture show train exiting the junction after a chain signal. But it would not change the functionning, just makes it more obvious where the junction ends and increase throughput by reducing distance between 2 trains.

As hinted , one risk with roundabout is to have trains deadlocking in them, when each block is occupied by a train, the use of chain signals or merger trick can avoid that but it can increase the distance between successive trains and hinder throughput. In that regard the initial blueprint appears "safe" to me.

But there are things that are looking like a rule applied with a bit too much rigidity, like those yellow blocks on the horizontal outer exit. There is the 3=>1 merger, where 3 chain signal guards a tiny block limited by a regular signal. Here typically, you can replace the 3 chain signals by regular signals, and remove the regular one after the merge.

[fbsr]

Thanks everyone for posting, i did testings with every suggestion and somehow, most decreased the throughput. Like those signals when 3 merge into one, when i replace with rail signals, it effectively reduce the throughput because now trains enter and stop inside the roundabout. That's why it's so hard, it's counterintuitive. The mod Testbenchcontrols helped a lot in testing the best configuration, that's how i got those numbers. After altering a few signals, it increased the throughput to 90 TPM:

07-23-2026, 20-37-54.png (1.05 MiB) Viewed 161 times

[Jap2.0]

You should be able to put the chain signal right as they enter the roundabout, and then have a regular signal prior to that—although I don't know how much benefit you get unless you expand that block enough that you can fit a full train in it (and even then, it'd be increased size in exchange for probably only a small throughput increase). You might also be able to make the circle more circular.

One other thing about chain signals is that they can cause trains to repath sometimes, iirc, which can be desirable in some situations (although obviously that's inapplicable when tracks are merging).

[mmmPI]

Thanks everyone for posting, i did testings with every suggestion and somehow, most decreased the throughput. Like those signals when 3 merge into one, when i replace with rail signals, it effectively reduce the throughput because now trains enter and stop inside the roundabout. That's why it's so hard, it's counterintuitive. The mod Testbenchcontrols helped a lot in testing the best configuration, that's how i got those numbers. After altering a few signals, it increased the throughput to 90 TPM: 07-23-2026, 20-37-54.png

The test bench automatically adds signals quite close to each other in the branches leading and exiting the junction, if you add similar "close" signals throughout your junction, you will increase throughput on the test bench, but also risk increasing problems if your trains are allowed to repath dynamically in a real game or try to loop around the junctions, this i think isn't tested in the bench, the advices are a little different for optimization or safety or minimum required.

what i described is just another convention for signals, since a merger doesn't strictly require "chain signal before and regular signal after" , unlike some other place where trains enters a loop, it can be used to reduce the amount of material in the junction, the throughput optimization is generally achieved with several "extra" signals compared to what would be the strict necessary as was pointed out.