"Duel" is a thriller about a traveling salesman called David Mann, who is played by Dennis Weaver. Mann is driving home on the back roads of the California desert. For no apparent reason, he is terrorized by a large truck, which repeatedly chases and attempts to run him off the road. The film consists of a cat and mouse struggle between the truck and Weaver's character. Throughout the film, the driver of the truck remains anonymous and unseen, with the exception of two separate shots where his arm beckons Weaver to pass him, and another shot where Weaver observes the driver's snakeskin boots. His motives for targeting Weaver's character are never revealed.
In reality, the truck driver was played by the late stuntman and character actor Carey Loftin (though others, including Spielberg himself, drove the truck at times).
Despite its simple plot, a low budget (only $375,000) and very short filming deadlines (originally 10 days), the movie maintains a high level of suspense due to Spielberg's taut direction and the script's refusal to resolve the central mystery of the driver. The film's success put the young Spielberg on the map in Hollywood, and enabled him to move beyond directing for television.
The truck, a Peterbilt 351,   was chosen for its "face". For each shot, several people had the task to make it uglier, adding some "truck make-up". And you can see several car license plates hung on the front of the truck, signifying that it's not his first chase. The car was also carefully chosen, a red Plymouth Valiant with an unreliable and underpowered engine to signify the weakness of the David Mann character.
The script is adapted by Richard Matheson from his own short story. It may have been inspired by a 1947 episode of the old-time radio series "Lights Out" entitled "What the Devil", which had a similar plot but different resolution.
This TV spot for a syndicated airing of the movie was originally posted to YouTube by KLXT77.