Shipping freight by truck long-distance has come a very long way since those foundational post WWII decades when the U.S. became manufacturer not only to the world but to millions of American boomers yearning to be free, wanting to consume more of everything in ever farther-flung suburbs.

Hauling U.S. industry’s growing post-war manufacturing and agriculture output meant a growing industry that today moves more than 70% of all the freight, some 10.5 billion tons of freight annually via 3.4 million heavy-duty Class 8 trucks. According to ATA, it takes 3.5 million truck drivers to move it all, and thanks in large part to them, are responsible for generating $726.4 billion in gross freight revenues (primary shipments only) a figure representing 81.5% of the nation’s freight bill in 2015.

http://www.trucking.org/News_and_Information_Reports_Industry_Data.aspx

The Owner-Operator Independent Drivers Association’s OOIDA Foundation does focused research on owner-operators. The group says among those 3.5 million drivers, approximately 350,000 are owner-operators -- however, this group is not as independent as one might suspect; recent statistics say most of these folks (+ 75% or higher) lease to larger carriers and operate under that carriers DOT number.