Of the 32 professional racing drivers who participated or were seen in the film, five died in racing accidents within two years and another five in the following ten years.
John Frankenheimer refused to film cars moving slowly, then speed the film up. He felt the average moviegoer would be able to notice the difference.
James Garner did all his own driving. During breaks in filming there were several mini races in which Garner either tied or bettered the professional drivers hired for filming.
Crowds can be difficult to manage simply because of the effort needed to maintain their concentration. During the filming of Grand Prix (1966) there was a scene where a flaming car is driven into the pits. It was about 4 o'clock in the afternoon and the director, John Frankenheimer, was disgusted by the crowd's lack of reaction to the dramatic action during the rehearsals. They appeared to be more interested in their tea break. Frankenheimer called his special effects man over and told him to 'blow up the tea van' when given the signal. The unit went for a take. The flaming sports car came into the pits. The crowd looked on. The signal was given and the tea truck exploded. The crowd reacted and Frankenheimer got his shot' This is an extreme example of how to direct crowds. (from "Production Management for Film and Video" by Richard Gates)
The opening sequence with all the closeups of the car parts and the multi-image montages was shot and edited by Saul Bass.