The governing body of a governmental unit may issue bonds of the governmental unit for the purpose of constructing or improving highways of the governmental unit. The governing body of the governmental unit, and in the case of townships and road districts only with written approval of their respective county engineers or superintendents of highways, and in the case of consolidated road districts only with written approval of their county boards, shall, before issuing such bonds, by resolution determine that it is necessary to issue bonds of the governmental unit for the purpose of constructing or improving particular highways, and specify the type of construction or improvements, the proposed width of the highways, together with an estimate of the cost of such construction or improvements and the amount of bonds to be issued.