Author Topic: Discussion of new signalling system  (Read 22712 times)

0 Members and 1 Guest are viewing this topic.

Offline jamespetts

  • Simitrans-Extended project coordinator
  • Moderator
  • *
  • Posts: 14774
  • Total likes: 310
  • Helpful: 144
  • Cake baker
    • Bridgewater-Brunel
  • Languages: EN
Re: Discussion of new signalling system
« Reply #175 on: March 08, 2017, 10:57:19 PM »
I think that the signalman would just telegraph to the next section a code asking it to be cleared, and, if it could not be cleared, would set his own section's distant to caution.

As to how it would work in the game, the plan is for there to be an option in each schedule entry for double blocking, so that the train would use double blocking when that schedule entry is the next destination.

If you would like to work on the code yourself, that would be splendid, although the signalling code is somewhat challenging to work on because of its complexity. The main logic can be found in the block_reserver method in simvehicle.cc, although there is also some of the logic in rail_vehicle::can_enter_tile(). Specifying a new type of signal will need to be done in roadsign_desc_t, but you would also need to modify roadsign_reader.cc and roadsign_writer.cc to read and write the new data.
Download Simutrans-Extended.

Want to help with development? See here for things to do for coding, and here for information on how to make graphics/objects.

Follow Simutrans-Extended on Facebook.

Offline Ves

Re: Discussion of new signalling system
« Reply #176 on: March 08, 2017, 11:33:21 PM »
Interesting with the Pullman method. And why would it need double block? Did it have a relative long braking distance or was it very fast?
But still, will it not be to great assumptions on behalf of double block/single block reservations if, say, the Pullman exits at the same route as ordinary scheduled trains does, but due to the pullmans need for two blocks to be free, the other trains having a higher block resolution (only need one empty block) could keep the 'second' block occupied, blocking the pullman?

I will mess around with the files and see if I can end up with something useful!

Offline jamespetts

  • Simitrans-Extended project coordinator
  • Moderator
  • *
  • Posts: 14774
  • Total likes: 310
  • Helpful: 144
  • Cake baker
    • Bridgewater-Brunel
  • Languages: EN
Re: Discussion of new signalling system
« Reply #177 on: March 08, 2017, 11:44:49 PM »
The reason that the Blue Pullman on the Midland Region was double blocked was that it was faster than the other trains using the line at the time, and it would not have been able to stop in time from a distant signal to the home signal. (The line was later re-signalled with four aspect colour light signals so that much faster (200km/h) trains were able to use it without any special arrangements).

I do not entirely understand the question about blocking the Pullman, however; can you elaborate?
Download Simutrans-Extended.

Want to help with development? See here for things to do for coding, and here for information on how to make graphics/objects.

Follow Simutrans-Extended on Facebook.

Offline Ves

Re: Discussion of new signalling system
« Reply #178 on: March 09, 2017, 12:04:22 AM »
Ah ok I see the reason to use double block for it!
I might have misunderstood, will the Simutrans double block setting only reserve two blocks when it cannot stop within one block?
If it will indeed reserve two blocks (no matter the speed) then the effect could become that it gets lower "priority" out of a station than single block reserving trains.

Offline jamespetts

  • Simitrans-Extended project coordinator
  • Moderator
  • *
  • Posts: 14774
  • Total likes: 310
  • Helpful: 144
  • Cake baker
    • Bridgewater-Brunel
  • Languages: EN
Re: Discussion of new signalling system
« Reply #179 on: March 09, 2017, 01:18:56 AM »
I have to say, I had not thought in detail precisely how it would operate.
Download Simutrans-Extended.

Want to help with development? See here for things to do for coding, and here for information on how to make graphics/objects.

Follow Simutrans-Extended on Facebook.

Offline Vladki

Re: Discussion of new signalling system
« Reply #180 on: March 25, 2017, 05:04:07 PM »
I think that double block in james' and ves' ideas are something totally different.

What James shows as an example for blue pullman, is just an early attempt to transition from 2-aspect signalling to 3-4 aspect signalling. With the first distant signal meaning "preliminary caution" although it was not distinguishable from normal caution.

What Ves attempts to do is a special signal used in the following scenario: on czech/austrian/german and probably also swedish railways in earlier times, with absolute block signaling (or its bidirectional equivalent), stations had only one start (departure) signal for each direction (or branching line). This signal was usually standing beyond of all switches, in place where all the tracks were already joined together. Trains were supposed to stop before the switches. The start signal showed clear only if the appropriate line is clear, but did not show from which track was the departure path set up.

