Passenger Trains

With the future introduction of larger maps it could be an idea to have multiple cities. Adding a passenger train connection between them could result in giving a small boost to population (simulating workers from one town going to another) and also adding a minor logistical challenge.
And it would also look nice. So far the impact the industry has on cities is rather minimal.

Mabye a unity boost by housing tier or it lets them share commodities without connection to one big block of housing to simulate people traveling to another settlement to shop.