By now, you try to carry all iron ore to a steel mill in one corner of the map, then all the steel to a factory in the other corner of the map and the goods back to a city near the steel mill. Maximum profit, but no nice track layout. I suggest to limit the amount of cargo an industry or city accepts. A steel mill could, say, transform a maximum of 800 ore to steel per month, while a city might accept at most 1 unit of goods per 10 citizens.
Players would have to transport a lot more and to a lot more places...
Some other things that came to my mind:
* highlighting of industries 'connected' to a station (withing catchment area)
* possibility to view the catchment area of a station, especially for complex stations
* statistics of how much cargo is transported from/to a given station, perhaps also by which train (actual units, not percentage of what is produced --> spreadsheet)
* station-overview should include the amount of passengers, goods etc. at each station (again, actual numbers --> spreadsheet)
* more flexible tunnels (not only straight, one might click on one tile with the tunnel-cursor and then hold and drag to another tile with the to-be tunnel being white if valid or red if invalid)
* signals in tunnels (I hate to destroy whole mountains for my tracks, but you simple cannot have a 20..30 tile tunnel in a busy line)
* more than one signal per tile, allowing the maximum of 8 possible signals --> smaller junctions (might be hard to implement, and is rather obsolete *if* pbs is re-enabled)
* marshalling yards - allow carriages to have schedules and be attached and detached to engines. A marshalling yard would be a station with a depot included. If a train arrives with carriages that have a different station as next item in their schedule than the engine, then they are detached and stored in the depot. As soon as a train arrives that goes to the desired destination, the carriage is attached to that train. (quite hard to implement I think)
* redesign of trains (add/remove carriages, change engine) outside a depot --> the actual changes will happen the next time a train enters a depot
* priorities for trains (and priority signals). At junctions with priority signals a lower-rated train would wait to let the fast higher-rated passenger trains pass.
* deadlock-detection would be nice. If a train stops at a green signal, because it realizes that passing this signal would cause a deadlock. Either in cloverleaves or (more difficult) in ore/steel stations (if a station is full of steel trains with 'full loading' orders and no more steel available, no ore train will be able to enter the station and drop ore)... not highly important, but this would make networks less complex.
BTW - don't get me wrong, this already is a great game as it is now, the developers did (do) a brilliant job
