On Union Stations and Airports

Not sure why Americans are so into 'Union Station'. You see it in both railroads and airports. Why make multiple operators cluster together in a single location? The Union Station is a particularly American phenomena: A place where all the trains comes together. A 'union station' is nice if you are transferring between trains, or between different types of trains.It makes sense to connect the commuter rail network to the rapid transit network. But when a station is just a terminal for a particular transportation provider, why bother? Why spend all the money to aggregate it all together in a centralized location? Paris, London, Barcelona: They all have multiple passenger railroad terminals: each major provider built their own. It's worth noting, in America, that 'Union Stations' are always a civic project. And I feel I must suggest that such civic projects are a form of white elephant: a yearning for an intermodal 'Grand Central Terminal' that is neither intermodal, nor central? But only 'grand' and 'a terminal'.

Which brings to mid the question of airports: Why do we need to have a 'Grand Central Airport'? Airports with non automobile access are in the minority--only a handful have passenger rail. Providing road access (even a divided highway) to multiple airports is certainly feasible.

Why do we connect airlines to other airlines? Why shouldn't each airline have its own airport, in the way in which passenger railroads once had their own terminals. Endlessly expanding existing airports is costly: The older the airport, the more likely the land around it is urbanized, and the more difficult to expand the airport. Also the more likely that the existing airport property is already developed, and adding new airport facilities (terminals, hangers, shopping) requires demolishing existing structures, like trying to add a new couch in a small apartment.

Admittedly, it makes some sense to combine multiple airlines into a single airport: They can enjoy the agglomeration economy of sharing a bit of infrastructure no single airline could afford on its own: The runways. (And to a lesser extent consumer facilities like baggage handling and rental car stands).

But is that always worth it? The mayor of Houston (IIRC) recently said: "Great American Cities have multiple airports". There is a reason for that: There is no reason to centralize all the airlines into a single airport, especially if that airport is running up against capacity constraints.