This is similar to a project I worked on where the audience was "the entire state". We had the same question. The solution for us was to define three key use cases. Therefore, if your train station has three key use cases you might be able to find your way to what you're after. Until we had our use cases, devs were just doing fluffy work around the edges and nothing meaningful, because we had no measure.
So, perhaps rather than a persona straight up, you define a use case. And from there think about people. Otherwise you end up bashing your head against a wall of all possibility.
Hope this helps!