'safe' PBS

[m3henry]

I have recently had a speight of PBS related crashes.
So I had this idea:

Why not have a PBS system that reserves the tiles until the train leaves the junction instead of when the train exits the tile in-front, this would reduce the efficiency of the junction, but mean the train is very unlikely to have a crash, or be stuck trying to reverse at a signal or end-of line section.

Is this a inplementable feature or is it not.[/list]

[WWTBAM]

but that removes a large part of the useful ness of PBS as you said, so PBS is only useful for junctions where the trains dont need to cross each other like this lXl

[DaleStan]

Can you show us a junction (translation: "savegame and configs") where PBS breaks, but your proposed changes would prevent the breakage?

[JGR]

This wouldn't actually help safety that much, because once a train is already onto a junction it would crash even if the train had not unreserved its previous tiles. Existing crashes woud probably still occur. (PBS crashes are exceedingly rare, unless you have lots of trains stuck at signals and reversing).
Additionally, this change would make unreserving tiles behind the train as it leaves the junction much more complicated and more likely to introduce new "track unreservation" bugs.

A far more useful 'safety feature' which would more efficiently catch certain PBS bugs would simply for a train to stop and display a stop message (similar to: train X tried to reverse but cannot do so safely...), if it is in a PBS junction and the tile it is about to leave does not connect to a reserved tile in the appropriate orientation in the next tile.
ie. If there is a case where part of a train's reserved path is unreserved, because it was overwritten by another train, etc., instead of continuing blindly (and unsafely) it should just stop instead.
Most of the PBS crashes I can think of happened when a trains path in front of it was unreserved due to erroneous behaviour of reversing trains elsewhere or other bugs, and another train reserved a path across the previously reserved path of the first train.

Just my thoughts on the matter.

JGR

[m3henry]

I know, but during that speight of crashes, savegame lost, I was getting a lot of messages, so I couldnt keep track of all the trains that were getting stuck. then it would take two TTD months for the crash messages to come through.

This feature (if possible) would allow for user free reversal without having to re-reserve track