A modder by the name of AzzerUK has claimed to have modded out the disconnection timer, allowing him to play "offline indefinitely".

The question of how you save is still the issue though, as the mod doesn't allow any saves or syncs, as you need to be connected to the server to do those functions.

While it's no real offline single player, it shows that there are tweaks that could be made which could open the door to some sort of offline mode.

AzzerUK also tweaked with the code, allowing the ability to edit highways anywhere, even outside of the city boundary.

"This shows that highway editing will be easily possible, AND that editing outside of the artificially small city boundaries should be very viable too, potentially (since you can place roads and rails that snap anywhere on-screen)," writes AzzerUK.

Check out the Reddit post.