Factorio Forums

Hello all,
I'm trying to make a roundabout able to have two different trains on the same track. I have been playing around with both signals for a while and I can't figure it out. I want to make it so only one train is allowed in the roundabout at a time.
Here it is.
https://snag.gy/IwYEKT.jpg
The fast belts on the outside show where I would like the trains to stop, but its not needed.
Only one train goes down each exit so I don't have to worry about multiple trains on either exit.
The roundabout goes counter-clockwise.
Could I get an idea of where the signals should go to allow this?

Thanks in advance.

Here you go:
Yellow = chain rail signal
Red = rail signal

Only place a rail signal if there is room for an entire train in front of the signal.

Wow, it works!
Just curious, what goes though your head when you made this? You did this in under 10 minutes. How do these signals work?

The simplest way is just think in terms of entrances and exits.. Where is my train going to exit and put a regular signal after the exit then put a chain signal before the entrance. After that just visualize each inside path and signal accordingly

I.E If you have 2 exits at a minimum you will want 3 signals. 1 Chain signal and 2 regular signals. If you have a 2way track that merges into a 1 way then you have to remember that your entrance is also an exit and will need a signal across from the entrance signal. Kinda hard to explain but there are a bunch of train tuts on youtube.

Once you get used to it, it becomes second nature.

Check out this video, it goes through all things related to trains from simple to complex and is extremely well made and easy to understand:
https://www.youtube.com/watch?v=3ZiL7_vfJtQ

Only place a rail signal if there is room for an entire train in the space ahead of it. Place a chain signal immediately before any occasion of tracks merging, splitting, or crossing.

Kelderek wrote:Place a chain signal immediately before any occasion of tracks merging, splitting, or crossing.

I don't agree. Placing chains signals in any occasion is bad habit because in many situation they're not needed. You have to know what you want to achieve and think if chain signals are necessary or not.
For me chain signals have 3 purpose:
- prevent blocking lines
- allow train to choose alternative way
- prioritize lines

First purpose is obvious. Stop train before cross if he can't leave it immediately. That allow other trains to go if they have space and prevent deadlocks.

Second purpose is handy when you split rails and train can choose any rail to reach destination. If all rails are occupy then train don't know which will be free sooner or later. So chains signals stop train before split and allow him to go right after one of the line is free.
When we split rails and both of them go to different destination then chains signal is not needed because each train have not alternative way and don't have to wait before split.

Third purpose is handy when you merge rails. Normally when you merge rails you don't need chain signals because all train have one way to go. It's no difference if train enter on merged rails or not. But when you want to one way have higher priorytet then another, you can place chain signal on rail with lower priority. In that way train stop before chain signal and wait until all trains on main line go through.


EXAMPLE


As you can see i placed only 3 chain signals and all prioritize lines.

First chain signal on top-right.
If train arrive from top line and train on loop want to go top, then we have conflict.
Train on top have to enter loop and free line. Then train on loop can go top. So entrance have higher priority.

Second chain signal on top.
Allow train from loop go to bottom exit before train from top enter loop.

Third chain signal on bottom.
The same situation like witch first chain signal.

You have to remember that loop have capacity and increasing train number above that capacity can cause deadlock. For example on loop you have all train from top and another train from top arrive. That train cant enter loop because there is no space and train from loop can't leave because top line is occupy.

I think perhaps you might have missed some signals in the loop, because as you showed in your image I can create a simple deadlock with only two trains:



If the blue train wants to exit to the west and the yellow train is coming down from the north it will block the exit preventing the blue train from ever leaving. Using the chain signals the way I had shown the yellow train would have stopped up at the top where I show the pink, not blocking the exits at all.

Now if there are only two trains this can be fixed by adding a rail signal somewhere inside the loop - probably right in front of where the blue train is stopped in my image here (which I had in my first image). In that case all of your signals would be fine.

Every case is different and I just go back to stressing that video I linked which does an amazing job of explaining signals far better than I can here.

I didn't placed signals on the loop because they depend on how long the train is.

Besides I mentioned about loop capacity. Even if you place signals on loop you still can cause deadlock if you put too much trains. The loop itself is bad design.