Trivia: Mentioned in the DVD commentary, is that the Tunnel (used to trap McClane and Farrel with traffic from both directions in DC) was an open tunnel and they had to shoot at night because they could not afford to cover it with their production budget. This is obvious from most of the shots pointed to the room where you can see a "break into night" opening.
Trivia: The only film in the franchise to not receive an R-rating in the US. 20th Century Fox pushed for the film to have a lighter PG-13 rating. Star Bruce Willis and director Len Wiseman chose to simply film the movie that they wanted to make without worrying about the rating during filming (as so not to negatively influence the film's production or feel they were holding back too much), leaving the necessary editing for the PG-13 rating for post-production editing. An unrated version of the film was released later on DVD and Blu-Ray that retains much of the violence and profanity that was cut for the PG-13 rating.