I collect and deal in road maps. Such maps definitely exist, but perhaps not published in the ways you may think of nowadays. The Northeast in particular was better mapped than most of the rest of the US was, as all the cities were fully industrialized and people were not only moving out to the suburbs but buying cars and going on Sunday drives.

Most cities would have produced their own maps, for the purposes of town planning. States started producing their own road maps in the 1910s, with most states putting out a new map every year by the early 1930s. These are the maps nowadays you can pick up at rest areas and are referred to as "official maps", as in "an official 1952 Massachusetts map".

Atlases of the US existed, but for detailed route information there were various competing companies that made touring guides, mainly the Automobile Green Book, Automobile Blue Book and Mixer's Motor Tours. These guides were largish bound books that had have turn-by-turn directions through large cities, as signing wasn't uniform and the status of many roads changed rapidly from year to year. AAA and other auto clubs produced strip maps that were similar in design but distributed and used one page at a time.

The Depression did these companies in, as well as one other prominent cartographer (the Clason Map Company), although the makers of the Green Book held on for longer than the others.

From the 1920s to the 1980s or so there were three prominent cartographers for road maps: Rand McNally, who everyone's heard of; HM Gousha, which is pronounced to rhyme with "touche" and mostly contracted its services out to oil companies; and General Drafting, which was a subsidiary of Standard Oil of New Jersey (Esso or Exxon) and mostly gave its maps away at its own service stations but did do a small amount of contracting.

All these maps and guides can be found on eBay, although the Blue Books can be hard to search for because the name is similar to the KBB people use for car prices. Most are reasonably priced but maps before the 30s can be quite valuable depending on the maker, area covered, cover design or oil company if it's a gas station map.

I suspect digitalization efforts have been minor because there just plain hasn't been a demand for the material online. Some libraries have quite extensive collection of maps of their local area, and some state DOTs, such as North Carolina's, have digitized and posted their old official maps.