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Author Topic: Choose and Two block signal behavior  (Read 267 times)

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Offline hreintke

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Choose and Two block signal behavior
« on: November 24, 2018, 04:51:22 PM »
Question is about combining two block and choose signals.

I have a multiplatform railstation on which from two sides trains arrive.

In order to make sure all platforms are used, there is a choose signal.
In order to make sure that the intersection is not blocked, there are two block signals around it.

Both the Lines from the trains have their route points on the right platform.

When that platform is in use, the two block signal doesn't become green when another platform is available.

Expected that the choose signal behaves like a normal signal, becoming green when a route to any of the platforms is available.
But it only becomes green when the actual routepoint is available.

Is this the way it is supposed to work ?
If so, what combination of signals can achieve both choose and intersection saveguard ?

I attached a picture and small pak64 savefile which shows the issue.

Offline Vladki cz

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Re: Choose and Two block signal behavior
« Reply #1 on: November 24, 2018, 05:52:36 PM »
Just remove the choose signal, and replace the two block signals with choose signals.

Offline Ters

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Re: Choose and Two block signal behavior
« Reply #2 on: November 24, 2018, 06:55:18 PM »
In addition, the signal out from the station seem to be to be more likely to cause harm than good. In fact, if there are three or more trains stopping at the station, it may deadlock completely. So remove that too. The normal signal at the bottom might cause similar problems, but I can't tell from just this image. Signals should in my opinion always be a train length away from junctions, so that trains don't stop blocking the junction. It is usually better for the train to stop earlier so that other trains may pass the junction in other directions. (Pre-signals can mitigate, but there are usually better solutions.)

Offline hreintke

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Re: Choose and Two block signal behavior
« Reply #3 on: November 25, 2018, 12:58:33 PM »
@vladki Thx, works. Disadvantage is that the choose signals on the new position also have effect on stations further on the line. Need to check further on that.

@Ters  The signal out from the station is there to protect for a deadlock on the intersection. That is why it is a two block signal.
For the bottom signal, with the two block signal ahead of it, it should be no problem having the signal close to the intersection.
But now they are updated to choose signals, need to relocate them also.

Offline Ters

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Re: Choose and Two block signal behavior
« Reply #4 on: November 25, 2018, 03:01:50 PM »
The signal out from the station is there to protect for a deadlock on the intersection. That is why it is a two block signal.
Yes, but it risks blocking the intersection between it and the station.

For the bottom signal, with the two block signal ahead of it, it should be no problem having the signal close to the intersection.
But if trains can never stop at a signal, why then have a signal at all?

Offline hreintke

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Re: Choose and Two block signal behavior
« Reply #5 on: November 25, 2018, 04:21:17 PM »
Quote
Yes, but it risks blocking the intersection between it and the station.

Did not think about that. Thx.

Quote
But if trains can never stop at a signal, why then have a signal at all?

The train doesn't stop at the signal itself but at the two block signal in front of it.
By having the signal close to the intersection,the block reservation of the intersection is cleared as soon as the trains has left it.

Do need more thinking on this. The reservation at a choose sign (looks like) is the full path to the station.
But now there is/can be a choose sign on the track to a station it is not meant for. 


Offline Vladki cz

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Re: Choose and Two block signal behavior
« Reply #6 on: November 25, 2018, 04:34:28 PM »
You have to put end of choose signs on exit paths to other stations. Reservation are cleared tile by tile, so you don't need to care about that. Just put the first signal far enough so that the longest train will not block the intersection.

Offline Ters

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Re: Choose and Two block signal behavior
« Reply #7 on: November 25, 2018, 08:16:18 PM »
The train doesn't stop at the signal itself but at the two block signal in front of it.
Exactly. And the same effect can then be created by using a normal signal rather than a two-block signal and skipping the other regular signal. (The new priority signal / non-greedy two-block signal would be different, but then the deadlock issue in the main intersection would be in full effect.)

Another possible issue with the depicted station is that two trains from one line may end up waiting at both platforms, preventing trains from the other line from using it. It won't be a problem if none of the trains wait for a load, but if that was the case, I would rather give each line its own platform and avoid the entire chose signal "chaos". When multiple lines wait for a load from the same place, I either section the station into distinct areas for each line with their own chose signals at entry and end-of-chose at exit, or give each line its own platform and a dedicated section of track before the station where trains can wait for their platform to become free without obstructing other trains. That section of track has to be long enough for all but one of the trains serving the line (the last one occupies the platform) if one wants to be absolutely safe (can give stuck traffic warnings if waiting times are long, though). Or just build different stations for each line.