[piva00]

Stockholm with a bit over 1 million people has an express train from Arlanda airport to the center of the city, it goes at ~200km/h making the transit of ~40km in 20-25 minutes.

I don't understand why it would be inefficient for one of the busiest airports in the world to one of the largest cities in the world to have a similar setup.

[jonnybgood]

Do you know where JFK is? JFK does not sit outside the city like Arlanda. JFK is in the NYC Queens borough surrounded by highly dense urban sprawl. That setup makes sense for an airport that sits far outside the city.

No track to JFK can support anything near a 200km/hr train and building a track for such a train is a nonstarter.

[rsynnott]

It'd likely have to go largely underground. This is the approach being taken for Dublin Airport (again, a far, far smaller city than NYC); it'll be served by a largely underground metro line, running every 3 minutes each direction, taking about 20 minutes from the city centre.

Now, the catch there is that this metro isn't going to the airport, it's going _through_ the airport. Even without the airport it would be justifiable, so the airport kind of gets it for free. That's probably the only scenario where you can justify this sort of thing; it would be comically overkill if it was just to serve the airport (it will be able to move 20,000 people per hour per direction, which is... a lot more than the airport can move.)

That said, you'd think something along these lines might be justifiable; as you say, the area surrounding JFK is dense.