This is what I wanted for RT4, but it didn't happen in SMR. So, here it is again. I like the graphics for RT3 and wouldn't mind SMR's graphics and ability to push scenario aside while laying tracks. I like the city based design in the original RT and SMR, but not the city limitations in SMR. So here are my thoughts:
Towns - are placed at the start of a game as per the scenario design or whenever a new station is placed outside of a city radius. Any station in a city radius will have access to all cargoes available to that city and any deliveries to that station will be available to all structures in that city.
City - is created at start or whenever a town achieves a minimum size. These cities control all land in their radius and take priority over towns. No piece of land can be in two different town/cities. City priority is based on age at time of becoming a city followed by nearness. Town priority is based solely on nearness.
Houses - the demands and output of houses, churches,retail, bakeries, etc will be aggregated for all units in the radius of the City/Town. All cargoes will be kept at the city center or some other central location.
Industry/House Demand - All units will creat demand if less than 2 (or whatever) years supply is present in the City. Demand will be a function of supply on hand, at a max with zero units and with no demand if 2 years of supply are present. Inventory of up to 2 years will be frozen and not available to be shipped elsewhere.
Output - Up to 2 years worth will be stored at the producing unit (or central location). Excess will be lost unless a station exists and it has an appropriate storage facility - silo, cold storage, etc. Each facility will have a fixed capacity, with multiple units of the same type allowed. Excess may also be stored at a user unit, but is subject to decay or being shipped elsewhere.
Industry/House - Industry needs workers. 2 house units supply one small industry. one house supplies one small raw material producer; double for large units. Industries that lose money for a set consecutive period will close. Industries closed for a set period will go away; however, raw material producers will not go away unless depletion rules are added. Industries that are profitable will never close or go away unless depleted or become outdated.
New Industry - will only go to a City/Town with excess housing units. Closed industries (not raw materials after some period of time) still require their houses. These houses will have reduced demand and supply fewer passengers/mail.
New Housing - will go first to a rural/town/city area with no excess housing, then to a rural/town/city with excess based on a random function giving priority to areas having the lowest unemployment. Housing growth will be a function of country, territory and excess housing rate (unemployment rate).
Immigration - countries may generate extra one way rail traffic due to immigration/migration. One house will be created/destroyed somewhere in the affected country(s).
Rural - only raw materials may be located in rural areas and no housing unit need be initially present.
New Industry 2 - The type of new industry placed will be a function of the current profitability and inventory of existing and non existing industries, unmet demand for its products and supply of raw materials.
Production - production stops when storage capacity is reached. Cargo only leaves to go to a station or a train. Trains only pick up to meet a specific demand. All loads have a specific destination and once loaded, that destination loses inventory space. (In the event of non arrival, it gets the space back).
Unit Cargoes - to simplify specific destinations, all cargoes will ship in full units. Later larger cars will carry more than one unit. A town/City will always protect one unit of cargo from being shipped if that cargo is demanded in that geographic unit.
Cargoes can still travel over land or water without trains, but only to a specific location that has a demand, the same as for the railroads.
Station size will not affect the size of the City or town radius. Station size will affect passenger handling and desireability (how many trains can load/unload at one time and how fast). Rail yard size will do the same for other cargoes, as will post office size. Engine facility size will affect engine servicing. Telephone/telegragh will affect track useage between stations. The better the signal/communication systems, the closer trains can travel together. (Oh, how I loved the working signals in RT1, but why are they less fun in SMR.)