When everyone gets out of their cars in the traffic jam and watches the comet pass overhead, they were really looking at a crew helicopter passing over. In post production, the helicopter was covered up with the comet.

The traffic jam that Leo Beiderman travels through at the end was made up of 2,000 cars and 2,500 people on a not-yet-opened stretch of highway in northern Virginia.

If you happen to have the DVD version of the film, have a look at one of the trailers. In the movie trailer they show the comet hitting the ocean at an almost right-angle. In the actual movie the comet enters the atmosphere at an angle, thus letting the people watch the comet travel to across the sky into the ocean.

A sorta nice inside joke: At one point when the President is speaking we see a crowd watching the broadcast in New York City's Times Square. A long shot from above shows the crowd in the streets, and a nearby cinema's marquee shows that the cinema is playing "Fire In the Sky". "A Fire In the Sky" is the title of a movie from 1978 about a comet that hits Phoenix. But this is where it gets sorta tricky: I looked the title up, and noticed something: the title of the movie, notice, is "A Fire In the Sky", while the marquee read simply "Fire In the Sky". That is the name of a movie about the supposedly true story of a guy that was abducted by aliens. A inside joke that doesn't work, due to bad research (or lettering).

In a recent American TV airing of the film (January 2004), any scene depicting the former World Trade Center towers were removed, due to existing September 11 sensibilities.