So the signalman had to personally show which train is allowed to leave. Later a special (cheaper) signal was designed for it. It was pulled off to allow shunting (start signal at danger) or departure (start signal clear). Later color light version had different aspects for shunting and departure: https://cs.wikipedia.org/wiki/Vlo%C5%BEen%C3%A9_n%C3%A1v%C4%9Bstidlo_a_uz%C3%A1v%C4%9Bra_koleje The departure signal - whether mechanical, color light or hand signal, could not be given if the main start signal was at danger. Thus they make two block signal of sort.

Later the signaling logic was combined in one and each station track got its own start signal, in similar way as it can be used in simutrans now. However, I think this method of signaling could be useful in the game for stations, where lines with different signaling methods meet. You could put the new double signals at all tracks, and standard signals at the lines beyond the switches. One line could be token signaling, another track circuit, and so on. There would be no need for passing loop outside of station as show in some previous examples.

I think this could be partly achieved by extending the current behavior of signals at the end of platform to distant signals. Now if there is a signal exactly at the end of platform, the train is waiting for clearance on its stopping place, continues to load - it does not move to the end of platform until the signal clears. Would it be a big change to make this apply also to distant signals at end of platform? A train that has stopped in the station would wait for clearance on the platform, until the start signal further ahead clears. I know that this would not work for train that is driving through the station, but it would be nice as a partial workaround.



Offline Ves

Re: Discussion of new signalling system
« Reply #181 on: March 25, 2017, 10:35:37 PM »
Vladki, I think you are right in your description about the difference off James and my version and also in the way the two block signal would be useful.

I have not yet started, only looked in the code at the places James mentioned and tried to get an overview!

Offline Vladki

Re: Discussion of new signalling system
« Reply #182 on: March 26, 2017, 11:25:13 AM »
I have found a very nice information about signalling at ffestiniog railway:
https://www.festipedia.org.uk/wiki/Signals_Contents (more links)
https://www.festipedia.org.uk/wiki/Category:1872_Rule_Book

It seems that they used the same signals as sweden in early times - T signal and disc (plate) signal. They were used in combination with staff & ticket, and later with ETS (electric train staff - i.e. token_block in simutrans). Staff & ticket is in essence a sort of time-interval working on one track lines - tickets are given in time intervals, staff governs the direction. So the t-signals should be used with time-interval-with-telegraoph (as an aproximation of staff& ticket), as well as token-block (ETS).

They do not use the term T-singal, but this is what applies: https://www.festipedia.org.uk/wiki/FR_Signals
Quote
Each intermediate staff stage station had a centrally located, double-armed, semaphore signal that served as a 'block' Signal. The semaphores acted as a combined Stop and Starter signal, although they did not denote the actual stopping position, they denoted 'Stop and Wait for Train Staff or Train Staff Ticket'; this also applied to the pair of double arm semaphores at Old Dinas Junction at Glan y Pwll. The two arms served up or down trains according to the side of the post.
So I think the T-signal was really used only to signal departure (starter signal). The Ffestiniog railway is a narrow gauge railway - very twisty, deep in forests. In some stations it might be impossible to see the central T-signal from the farthest points, let alone some safe braking distance ahead. (see https://www.festipedia.org.uk/wiki/Tan_y_Bwlch) For protection of stations, level crossings, tunnels, etc, the disc/plate signal was used. It could be operated remotely (mechanical wire), so it could be put in greater distance from the station building, see https://www.festipedia.org.uk/wiki/Disc_Signals

Also, what I descibed in previous post - a single start signal for the whole line placed ahead of all points - is the case not only for CS/SWE, but also for FR. See the photo at https://www.festipedia.org.uk/wiki/Signals_controlling_section_entry. There is a normal semaphore at the exit path form station. It was apparently interlocked with ETS - it could be pulled off only if the matching token was put in a drawer slot, and later handed over to the driver of train that was about to depart.

In both arrangements (T-signal, or start signals at both ends), the trains obviously had to stop before Fouling point, in order to keep the switches (and movements on other tracks) clear.

The arrangement with double-block signal, would also solve the problem when a train in token/one-staff mode keeps the reservation backwards up to the signal. If the signal is at each track, the junction is kept blocked, which is a problem if there are multiple lines joining. It would also help with time interval signals where trains are not allowed to go full speed over junctions. Start signal beyond junction would solve that.

A possible (but still partial) coding solution might be what I suggested before - that trains wait for clearance on the platform even if there is a distant signal at platform end, or that they wait for clearance at nearest signal ahead of platform. Even if it is further out than sighting distance, or beyond some switches. However neither of these would work for trains that are not scheduled to stop in the station. That would need the double block signal or T-signal.
« Last Edit: March 26, 2017, 04:10:38 PM by Vladki »