All public highways in this state which have been a part of the route of a state highway and have been or may hereafter be no longer necessary as such, if situated outside of the limits of incorporated cities or towns, shall, upon certification thereof by the state department of transportation to the legislative authority of the county in which any portion of the highway is located, become a county road of the county, and if situated within the corporate limits of any city or town shall upon certification thereof by the state department of transportation to the mayor of the city or town in which any portion of the highway is located become a street of the city or town. Upon the certification the secretary of transportation shall execute a deed, which shall be duly acknowledged, conveying the abandoned highway or portion thereof to the county or city as the case may be.