§ 115-a. Abandonment of unused portions of town highways on county road system. Whenever a county road or part thereof constructed as part of the county road system deviates from the line of an existing town highway, or from the line of a former town highway within the limits of an incorporated village, as shown on the map of the county road system, the board of supervisors by resolution duly adopted upon the recommendation of the county superintendent of highways, and pursuant to a written agreement with the town board or village board of trustees, or in the event such an agreement cannot be reached with the approval of the commissioner of transportation, may abandon to the town or the incorporated village as the case may be for future maintenance, that part of the town highway or former town highway within the limits of an incorporated village not improved and modify the map of the county road system accordingly. The portion of any town highway or former town highway within the limits of an incorporated village excluded from the county road system shall be maintained by the town or village in which it is located.