The bridges on the public roads of this state shall be divided into three (3) classes:
(1) Bridges over sixty feet (60') in length, exclusive of abutments, shall be bridges of the first class;
(2) Bridges of not less than thirty feet (30') nor more than sixty feet (60') in length, exclusive of abutments, shall comprise the second class; and
(3) All bridges less than thirty feet (30') in length shall comprise the third class.