Back in the early 80s I was a long haul trucker - 24 hrs a day, 362 days a year. You have to understand that it's a subterranean world that you can't experience unless you're there. It's your life.
So I pull into the 76 in Ontario, CA one night (they used to run the hookers in with large RVs and we all had fun insulting the customers on the radio) and it's obvious something funny is going on. I note it, but follow my usual pattern and go get some grub.
On the way out, after wandering through the store (it's a rule - you have to wander through the store) there's all these lights and people and general weirdness going on. I note it, and keep going. Some guy grabs me and says I can't go out there, that they're filming.
I wasn't rude or arrogant or uppity or anything, but he grabbed me, and me the truck driver, and me the driver who was on the job, and me the driver who was on the job at a truck stop. And he's, you know, a movie guy. So I just sort of nodded and kept going. That's when Terri Garr and Howard Hessman came rolling in driving a RV. They were obviously having this huge argument, and I felt bad, because I liked them both quite a lot then, and it upset me that they weren't getting along. Then I realized, oh, it's a movie - they're acting. Cool. So I stopped to watch.
Except everything ground to a halt and all these people were yelling and talking on their radios. Then the guy comes up again and tells me I'm in the scene. Ah.
The weird thing was, the fake drivers they had to walk in the background didn't look anything like drivers. They sort of looked like movie versions of lumberjacks - all plaid coats and big beards. I remember being kind of insulted by that. It was fun to watch though - they wouldn't let Howard drive the RV back out for next takes, he could only drive it in. And they hosed down the pavement before each take (they still do this - check the pavement in most car scenes or ads.)