Rooting for the addition of Singapore map as well!
Singapore currently has 5 lines serving 106 stations in operation, with 3 more coming in the future serving an additional 48 stations. While the older lines are mostly above-ground with about 1/3 stations underground, the newer lines are mostly, if not entirely, underground (e.g. Downtown Line is fully underground).
Some unique challenges posed for the Singapore train lines are:
- The North-South Line (NSL) had to cut through a hill or go under ground level at certain sections of its line (multiple passable obstacles).
- The Downtown Line (DTL) had to go from side-by-side to vertically-stacked at one of its station because it was squeezed between a major canal and the deep foundation of nearby buildings (impassable obstacles).
- There's a large reservoir in the middle of Singapore, which so far the government is not allowing any tunnels to go underneath it (large impassable obstacle). This causes all train lines to circumvent it like a giant roundabout.
- Recent upgrade of signalling system for the older lines resulted in frequent massive downtimes during peak hours.
- Limit land capacity also limits the degree of bend possible for tracks, making it that stations have a minimum distance apart, and you can't link two stations that are too close for creating tracks in-between.
I see potential new game mechanisms or choices here, such as technological upgrades to improve train speed and pick-up/unload efficiency, large geographical limitations such as specific, large areas that are marked as impassable to above- or under-ground tracks, minimum-degree of bend for tracks so that it is not possible to link a trio of nearby stations in a triangular track formation (i.e. They must be circular, not straight lines, and if the circular lines cannot be fulfilled because of neighbouring impassable areas, then this line cannot be built).
More info below on Singapore's train system: