Funds apportioned to this state pursuant to subdivision (b)(2) of Section 104 of Title 23 of the United States Code for the Federal-Aid Secondary System shall be apportioned by the department. At least 98 percent of such funds shall be apportioned among the counties in the manner and in accordance with the formula set forth in that subdivision, except that the census figures used in making the apportionment shall be those contained in the latest available federal census.