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[Partly fixed] Expansion of city may obstruct navigable route

Started by [C] Ranran, June 27, 2020, 11:31:06 AM

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[C] Ranran

I saw it happen


Also, as reported in another thread, the convoy caught in this bridge cannot get out of it without removing it.

Ronin1996

You might want to try expanding the road a little bit and see if that helps. As for the convoy, I can't help you sorry.

jamespetts

This has been reported previously, and I spent a considerable time looking into it. This is an extremely difficult problem to solve because of the way in which the automatic road building system builds bridges: there is no way (at least that I could find) of causing this system to build double height bridges (I spent quite a few hours looking into this): the problem is that it needs an extra tile for the ramp, and that would have major and extremely complex implications for the whole system of building city roads. So, without very major changes to the city road code, either cities build no bridges, or they build these low bridges.
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Sirius

Iirc, standard had just fixed a quite simmilar issue half a year ago or something like this by artificially flattening the terrain and then building a bridge with slopes on top of it.
In standard the problem was that towns won't build any bridges over rivers if there is a half-height slope involved (which would still be better than the obstructive behavior)

jamespetts

Quote from: Freahk on July 22, 2020, 01:50:44 AM
Iirc, standard had just fixed a quite simmilar issue half a year ago or something like this by artificially flattening the terrain and then building a bridge with slopes on top of it.
In standard the problem was that towns won't build any bridges over rivers if there is a half-height slope involved (which would still be better than the obstructive behavior)

Interesting - can anyone find the commit number in Standard so that I can investigate incorporating this?
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Vladki

Maybe this one?
r8911: city more strongly attempt to build double height bridges over navigable rivers

While looking for that I found this which sound like a bug I hit in extended too:
r9084: enable bridge starting at tiles with road & tram

   

jamespetts

Quote from: Vladki on July 22, 2020, 07:04:58 PM
Maybe this one?
r8911: city more strongly attempt to build double height bridges over navigable rivers

That is very helpful, thank you. I have now incorporated this and it seems to work. I have modified it so that single height bridges can be built over public rights of way that have not been used either in the current or the last month.

QuoteWhile looking for that I found this which sound like a bug I hit in extended too:
r9084: enable bridge starting at tiles with road & tram   

I have also incorporated this - thank you.
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Sirius

Quote from: jamespetts on July 22, 2020, 08:28:45 PMI have modified it so that single height bridges can be built over public rights of way that have not been used either in the current or the last month.
Great!

jamespetts

Can I check whether this can be recorded as fixed?
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Sirius

I guess it's solved for rivers and canals. At least I've not seen this kind of obstruction anymore.
Real water is a different thing though. There had been some obstruction of this kind after the fix.

jamespetts

Quote from: Freahk on July 29, 2020, 09:09:31 PM
I guess it's solved for rivers and canals. At least I've not seen this kind of obstruction anymore.
Real water is a different thing though. There had been some obstruction of this kind after the fix.

This is more complex, since there is no sensible way to determine whether what is being obstructed is a thoroughfare or not.
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Sirius

I am sorry to say this, but it just happened again :(

freddyhayward

Really, this needs to be stopped entirely. No bridges is better than bridges that regular bring the entire global shipping network to a standstill. This is yet another case of half a feature being far worse than no feature at all.

Sirius

In principle, I agree with you, but in this case it's just a bug, not an issue with the design.

In relation to "real" water, I'd always require the cityrowth and industry chain connection system to build high bridges.
Same goes for bridges over roads.
The only case where the system should be allowed to build low bridges is in cases where we know that is definitely won't cut any existing connections.
These cases are initial map creation, unused waterways and unused roads.
In case of "real" water, we don't know, so the system should assume it's used.

freddyhayward

My point was not that disabling bridges entirely is desirable, but just that it would be preferable to the existing behaviour, assuming it can't be trivially fixed.

jamespetts

Thank you for your report. Is anyone able to upload a reproduction case in which this reliably occurs at a specific date and time in the saved game? I assume that the canal had had shipping traffic in the last month?
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Sirius

Quote from: jamespetts on August 18, 2020, 10:04:03 PMIs anyone able to upload a reproduction case in which this reliably occurs at a specific date and time in the saved game?
No. It happened once after many years and I have no idea what has caused this.

Quote from: jamespetts on August 18, 2020, 10:04:03 PMI assume that the canal had had shipping traffic in the last month?
Definitely. There are quite many ships running along that canal.

jamespetts

I am not realistically likely to be able to find this problem without a reliable reproduction case, I am afraid.

If anyone can upload one, I should be very grateful.
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Sirius

Should be moved out of the solved section though.

jamespetts

Quote from: Freahk on August 27, 2020, 11:09:52 AM
Should be moved out of the solved section though.

I have moved it out of the solved section and added [Partly fixed] to the title to indicate that the original reproduction case has been fixed.

If anyone can produce a reliable reproduction case for this occurring again, I should be grateful if people could post this here.
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