The Odd Chpters

In chapters such as 7, 9, and 12 Steinbeck uses third person to tell about events such as the car dealership, HWY 66, and the farmers selling their possessions. These chapters are obviously relevant to the story of the Joads summing up past chapters and foreshadowing upcoming chapters. But are the people that he discussed in these chapters the Joads, even though he does not say their name, or are they nameless to represent that a lot of people during the era were in the same situation that the Joads were in? And do these chapters seem a little repetitive since they are just a review of what he talked about in past chapters and just tell the reader what is going to happen to the Joads in the upcoming chapters? Is he using these chapters to make the book longer or is he trying to accomplish something with these odd chapters?