Trunkline Maps
These one-sided maps show the road surface types (Cement Concrete, Bituminous Concrete and Sheet Asphalt, Waterbound Macadam, Gravel, Sand-Clay, etc) or Condition (Good, Under Construction, Poor but Passable, Impassable, etc). 
Know Issues are:
1919 July 1 (Lower Peninsula), July 1 (Upper Peninsula)
1920
1922 Sept 1, Sept 15(LP), Oct 1, Oct 15 (UP)
1923 May 15, June 1, June 15
1926 Nov 15
1928 Oct 1
1930 July 1
All are needed for my collection, except the Oct 15, 1922 Upper Peninsula map shown below.

A 1974 Trunkline map was also made, but its purpose is unclear.  See the scan of the lower right corner below.

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