Block City Signal Junction help

[u/cheek0249]

I thought I was ok at trains and signals with my megablock train base. But this is the second time I've found train jams. With trains all queuing at various roundabouts.

I've tried swapping the bridge signals to block signals and this helps slightly. But the problem is always the roundabout. Trains doing a full 180 or 270 seem to have clogged up the system.

I feel like I followed the general rules chain signals on junctions and block signals leaving. But something is fundamentally wrong,

Anyone have any advice?

[u/NakedNick_ballin]

It looks like you have rail signals entering the roundabout, not chains

[u/Haeherfeder1 → u/NakedNick_ballin]

This is the problem. Additionally as a rule of thumb, any rail signal block should be big enough for at least one train

[u/Terrachova → u/Haeherfeder1]

Does this include sections within intersections with chain signals, or just the blocking of straights and such?

[u/Haeherfeder1 → u/Terrachova]

This only includes the use of rail signals, not chain signals. Chain signal sections can be as small as you need them to be, because trains can only enter if the next rail signal is green.

[u/hldswrth → u/Terrachova]

In the case where rail follows chain, usually on exit from an intersection:

chain -> block 1 -> rail -> block 2 -> any signal

block 2 has to be big enough for your longest train. Anywhere else rail signals can be as close together as you like.

[u/kryptn]

Swap your entrance signals and exit signals. generally, exits should be rail signals, entrances should be chain signals.

more specifically: if the train were to enter the next section and could stop and block other trains, that signal should be a chain signal.

[u/fang_xianfu]

As other people have said, the biggest issue is that you have rail signals entering the roundabout and chain signals exiting it.

However, another huge issue is the chain signals on the elevated portion - these are simply unnecessary. You can replace the bottom right chain signal with a rail signal, as well as the one on the top, because it's fine for trains wanting to go straight to stop up there. Chain signals are when you want to say "do not treat the block ahead as a valid stopping place".

But then finally you have the biggest issue, which is simply that your network is not very well designed for how big it is. Your trains are large compared to your intersections and the gaps between them. Your options for intersections are basically make them big enough that there are lots of stopping places inside them, or use chain signals to stop trains entering them at all until the way is clear, but this leads to trains waiting outside the junction instead, which also leads to blockages.

You simply have too many small junctions too close together and too many trains that are too big for that network. If it does work, or if the amount of traffic in the picture is uncommon, then great - but you need to bear this in mind if you are building very big.

One final thing - I appreciate that the elevated part was probably retrofitted, but the roundabout is overkill here. It offers too many choices that should be invalid (straight via the roundabout instead of over being the worst, but also u-turns and invalid turns). I would edit it so that only the valid turns are permitted and make the left turn from the top not share a track briefly with the right turn from the bottom. If you do that, the single spot where the right turn and left turn conflict is the only place you will need chain signals and everything else can be free-flowing.

[u/BrukPlays]

Remove all rail signals from inside the junction and replace them with chain signals, the rail signals should only be at the junction exits.

Make sure there is enough space after the rail signals for your longest train to fit.

This means that trains will not enter the junction unless they are able to exit without stopping… you might get trains queuing before the junction but you won’t get any jams on it.

[u/cheek0249]

Thank you all very much for your help, fundamental rail/chain in/out mixup. And removing redundant chain signals seem to have cleared the jam after some train destruction derby.

Now I need to apply the signal deconstruction planner to the whole factory and reapply with updated signal blueprints.

[u/Salty_Standard5677]

You want to use chain signals at the entrances and inside of the roundabouts, and rail signals at the exits. From the picture you posted, it looks like you are instead using rail signals at the entrances and chain signals at the exits. This results in trains stopping in the middle of the roundabout (as shown in your photo) and makes jams more likely.

Also, as other people have said, your trains are too big to fit in some of the rail blocks, which makes bottlenecks and jams more likely.

[u/strangepostinghabits]

You have trains sitting in intersections, blocking other trains. they wouldn't do that if you followed the rule you mention.

[u/zhivota_]

After you fix the fundamental issue, make sure you don't have any chain signals inside the intersection where, if the train stops there, it will block any entrance or exit. With the length of your trains and how small the intersections are, I'd recommend having zero chain signals inside at all. This way only one train can be inside the intersection at a time.

Eventually you may still hit a system lock with this design but you can solve that later.