The following factors and weights shall be used in determining the amount to be allocated to each of the counties for road purposes in the year 1972 and each year thereafter: (1) Rural population of each county, as determined by the most recent federal census, twenty percent;
(2) Total population of each county, as determined by the most recent federal census, ten percent;
(3) Lineal feet of bridges twenty feet or more in length and all overpasses in each county, as determined by the most recent inventory available within the Department of Roads, ten percent, and for purposes of this subdivision a bridge or overpass located partly in one county and partly in another shall be considered as being located one-half in each county;
(4) Total motor vehicle registrations, other than prorated commercial vehicles, in the rural areas of each county, as determined from the most recent information available from the Department of Motor Vehicles, twenty percent;
(5) Total motor vehicle registrations, other than prorated commercial vehicles, in each county as determined from the most recent information available from the Department of Motor Vehicles, ten percent;
(6) Total miles of county and township roads within each county, as determined by the most recent inventory available within the Department of Roads, twenty percent; and
(7) Value of farm products sold from each county, as determined from the most recent federal Census of Agriculture, ten percent.
