[delecti]

I don't know about you, but on a plane I'm definitely closer to other passengers for longer periods of time than I am on most metro rides. It also exposes you to people from a geographically wider spread, and many of those people have likewise been exposed to people from even more different places earlier in their trip.

[robjan]

That really depends. Many many people live in world cities where public transport is cramped and people from all over the world come and go in a constant stream.

[dredmorbius]

And how do those people from all over the world get there?

[robjan]

There are many ways. Boat; train; bus and, yes, flying. International commerce will not stop forever and as long as that's true people will travel.

[dredmorbius]

And border crossings by mode are?