The 1936 US highway system
Here you can see how detailed this map is.

This Continental Oil Company travel guide was assembled for a private party back in 1936. You can see the route in the first image above. The guide is scanned into two very high resolution PDF files at 405 and 435 megabytes. Wait for the downloads to complete. When viewing the file in your computer, tablet or phone, wait for the file to completely load then zoom in and enjoy.

The files can be found here. Your best bet to view the files is via a desktop or laptop computer and via the Adobe Acrobat application.