Should any provision or section of this act be held to be invalid for any reason, such holding shall not be construed as affecting the validity of any remaining portion of such section or of this act, it being the legislative intent that this act shall stand, notwithstanding the invalidity of any such provisions or section. Nothing in this act contained shall be construed as permitting any board of county road commissioners to pledge future revenues derived from state collected taxes returned to such county for county road purposes which are by law required to be allocated to (1) any city or village, (2) the relief of assessment districts established under provisions of Act No. 59 of the Public Acts of 1915, as amended, or (3) the reduction of taxes for the payment of bonds.