So, I have 2 train routes for exports, highlighted for visibility:
- A cement train that runs between the red line (at the end of which is a loading station for cement) and the customs house at the far end of the green line
- A gravel train that runs from the aggregate loading station at the end of the blue line to the same customs house
Here's the behavior I want:
- When returning from the green route, a train has right-of-way to return to its loading station
- If a train arrives at the intersection from the red or blue route, it should proceed only if there is no train on the green line; otherwise, it should wait until the green line is clear
I'm not entirely sure how semaphores work and no combination of them seems to do the trick. I get trains unable to return from the customs house, trains colliding, or trains forever deadlocked at the junction. I've watched/read like 3 different tutorials and I'm still not sure what I'm supposed to do.
The track is divided into sections by the signals. Only one train can be in any one section.
Some critical sections you don't want trains to enter unless they can exit also, like a junction. Wouldn't want the train entering the junction and then sitting there and blocking it for other trains. So there's a normal signal (single arrow), which allows trains to pass if the following section is clear. Then there's the a chain signal (double arrow), which the train will pass only if it can also exit, i.e. not only is the directly following section clear, but the one after that one is also clear, meaning it can pass through without stopping.
In practice this just means: put a chain signal before any junction or other section you don't want trains to stop. Put regular signals in front of sections the train may stop in. Make sure any section that trains might stop in (i.e. that has a regular signal, not a chain signal, before it) fits a whole train and is a straight line section that couldn't possibly block another train (except trains queuing behind it). Make sure you don't have too many trains, you always need to have a free section somewhere.
This make sense, thanks!