The dialogue in the limo in which Tom asks the driver to raise the sliding partition was improvised and initiated by Kevin Costner. As the other actors' reactions seemed more natural than the scripted version, it was kept in the final print.
Kevin Costner did actually roll over the hood of a moving car during one of the chase sequences. According to the film's original press material, an insurance executive approached director Roger Donaldson after that stunt and said: "Don't you ever... ever... EVER... do that again!"
Kevin Costner performed most of his own stunts. He even drove without wearing his prescription glasses, much to the dismay of the film's insurance company.
Sean Young said in an interview that while she was fine being naked in certain scenes, Kevin Costner, who was dressed, was very nervous about her being nude.
Some, though not all, scenes supposedly inside the Pentagon were filmed there. The most notable on location scene occurred inside the actual office of the Secretary of Defense.