Looking for feedback: 4-way junction

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dot_sent
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Looking for feedback: 4-way junction

Post by dot_sent » 23 Aug 2019 21:25

Hello everyone,

I've been playing OpenTTD for a long while, but just decided to register here and ask for some feedback on the junction I've developed. I hope I have chosen the right forum for this.

The junction can be seen here: Image

I assume it's not unique, but unfortunately there is no forum search on junction shape :) The closest I could find was viewtopic.php?f=29&t=54368&p=944977&hil ... on#p944977

As far as I can tell, the main disadvantage it has are non-natural turns. However, my trains (normally of length 5) can pass it without much speed reductions in any direction.

I'm using this junction as a basis of the grid network that covers entire map, going through less populated areas without industries, later connecting individual stations to this network one by one.

Do you all see any other problems with or possible improvements to this junction? Thanks!

rowdog
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Re: Looking for feedback: 4-way junction

Post by rowdog » 24 Aug 2019 06:49

I like how your junction looks but I think that all those level crossings will make for quite a bottleneck as you get more traffic through there. I also think that mixing depot traffic into the junction will cause a lot of slowdowns.

I don't really know how to classify junctions but it looks like a variation on the star to me. You can find all sorts of junctions on the wiki.
https://wiki.openttd.org/Star_Junction

JLC1990
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Re: Looking for feedback: 4-way junction

Post by JLC1990 » 25 Aug 2019 00:41

Hi, i see one problem, at those consecutive tunnels you doesn't have any semafors.

dot_sent
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Re: Looking for feedback: 4-way junction

Post by dot_sent » 27 Aug 2019 07:30

Thanks for the feedback!

I likely can remove those depots by changing the default settings. So far I always let my trains run on default maintenance schedule (every 150 days) and this led to situations when a train would take a wrong turn at the junction because it suddenly decided to go for maintenance and the nearest depot was at the "wrong" line. I'll see how much effort it will take to just enforce maintenance at the stations and disable the regular one.

Regarding the congestion when the map fills up - I haven't seen it so far, but I'll keep looking.

Regarding the absence of the signals in the tunnels - yes, I've made a conscious decision not to add them since it would require expanding my junction to occupy even larger space. At the moment the tunnels I have can be safely replaced with the ones with length 8 (and it will even cost less since less terraforming would be required).

JLC1990
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Re: Looking for feedback: 4-way junction

Post by JLC1990 » 28 Aug 2019 13:54

HI, back to that semaphor between tunnels, what about instead of the second tunnel you put that double track above to bridge and put semaphor under it :wink:

dot_sent
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Re: Looking for feedback: 4-way junction

Post by dot_sent » 28 Aug 2019 16:05

Hi JLC1990,

Thanks for the idea- I didn't think about it! Indeed, it will allow the signal placement there.

*Out to modify some junctions in the last game :D*

odisseus
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Re: Looking for feedback: 4-way junction

Post by odisseus » 09 Sep 2019 23:51

I think the depots at each entrance are counter-productive. I understand that their purpose is to reduce the probability of trains breaking down while passing the junction, but a train entering the depot blocks the line just like a broken one. Moreover, the depots are placed in such way that a train that enters one of them would be blocking not one, but two lines 50% of the time.

Now consider what happens in case of a prolonged traffic jam on one of the branches. The trains approaching from that direction will have very low reliability, and the pathfinder will try to service them at the first opportunity. As a result, most trains will enter the entrance depot, jamming one or both tracks in the process, and the rest will enter the junction without servicing and likely break down in the middle.

The proper way to build depots is placing them some distance ahead of the junction, and arranging them in clusters.

Another potential cause of jamming are the block signals that are placed immediately after the entrance. Every signal defines a spot where trains may stop. If the head of a train stops immediately after the entrance, it will block that entrance and possibly the adjacent one.

Actually, this problem is present in most of the example junctions in the wiki. This happened because those junctions were designed before the path signals have been introduced. Back in those days, each train used to occupy not just its own path, but an entire block of connected track between signals. In order to minimize the occupation time, it was customary to make blocks that contain the track split as short as possible, but with advent the of path signals this approach become counter-productive as well.

The nearest signal after a split should be placed at such distance that the longest train which passes through the junction won't occupy the junction tile if stopped at that signal. If your longest train is 5 tiles long, this means that 5 full tiles after the split should not contain any signals.

Lastly, how many trains are going to pass through that junction? Perhaps you don't need such a large one? Perhaps you don't need a junction at all?

_dp_
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Re: Looking for feedback: 4-way junction

Post by _dp_ » 10 Sep 2019 10:03

odisseus wrote:
09 Sep 2019 23:51
I think the depots at each entrance are counter-productive. I understand that their purpose is to reduce the probability of trains breaking down while passing the junction, but a train entering the depot blocks the line just like a broken one. Moreover, the depots are placed in such way that a train that enters one of them would be blocking not one, but two lines 50% of the time.
You have to put a fail-safe depot on every split if you don't want your trains to get lost and jam something else. Making sure those depots aren't used regularly is a separate issue.
That said, making big networks with breakdown enabled is a lost cause anyway imo.

Alberth
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Re: Looking for feedback: 4-way junction

Post by Alberth » 10 Sep 2019 10:54

Nah, just add more track. Breakdowns make that a train needs more space to limit the impact, so a single track can carry less trains. Solution is to add more tracks in parallel.
More track and junction building, more fun :D
Being a OpenTTD developer does not mean I know what I am doing.
Also, other OpenTTD developers may have different opinions.

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