Michel, have you read this interview:
Shore says that he deliberately included cars in his photos just because they provide a time stamp that most westerners cannot ignore. He cites Walker Evans as an inspiration.
I try for the most part to photograph what is there in front of me, and find that if I do start to stage manage a scene it usually gets more boring. Nature and Fate have better imaginations than I do. If the cars are there, they come along for the ride. Friedlander's quote goes to the heart of it:
"I only wanted Uncle Vern standing by his new car (a Hudson) on a clear day. I got him and the car. I also got a bit of Aunt Mary's laundry, and Beau Jack, the dog, peeing on a fence, and a row of potted tuberous begonias on the porch and 78 trees and a million pebbles in the driveway and more. It's a generous medium, photography."