(1) The department shall adopt a sufficiency rating system for roads on the State Highway System.
(2) Such system shall include, but shall not be limited to, the consideration of the following factors:
(a) Structural adequacy;
(b) Safety; and
(3) The determination of rating, at a minimum, shall take into consideration the volume of traffic using the roads and the minimum engineering standards required to safely accommodate such volume of traffic; the age of the roads; the width of pavement and shoulders; the number and degree of curves, both horizontal and vertical; ridability; and maintenance economy.