I'm trying to understand the junction rules, and translate to simutrans working. We have to distinguish a junction of lines without station, that would be (in simutrans) signalled by plain signals, and a station, where a choose signal would be used.
Choose signal should work just the same as in absolute or circuit block. Make reservation up to the platform or end-of-choose. In old czechoslovak (and austro hungarian) rulebooks, there is a sort of old entry signal, that was probably used to protect the station already in time-interval era. It was electro-mechanical, and operated by the station master - so he knew exactly if the points are set correctly and tracks are clear, just like in absolute block, with no need for telecommunications.
For junctions with simple signals it is a bit more complicated. Simple solution would be to switch to absolute block - default danger, make reservation through the junctions up to the next signal. The rule 59. seems to be some sort of transition between time-interval and absolute block. Otherwise for pure time interval at junction (42) I would expect something like this:
- if there are no junctions ahead of signal (up to the next signal), normal working applies - default clear, < 5 min danger, 5-10 min caution, >10 min clear
- if there are junctions ahead - default danger. All signals around one junction must be connected to the same signalbox. Only one of them can be pulled off (at caution) at any time. Next train (in whatewer direction) can follow after 5 minutes. Clear aspect is not used at all.
- I know this makes quite a bottleneck. It could be improved if the 5 minute interval is kept for each branch (next signal) separately, but I don't know how hard would that be to implement.
However, the idea that trains pass junctions at caution, takes me back to modern (absolute/circuit block) choose signals, especially those with has_selective_choose=1. Usually when train has to take alternative (not-straight) path, it has to traverse switches at lower speed. CZ/SK speed signaling has aspects for 40/60/80/100 km/h, and I used the 40 km/h aspect for choose signal showing the alternative route. I know that the speed would be limited by curvature of the track, but it could be further limited in similar way as in time-interval's caution - half of tracks or signals max speed. And if the correspondent distant signal could show 3rd aspect if alternative route is selected, it would be even better. But consider this as low priority wishlist item
