the truck driver never existed, he was just an embodiment of David's fears

I felt sorry for the snake lady. I think that even people who can't stand spiders and snakes would have felt for her.

The Snakerama lady was a crucial witness, maybe the only witness, for Mann when he had to explain his story to the cops because everyone else thought he was either a nutter (the bus driver, Chuck's Cafe clientele) or just didn't want to get involved (the elderly couple on the highway when he wanted them to call the police).
I'm sure many other people on the roads would have come forward about being on the receiving end of that insane truck driver if the story went public. It could well have. It was a sensational story, and wreck, at the bottom of the cliff.

She lost a lot of her reptiles and arachnids, as well has the wholesale destruction of a lot of her business. Also her poor little coyote was scared to death. That lady was so obviously distraught that it was sad. But fortunately that maniac trucker got his comeuppance.

No, David Mann wasn't a very likeable person. Even so I was pulling for him all the way. I hate bullies.

I, too, felt bad the snake-a-rama got destroyed but never fear as the old lady was able to get a bi-plane up and running for "Silver Streak" in 1976.
"Hey Steve, you ever buzz sheep?"

Look out for the snakerama lady in Spielberg's 1979 comedy movie '1941' when John Belushi (Capt. Kelso) lands his aircraft at the very same gas station and demands "Fill her up!..Ethel" to which she replies "Where?"
A nice little nod to Duel!
He's going in to your room, it's
you
he wantsoffer him yourself!!

I thought the truck driver was a nice enough guy. He was just minding his own business and was tolerant of Mann, right until he threatened to go to the cops. Understandably he got pissed. If some mug knocked the sandwich out of my hand for no reason I would react like that too.

I felt sorry for the snake lady, too, as she not only had her business destroyed, but she was also given the burden of recollecting all of the snakes and spiders that survived.
As for the truck driver that Mann falsely accuses, I won't lie, I laughed when Mann slapped the sandwich out of the guy's hand! At that point, however, I just knew David was in for it!

The truck driver Mann falsely accused at least got a free beer out of the deal.