I was just wondering if these things really existed? Like if a semi truck wanted to do something illegal would a blocker car actually exist that would draw the police away from the trucks? In the movie these trucker caravans seem to be able to defy the laws at will and do whatever they want, Why does it seem like there was such an emphasis on truckers throughout movies and popular culture in the 70s in the US?
To address the latter half of your question, the New Hollywood movement emerged in the early 1970s, a reaction to the stiff nature of the current Hollywood establishment. Directors such as Francis Ford Coppola and Steven Spielberg were starting their own companies. This led to the production of more films with an anti-establishment attitudes because there was less regulation.
Why were trucks popular? A transcript, this Newspaper article, and this article by Amy Lively discuss various trucker strikes in the 1970s. There are plenty of primary sources regarding this topic. The 1970s were a time of high gas prices and a national speed limit to help ration gas. These restrictions severely limited the viability of the trucking industry. Truckers would routine block highways in huge convoys to protest the speed limit. In 1974, per the transcript, truckers went on strike and stopped trucking.
CBs were popular as they gave truckers the ability to communicate regarding gas stations that had gas and alert each other to speed traps. They became further popular as people saw them in movies and on TV.
The road has always been an example of freedom, freedom to travel and explore, freedom from the 9-5 treadmill. Jack Kerouac's The Road is a testament to this. In 1968, we had Woodstock and counterculture was in full swing. In 1969, we had Easy Rider, detailing two guys' motorcycle journey across the Southwest. In 1971, we had Vanishing Point, detailing a man's disregard for traffic laws and "the man" as his travels across the country.
Road movies were a popular genre to begin with, but as the fuel crisis heightened, the plight of truckers became more widely known. In 1974, there was a TV show called "Movin' On" that detailed the fictional daily lives of two independent truckers. In 1975, there Bill Fries released "Convoy" under the pseudonym C.W.McCall. During this period you had also Smokey and the Bandit (1977), Handle with Care (1977), Breaker! Breaker! (1977) High-Ballin' (1978), and Convoy (1978).
"Smokey and the Bandit" was originally intended to be a B-Movie cash cow taking advantage of the CB Craze, but instead it launched a genre of its own (Smokey)
Were blocker trucks actually used? I can find no accounts of them being used.
In "The Northern Forest" (Dobbs and Ober, 1995), the authors describe a mass protest by residents of the Adirondack State Park in New York where they drove up the highway blocking all lanes, but going at the exact speed limit. This naturally caused quite a backup. Is this the sort of thing you are talking about?