@isidoro – Agreed, but as far as I know the game isn’t yet available on mobile devices (not sure their CPUs would cope with the pathfinding?). Much of the UI would need overhaul to make it usable on touch devices – eg. the small icons in the sidebar would probably need to be bigger, and the number of pop-up windows would need to be significantly reduced too I think.
@gGeorg – What if there were a few different game modes to choose from instead? So, for example, “Sandbox” mode could start with no dirt tracks and the user would have to connect things up at their leisure, a bit like “train table” mode in the game “Railroads”. A “Fever” mode would have the dirt tracks, but allow them to be deleted, and a “Brutal” mode (for want of better word) would have protected dirt tracks (and medium tracks between cities to encourage car ownership and use). That would give rise to 3 completely different types of gameplay, simply by tweaking what happens with the dirt tracks (main lines).
As for people disappearing from trains, etc., I would approach that with two flags on agents (people). The first, “Protection flag”, is set when they join a line (waiting at a stop or on a vehicle) and protects them from despawn. The second, “Reroute flag”, is only set if their target building is destroyed while the Protection flag is set (otherwise they are not on a line and can be immediately despawned or re-routed). When exiting a line (including transition between lines) the Reroute flag is checked and if necessary they are re-routed or despawned; otherwise clear the Protection flag (if they are transitioning to another line, I assume the Protection flag would be set again once they reach the stop where they will join that line).