Strategies for a busy network

[Lord Vetinari]

It's not really a request for help, so I post here.

I started a new game because I wanted to build a very large passenger network on a big map, and to test how it runs.
So, I plopped a gigantic city (after nine game years it's size is 238.634), a lot of other small towns (total region population 814.573, 187 cities - didn't counted them while I was plopping, I think I overdid a little ) and slowly built, along the rest of the passenger network, a metro system inside the big city, vaguely inspired by the Chicago L.

By the way, even now that almost every town is connected to the network, Simutrans is handling everything pretty well, I didn't see any serious framerate drop. Good work!  
The company itself is insanely profitable, but that was expected, with all those destinations.

Back on topic, I have a downtown loop which is used by 6 out of 9 metro lines. Well, the tracks do form a circle (or, rather, a rectangle), but actually none of the lines make the full loop and turn back, as the real CTA L lines do.
These are the actual lines routes:



The loop works smoothly 99,9% of the time (well, there are quite few trains that have to wait at a red signal, but that's normal on a buisy system); in the 0,1% left, a huge gridlock happens, something that requires to send half of the trains to the depot or, if it's too late even for that, to reload a previous save.

In 9 game years it happened only two times, so it's not really a big issue. I know why it happens: since there is no practical way to keep the trains of the same line at a regular distance, it randomly happens that all the trains sharing the tracks downtown converge on the loop blocking everything.
I'd just like to ask you what you would do to improve that part of the system, more like a theorical discussion than an actual help request.
I don't have room to add more tracks at the same level of the old ones and I can't stack a second level of tracks on top of the old ones due to some complex flying junctions; nor it is needed, I think, as half of the time the trains don't even have to wait at signals. I think that there is still enough room to roughly double the number of the trains of all the lines.
I tried with pre-signals on the tracks that enters the loop, but it didn't help much. Actually it made things worse, as it practically blocked all the secondary branch because the trains on the loop always had priority.

This is the diagram of the tracks, to help the discussion. RH driving, red dots are standard signals.

[prissi]

You can try more signals, that would allow to fit one or two more trains on those tracks. Apart from that there is probably not much you could do. (And a savegame might have bee easier for me than all those drawings ... )

[TheMacpau]

I find using measured waiting areas very helpfull in keeping things moving when using double track stations with no passing place.

So if your using 6 length trains you have where the S is a regular signal and - is a track square
----(station)------S------S----...etc

You appear to have some signals infront of your stations but I can't tell how far away they are, remember stations have their own invisible signals.

However in your case I think the blockage might be due to there being signals too close following a junction so a train doesn't fully pass through causing it to get stuck in the junciton. This will usually clear provided the train in front moves off but if there is a second jam preventing the first train moving, you quickly get some unholy mess. (at leasts thats what usually happens when I try to be too clever with the junctions)

[Combuijs]

I would redesign the loop, especially the pink and the blue line. I think these lines are causing the problems. If they don't each other, things might go better.

[Lord Vetinari]

Thank you for the answers.
I'm using and old version of the japanese el rail add-on, I need to find it before I can post the savegame. If I load it with the new version of the add-on some weird graphical glitches happens.

Trains are five tiles long, and, since I set 4 tiles of coverage in Simuconf, there are usually eight tiles between a station and the next one (remember, I was trying to build a metro inside the city, it's not a regular network. I tried to have the best coverage along the tracks; sometimes a little bit of overlappig was necessary, so the distance between stations can be of seven or six tiles in some part of the network. I know that probably Simutrans wasn't ment to be used this way, I was just making experiments).
So, there is room enough for just a single train between stations. The signals are in the tile before a station, so when the loop is very buisy I can use it at maximum capacity with a train loading/unloading at the station and the next one waiting on the track just outside it, which leaves the previous station free for another train.
The diagram I made is accurate in terms of distances (ok, I admit that I like to waste time making maps )

[prissi]

Well, you can have signals on every tile, even within the stations. Thus you can fit more than one train between two stations. That might help to push the deadlock further. About one train further.

[TheMacpau]

Would you then not end up with trains across junctions prissi? A bit like stopping in a hash box at a road juntion, it snarles everything up.

[Lord Vetinari]

I didn't know this. So, I can put a signal in the middle of a platform and a stop at that signal doesn't count as a stop at the station?

[DirrrtyDirk]

As long as you don't put a waypoint on the station, yes, that works (or at least it did, last time I experimented with it... ~2 weeks ago or so).

[Lord Vetinari]

So, if the train is scheduled to stop at that station the signal won't work. Well, it's a good thing to know for next games.

[DirrrtyDirk]

It might actually even work then, depending on the size... but usually platforms are about the same length as the trains... so... oh well, just go ahead and try it, and you will see if it works the way you want or not.

[jellyman]

Also consider larger gaps between signals on the branch lines, as this will increase the minimum spacing for trains arriving from these branch lines onto the main loop.

[Lord Vetinari]

I just read an article about longblock signals (which I never understood well) and they may be the answer for correct spacing of trains, at least on the branches that are used by a single line.
I made a test track and it worked perfectly with four trains.
I suppose i'ts not that easy when many lines share the same traks, but for me it's a good discovery.