(a) The total of expenditures from the State Public Transportation Fund under paragraphs (4), (5), and (6) of Code Section 32-5-21 plus expenditures of federal funds appropriated to the department, not including any state or federal funds specifically designated for maintenance and operations, any project undertaken for purposes of the Developmental Highway System provided by Code Section 32-4-22, or any project of the Georgia Regional Transportation Authority, Georgia Ports Authority, or Metropolitan Atlanta Rapid Transit Authority, shall be budgeted by the department over each five-year period commencing July 1, 1999, and quinquennially thereafter such that at the end of such period funding obligations equivalent to at least 85 percent of such total for such period shall have been divided equally among the congressional districts in this state for public road and other public transportation purposes in such districts; with the remainder of such total divided among congressional districts such that five percent of such total for such period shall have been obligated for public road projects incidental to economic development purposes anywhere in this state, and no congressional district shall have received funding obligations pursuant to this subsection for such period which are more than 20 percent greater than that received by any other congressional district pursuant to this subsection for such period.

(b) The board may upon approval by two-thirds of its membership authorize a reduction in the share of funds allocated pursuant to this Code section to any congressional district if such supermajority of the board determines that such district does not have sufficient projects available for expenditure of funds within that district to avoid lapsing of appropriated funds.

(c) Provisions of this Code section may be waived pursuant to subsection (b) of Code Section 32-5-1 only upon approval by two-thirds of the membership of the board.