Director Sam Peckinpah allowed actor and long-time associate James Coburn to work on the movie as a second-unit director to get his DGA card, and rumour has it that Coburn actually directed some scenes when Peckinpah was "unwell."
The Mack truck in the shootout scene on the Bridge was actually damaged so badly that it broke down just moments before filming the scene and had to be pushed across the bridge by a bulldozer to complete the scene.
The song had been written in 1974 by Bill Fries (aka CW McCall) for a series of bread commercials, and the result was a popular trend with CB radios and trucker lingo. By the time the movie went into production in 1977, the trend had already faded, but that didn't stop it from being a box office hit.
Sam Peckinpah's original cut of Convoy was around three and a half hours long. Since he wasn't involved in post production, movie was edited by studio staff and editor Garth Craven down to 1 hour and 50 minutes long running time.
Although the movie was inspired by the 1976 song of the same title, the song really didn't have much of a plot. So after the screenplay was written, Bill Fries (aka CW McCall) recorded a new version of the song, with lyrics that incorporated the characters and events of the film. This is the version that is played during the final credits.
The "tank" used at the end of the movie is actually an M42 40mm Self-Propelled Anti-Aircraft Gun called a "Duster". It was used in the Korean War for anti-aircraft and in the Vietnam War for truck convoy protection duty.