To film the striking images of a deserted New York City, the cast and crew had to start filming at dawn in order to capture the city before the early morning rush. This gave them no more than an hour or two per day in which to film the sequence.
On the bookshelf behind the bed in which Ben Thacker is recovering, is a copy of "The Proud Land" by James Lee Bartlow. This is the book supposedly written by Bartlow, played by Dick Powell in The Bad and the Beautiful (1952).
When Ralph marks his route to New York City on the map, he starts at a point in the center of Pennsylvania. There is no real town of Chatsburg in PA, but there is a town near his starting point called "Bellefonte" (the character Ralph Burton in the movie is played by Harry Belafonte).