Here's a fascinating find on the web: the 1937 handbook entitled "The Right to Drive", published by the Plymouth Motor div. of Chrysler and prepared in cooperation with the Detroit Police Dept. This was an era of explosive car growth but no standardized system for road/traffic markings, drivers licenses, etc. and little knowledge of driving and safety culture. Lots of great old pics of Detroit along with some interesting/humorous explanations.

http://http://www.us-highways.com/trtdr00.htm