According to the book "Sophia Loren: A Biography," Ava Gardner gave Loren the following advice during production: "Always shoot your close-ups first thing in the morning, honey, 'cause your looks ain't gonna hold out all day."
This movie's storyline features the potential outbreak of a deadly pneumonic plague virus on a train from a germ infected passenger. As a child, Writer and Director George P. Cosmatos experienced a cholera outbreak while living in Egypt. Cosmatos once said: "To me, an epidemic seems more destructive than an earthquake, a fire, or even a bomb, and a man-made epidemic, such as is shown in this movie, is the most despicable of all. We are our own worst enemies, because we're killing ourselves with so-called progress."
The title refers to a bridge in the movie called the "Kasundruv Bridge." The architectural structure used to play this, was the Viaduct of Garabit, which is located in the South of France. It was built between 1881 and 1884, and was manufactured by Gustave Alexandre Eiffel of The Eiffel Tower fame. It stands 122 meters tall, by 565 meters long. The Garabit Viaduct is still used today as a railway bridge.
Production on the movie in Switzerland was delayed, due to vandalism. The train was graffitied with political slogans on one roof, and inside the carriages, whilst sitting stationery overnight at Delemont Station. The train roof graffiti was only discovered when aerial photography was being conducted from a helicopter.
The Swiss Railway line organization Schweizerische Bundesbahnen-Berne supplied a full train to the production. This included the engine, a dining car, a sleeper, numerous train cars, and carriages.