[4][5] On the east side of Munger, the roadway crosses a branch line of the Huron and Eastern Railway.

[5][6] The highway turns north on Main and crosses the rail line a second time as they both exit town.

[4][5] The highway passes through the village of Akron on Beach Street, crossing the rail line a final time.

[7] No section of M-138 has not been listed on the National Highway System,[8] a network of roads important to the country's economy, defense, and mobility.

[12][13] When M-24 was extended northward from Caro in 1997, it supplanted the M-138 designation from the Akron area north to Unionville; the latter highway was truncated to its current form as a result.