Z-levels

[L. Spooner Inc]

I'm curious whether any thought has been put into adding Z-levels to the game. While it would probably require a major engine overhaul, long-term it opens a lot of new possibilities, and fixes some of the current problems around things like boat tunnels and underground viaducts. You'd probably have something like five Z-levels: deep underground/underwater (-2), underground/underwater (-1), surface (0), low/VFR sky (1), high/IFR sky(2). It would also create opportunities to do for planes what TTD currently does for trains with the creation of ATC beacons to avoid mountain ranges and hills, controlled airspace around airports limiting flight volumes, and so on

[acs121]

With patches we already have tunnels under water.

However you're not the first one to request underground stations or stations on bridges as an example.
Lots of people already did this, but yet nobody found a real solution, or started development.

[L. Spooner Inc]

At Cataclysm:Dark Days Ahead, they organized a Kickstarter to create a development budget, then offered bounties on specific problems or desired changes. The reason I mentioned it is this is how Z-levels were eventually implemented for C:DDA.

[acs121]

Although I know people from TT-Forums are here because they like the game and would like it to be improved, I don't even know if starting a Kickstarter page to fund development is gonna do something.
You need to realize that OpenTTD is just a plain recode of TTD dating from 2006. It doesn't mean there's no hope. It simply means that we'll have to do with lots of difficulties, or even the fact that we might not even find a way to make it compatible with other savegames.
This being said, again, you can still be hopeful. Try to travel back in time until 1995 to tell Chris Sawyer that in the future, people developed at least a thousand of add-ons (NewGRFs) for his game.

[kamnet]

I'm curious whether any thought has been put into adding Z-levels to the game. While it would probably require a major engine overhaul...

Yes, it has, and yes, it does.

Several years ago one person started trying to implement multiple levels, but when their work wasn't immediately accepted into the master code (which no code ever is without rigorous testing and ensuring it will be completely compatible) they abandoned both the project and the community. More info on the patch at http://forums.ttdrussia.net/viewtopic.php?f=17&t=3932 and you can also test out one pre-compiled binary at viewtopic.php?f=33&t=65526

[acs121]

Jesus, the russian community is capable of things I didn't even imagine. I thought it was resumed to stuff like SpringPP etc.
I might give it a try although the precompiled version seems really old (1.3.0).

[Expresso]

The problem with multiple levels is that:
1) you need a proper means to store it;
2) that means must not impact performance too much;
3) that means must not consume too much memory, and especially not waste it;
4) the user interface needs to be adapted to account for underground levels;
5) saved games need to remain compatible;
6) appropriate graphics need to be provided.

Implementing this is going to be a mamoth job. Why go for this while there are so many more thing that need attention?