The International Simutrans Forum

 

Author Topic: Absolute block working  (Read 246 times)

0 Members and 1 Guest are viewing this topic.

Offline Vladki cz

  • Devotee
  • *
  • Posts: 2508
    • My addons, mostly roadsigns
  • Languages: EN, CS
Absolute block working
« on: February 21, 2019, 06:31:36 PM »
I have noticed that when train is departing in absolute block mode, it attempts to reserve the track two signal boxes ahead. This is fine on plain double track without junctions, but it is inconvenient on single track with passing loops.

Is that intended behavior? Could it be changed so that the advance reservation is done only if the next section is without junctions?

Offline jamespetts gb

  • Simutrans-Extended project coordinator
  • Moderator
  • *
  • Posts: 18246
  • Cake baker
    • Bridgewater-Brunel
  • Languages: EN
Re: Absolute block working
« Reply #1 on: February 21, 2019, 06:42:53 PM »
Absolute block is not intended to be used on single track lines: token block is intended for this application.

Offline Vladki cz

  • Devotee
  • *
  • Posts: 2508
    • My addons, mostly roadsigns
  • Languages: EN, CS
Re: Absolute block working
« Reply #2 on: February 21, 2019, 08:32:00 PM »
What was the real world (UK) practice? Did all single track lines use tokens? Was absolute block  absolutely limited to double tracked lines?

Offline jamespetts gb

  • Simutrans-Extended project coordinator
  • Moderator
  • *
  • Posts: 18246
  • Cake baker
    • Bridgewater-Brunel
  • Languages: EN
Re: Absolute block working
« Reply #3 on: February 23, 2019, 12:38:59 AM »
What was the real world (UK) practice? Did all single track lines use tokens? Was absolute block  absolutely limited to double tracked lines?

Yes - in the UK, single track lines always (so far as I am aware - very early railways might have differed, and self contained networks with only one train in steam at any one time would of course have had no signalling at all) had to have some additional protection for single track sections. In the very early days, a staff was used: only the train that had the staff may enter the section, and there was only one staff. It was quickly realised that this was inadequate, as this only allowed for trains travelling in alternating directions. Thus, the staff and ticket system was developed, allowing one train to follow another: the idea was that the driver of the first of two trains in the same direction would inspect the staff at the start of the single track section, and receive a ticket, but leave the staff at the start of the section for the next train. This staff and ticket system worked, but could give rise to difficulties in cases where things did not work as expected, and it was not uncommon for a deadlock to arise with the result that it was necessary to send somebody on horseback to fetch the staff from the other end of the section.

In, if I recall correctly, the 1860s a more sophisticated system was invented, the token block system. This was an electrical equivalent of the staff and ticket system: there would be a stack of tokens at token machines at each end of the section. A train would have to have one token to enter the single line section. However, only one token could be withdrawn from the machines at either end of the line at a time, although multiple tokens could be stacked on top of each other at either machine to allow a number of trains to pass in the same direction. There were some variations on this basic idea, but this system remained dominant on single track lines until track circuits were introduced which eventually made this additional layer of safety redundant (although not immediately).

There has been intermittent discussion about trying to model the staff and ticket system in Simutrans-Extended, but this is not workable because either it is very awkward for players to use and (realistically) prone to deadlocks (which would be unmanageable in online games) or it would be functionally identical to token block.

Offline Vladki cz

  • Devotee
  • *
  • Posts: 2508
    • My addons, mostly roadsigns
  • Languages: EN, CS
Re: Absolute block working
« Reply #4 on: February 23, 2019, 01:08:19 AM »
OK thanks for the explanantion.

Are you sure that ticket-and staff was functionally identical to token block? Was there any sort of communication between stations confirming the arrival of the train (and thus clearance of the track) ?
I do not think so. I think it was more like time interval working - the station with staff was issuing tickets in timely manner  (like every 5-10 minutes), and then sent the staff to the other end.

Offline jamespetts gb

  • Simutrans-Extended project coordinator
  • Moderator
  • *
  • Posts: 18246
  • Cake baker
    • Bridgewater-Brunel
  • Languages: EN
Re: Absolute block working
« Reply #5 on: February 23, 2019, 01:15:29 AM »
OK thanks for the explanantion.

Are you sure that ticket-and staff was functionally identical to token block? Was there any sort of communication between stations confirming the arrival of the train (and thus clearance of the track) ?
I do not think so. I think it was more like time interval working - the station with staff was issuing tickets in timely manner  (like every 5-10 minutes), and then sent the staff to the other end.

Staff and ticket was not functionally identical to token block, in that it had a much higher propensity for deadlocks. Its actual workings are described in my previous post. It was developed and used at a time when the fastest way of communicating between the beginning and end of the section was by train. Token block was introduced in the days of the electric telegraph.

What I wrote above apropos being functionally identical to token block is that, if the staff and ticket system were implemented in Simutrans-Extended, either it would be done realistically, but be extremely difficult for players to use and extremely prone to deadlocks, or it would be implemented in a very simplified fashion which would be functionally identical to token block.

There may have been an intermediate stage between staff and ticket and token block when telegraph equipment was used with the time interval signalling system, the telegraph equipment being used to fix the direction of travel: but we simulate that with the time interval with telegraph working method, which I believe we discussed in detail some years ago.