The best that I can see in my travels around the country;is that Subway is
the new "mom and pop" on the American family business scene.

In the Delta I ran into a Hindu couple from Bangladesh,  in Tenn  a Russian
lady and her son   and many young husbands and wives mostly  in their 30 's
running the show at lunch  from Arkansas to South  Carolina . So if your sons
dream is to own one of these ,he is not alone ,and  considering the culinary
aspects of the American public ,he will be able to  retire by the time he is 40.
But concerning the motif of the Subway interior
 there are several NYC photos that I do not recognize large stone  elliptical
structure ,( Bronx court house /queens? )and on the map there are  some
stations missing and so not yet built .I think the 42/ 5th ave stop isn't  there ,
and several others
Also the perspective of some of the photos would not be possible today..My
guess is they are pre war photos (1939) as the Botanical gardens in Brooklyn
look too new .and the Hoboken car ferry(shown ) is still running (took it  from
that suburban paradise Joisey many a time , Mom in swept wing sun glasses
,brother in Davy Crocket hat , sister wanting nothing to do with all of us  ) Py