How they did it...
I saw this movie as a kid way back in the 60s. I could never get over how they managed to show an empty New York City.
Later, as an adult, I worked in NYC, at the very location where the filmed the ending.
It's in the Financial District, just off of Wall Street, on Exchange Place. I worked in the building with the big arched opening that can be seen behind one of the actors - 20 Exchange Place.
They could easily have shot the whole scene on a Sunday morning, since that area is pretty much deserted on weekends because the stock market is closed.
20 Exchange Place was turned into condos in the late 90s, so there is much busier than it ever was in 1959.
"Don't call me 'honey', mac."
"Don't call me 'mac'... HONEY!"