§ 42. Maintenance of detours during construction. The maintenance and repair of any highway or right of way designated by official order of the department of transportation for use as a detour, during the construction, reconstruction, or improvement of a state highway, shall be under the supervision of the department of transportation and shall be paid out of the construction fund. Such highway or right of way designated as a detour by the department of transportation shall be deemed as an improved highway during construction, reconstruction or repair, when the detour is necessary, and shall be maintained, repaired and under the supervision of the department of transportation for the period of necessity only.