Notes
From www.digitalhistory.uh.edu:
"During the 1920s, the country doubled its system of roads and highways. The nation spent over $2 billion annually building and maintaining roads. By 1929, there were 852,000 miles of roads in the United States, compared to just 369,000 miles in 1920."
However, as will be seen, many of those roads were dirt, or worse, and ferries were the only means of crossing many rivers.