simcity-2013
I've heard of people plopping multiple train stations to get more people into the city. But from my experiences, trains only stop by the closest station before making a uturn back to the region.
Other stations that follow rarely if ever get a train to stop (waiting times go up into the hundreds)
I want to confirm that this is a bug and ask if there are work around. I have not found a reliable one.
What you are seeing is working as intended. Not all cities within a region will be able to share all things but they are eventually able to share most things. The most limited of what can and can not be shared are going to be water, sewage, power and garbage. These are limited by physical roads. This is where you get your cluster or sub-region as you have noted. The best way to tell which cities will be able to share these resources is to see which ones are connected by road as roads are needed to transport these materials.
In the early game this can also hinder almost all resource transfer. You can eventually unlock things like a trade port that can use roads or rail or water to transfer resources locally or globally. There are also additional methods for the transportation of people and such via ferries and the like. The last thing, that jumps the final gap, is an air port.
These things together will let other cities be more connected but it should be noted that anything that requires a road, as mentioned above, will never be able to get to another city that does not have a road connecting to it.
EDIT: Found out last night that gifting also requires a connection between the cities. Even the act of sending money from city to city required at least a rail connection between the regions. I have not seen if ferries or air ports will fulfill this requirement and will update here when I figure that out!
Great Works are region wide as well. If you unlock a great work like the solar farm in one sub-region you are then capable of building that great work at any site on the map. However note that getting resources to a remote location may be a bit of a challenge.
This also works with other unlocks that claim 'region wide' like the upgrades to City Hall. Even though the cities are not connected in any manner people starting up cities in other sub-regions or clusters have access to 100,000 bonds for instance.. Smelting plants and the like. So it does appear that development unlocks also jump over the bounds of a solid (or even liquid) connection.
Before you can begin building a great work, the project for each great work will need to be researched in a city that has a university. This research fee can only be paid by the mayor that has the university in their city. It would be possible for the other cities to gift the money to the city that pays the bill though.
Once construction has started on the great work, each city has their own controls for contributing to the creation of your region's great work. To enable your city to send resources to the great work, you will see on this screen that underneath each resource is a 'power button' (it looks the same as the power buttons to disable buildings). Turn this on and you will start sending resources to your great work site.
To send resources to your great work, zoom out to the region view and click on the great work site - this will show you a status screen detailing each of the resources required to build the great work and the quantity of each resource that has already been supplied.
Best Answer
It certainly isn't the case that the trains stop at the first station before turning back. Even a quick mock up city demonstrates this as per below;
This is in a city plot that has one rail track leading into the city, which I have then extended along the top edge of the map and placed a train station in the top left and top right of the map.
The train will arrive in the city, go straight through the closest station to the station at the end of the line, pick up passengers, and then stop at the other station on the way out of the city to pick up more passengers.
Best guess is that there is another issue causing this problem, most likely relating to how the AI is routing the trains around. There are multiple instances of other similar issues where resources were not correctly moved around the map because of the game's priority system or you've simply got too many passengers going to one station and not enough passengers heading to the other.