system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why are alot of train stations in major cities (mostly north american cities) are all called Union Station.
gpt
Basically a station is called a "Union Station" when tracks and other facilities were shared by more than one railway. It's always a passenger terminal.

This allowed passengers to quickly go from one service to an other, when railways were more regional. So, for example, you took one train to Chicago, and jumped on another train from there to Los Angeles.

In Europe they're called "Joint Stations".