Rand McNally begins 28-year run as publisher of the state highway map. Introduction of an alphabetical index to settlements along with a key to their location on the map and their respective populations. First map to include state police posts. 1937 First truckers map issued showing weight restrictions on roads and, later, bridge load limits and overhead clearances. 1939 First map to show scheduled airline routes.
Department begins placing state highway maps on display at roadside picnic sites.
1940 Plans for building standard Highway Department picnic table printed on maps by popular demand. 1940 First photograph appears on cover. All previous covers were artwork drawn by department staff. 1942 U.S. Army asks Highway Department to discontinue issuing maps for security reasons. Department issues special road map minus potentially sensitive information such as airports and new road construction in the vicinity of war plants.