Michigan Compiled Laws, Chapter 247. Highways § 247.448

Sec. 48.  The apportionment of benefits for the proposed improvements against the county at large, or against any city at large, and against the several townships at large, as made by the county road commissioners, or the state highway commissioner, or in case of appeal by the county or any township as made by the board of review hereinbefore provided for shall be final and conclusive and shall not be changed by the board of review herein appointed to review the apportionment of benefits upon lands.  The board of review herein shall proceed at the time and place specified in their notice to hear the proofs and allegations of the parties in interest, and shall proceed to view the lands benefited by the proposed improvement, and to review all of the apportionments for benefits made by the county road commissioners or the state highway commissioner, on lands benefited in the assessment district on account of such improvement, and if in their judgment there be manifest error in any such apportionment upon lands benefited, they shall make such changes therein and equalize the same as they deem just and equitable.  All boundaries of the special assessment district as made by the county road commissioners, or the state highway commissioner, or by the board of review hereinbefore mentioned, upon appeal shall be final and conclusive;  the board of review appointed to review the apportionment of the per cent upon lands shall have no power to add additional lands to the special assessment district.  But 1 appeal shall be acted upon to review the apportionment of the per cent of benefits assessed upon lands in the assessment district.